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		Chemistry



		Chemistry is the area of science concerned with the study of the structure and composition of the different kinds of matter, the changes which matter may undergo, and the phenomena which occur in the course of these changes. Ancient civilizations were familiar with certain chemical processes—for example, extracting metals from their ores, and making alloys. The alchemists endeavored to turn base (nonprecious) metals into gold, and chemistry evolved toward the end of the 17th century from the techniques and insights developed during alchemical experiments.



		Robert Boyle defined elements as the simplest substances into which matter could be resolved. The alchemical doctrine of the four elements (earth, air, fire, and water) gradually lost its hold, and the theory that all combustible bodies contain a substance called phlogiston (a weightless "fire element" generated during combustion) was discredited in the 18th century by the experimental work of Joseph Black, Antoine Lavoisier, and Joseph Priestley (who discovered the presence of oxygen in air).



		Henry Cavendish discovered the composition of water, and John Dalton put forward the atomic theory, which ascribed a precise relative weight to the "simple atom" characteristic of each element. Much research then took place leading to the development of biochemistry, chemotherapy, and plastics.



		Chemistry is commonly divided into three main branches. Organic chemistry is the branch of chemistry that deals with carbon compounds. Inorganic chemistry deals with the description, properties, reactions, and preparation of all the elements and their compounds, with the exception of carbon compounds. Physical chemistry is concerned with the quantitative explanation of chemical phenomena and reactions, and the measurement of data required for such explanations. This branch studies in particular the movement of molecules and the effects of temperature and pressure, often with regard to gases and liquids.



		Molecules, Atoms, and Elements



		All matter can exist in three states: gas, liquid, or solid. It is composed of minute particles termed molecules, which are constantly moving, and may be further divided into atoms.



		Molecules that contain atoms of one kind only are known as elements; those that contain atoms of different kinds are called compounds. Chemical compounds are produced by a chemical action that alters the arrangement of the atoms in the reacting molecules. Heat, light, vibration, catalytic action, radiation, or pressure, as well as moisture (for ionization), may

Molecule of the Month
http://www.bris.ac.uk/Depts/Chemistry/MOTM/motm.htm

Pages on interesting—and sometimes hypothetical—molecules, contributed by university chemistry departments throughout the world.



		be necessary to produce a chemical change. Examination and possible breakdown of compounds to determine their components is analysis, and the building up of compounds from their components is synthesis. When substances are brought together

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		without changing their molecular structures they are said to be mixtures.



		*the atom*



		The atom is the smallest unit of matter that can take part in a chemical reaction, and which cannot be broken down chemically into anything simpler. The atoms of the various elements differ in atomic number, atomic weight, and chemical behavior.



		Atoms are much too small to be seen by even the most powerful optical microscope (the largest, cesium, has a diameter of 0.0000005 mm/0.00000002 in), and they are in constant motion. However, modern electron microscopes, such as the scanning tunneling microscope (STM) and the atomic force microscope (AFM), can produce images of individual atoms and molecules.



		*atomic structure* The core of the atom is the nucleus, a dense body only one ten-thousandth the diameter of the atom itself. The simplest nucleus, that of hydrogen, comprises a single stable positively charged particle, the proton. Nuclei of other elements contain more protons and additional particles, called neutrons, of about the same mass as the proton but with no electrical charge. Each element has its own characteristic nucleus with a unique number of protons, the atomic number. The number of neutrons may vary. Where atoms of a single element have different numbers of neutrons, they are called isotopes. Although some isotopes tend to be unstable and exhibit radioactivity, they all have identical chemical properties.



		The nucleus is surrounded by a number of moving electrons, each of which has a negative charge equal to the positive charge on a proton, but which weighs only 1/1,839 times as much. In a neutral atom, the nucleus is surrounded by the same number of electrons as it contains protons. According to quantum theory, the position of an electron is uncertain; it may be found at any point. However, it is more likely to be found in some places than others. The region of space in which an electron is most likely to be found is called an orbital or shell. The chemical properties of an element are determined by the ease with which its atoms can gain or lose electrons from its outer orbitals. These shells can be regarded as a series of concentric spheres, each of which can contain a certain maximum number of electrons; the inert gases have an arrangement in which every shell contains this number. The energy levels are usually numbered beginning with the shell nearest to the nucleus. The outermost shell is known as the valence shell as it contains the valence (bonding) electrons.



		atom, electronic structure The arrangement of electrons in a sodium atom and a sulfur atom. The number of electrons in a neutral atom gives that atom its atomic number: sodium has an atomic number of 11 and sulfur has an atomic number of 16.



		The lowest energy level, or innermost shell, can contain no more than two electrons. Outer shells are considered to be stable when they contain eight electrons but additional electrons can sometimes be accommodated provided that the outermost shell has a stable configuration. Electrons in unfilled shells are available to take part in chemical bonding, giving rise to the concept of valence. In ions, the electron shells contain more or fewer electrons than are required for a neutral atom, generating negative or positive charges.

Look Inside the Atom
http://www.aip.org/history/electron/jjhome.htm

Part of the American Institute of Physics site, this page examines J. J. Thomson's 1897 experiments that led to the discovery of a fundamental building block of matter, the electron. The site includes images and quotes and a section on the legacy of his discovery.



		*atomic mass unit* This is the unit of mass that is used to measure the relative mass of atoms and molecules. Sometimes called the dalton unit, it is equal to one-twelfth of the mass of a carbon-12 atom, which is equivalent to the mass of a proton or 1.66 × 10^–27 kg. The atomic weight of an atom has no units; thus oxygen-16 has an atomic weight of 16 daltons but a relative atomic mass of 16.



		*atomic number* This is the number (symbol Z) of protons in the nucleus of an atom (sometimes called the proton number). It is equal to the positive charge on the nucleus.



		In a neutral atom, it is also equal to the number of electrons surrounding the nucleus. The chemical elements are arranged in the periodic table of the elements according to their atomic number.

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Discovery of the Elements

(– = not applicable.)

arsenic (As)
bismuth (Bi)
carbon (C)
copper (Cu)
gold (Au)
iron (Fe)
lead (Pb)
mercury (Hg)
silver (Ag)
sulfur (S)
tin (Sn)
zinc (Zn)

Joseph Black (oxide isolated by Humphry Davy in 1808; pure form isolated by Antoine-Alexandre-Brutus Bussy in 1828)

Karl Scheele (isolated by Henri Moissan in 1886)

chlorine (Cl)
manganese (Mn)
oxygen (O)

Karl Scheele
Johann Gottlieb Gahn
Joseph Priestley and Karl Scheele, independently of each other

1781

molybdenum (Mo)

named by Karl Scheele (isolated by Peter Jacob Hjelm in 1782)

isolated by Juan José Elhuyar and Fausto Elhuyar

1789

uranium (U)

zirconium (Zr)

Martin Klaproth (isolated by Eugéne Péligot in 1841)
Martin Klaproth

Louis-Nicolas Vauquelin

1798

beryllium (Be)

Louis-Nicolas Vauquelin (isolated by Friedrich Wöhler and Antoine-Alexandre-Brutus Bussy in 1828)

1801

vanadium (V)

niobium (Nb)

Andrés del Rio (disputed), or Nils Sefström in 1830
Charles Hatchett

cerium (Ce)

iridium (Ir)
osmium (Os)
palladium (Pd)
rhodium(Rh)

Jöns Berzelius and Wilhelm Hisinger, and independently by Martin Klaproth
Smithson Tennant
Smithson Tennant
William Wollaston
William Wollaston

1807

potassium (K)
sodium (Na)

Humphry Davy
Humphry Davy

1808

barium (Ba)
boron (B)

calcium (Ca)
strontium (Sr)

Humphry Davy
Humphry Davy, and independently by Joseph Gay-Lussac and Louis-Jacques Thénard
Humphry Davy
Humphry Davy

cadmium (Cd)
lithium (Li)
selenium (Se)

Friedrich Strohmeyer
Johan Arfwedson
Jöns Berzelius

Hans Oersted (also attributed to Friedrich Wöhler in 1827)

1826

bromine (Br)

Antoine-Jérôme Balard

1827

ruthenium (Ru)

G. W. Osann (isolated by Karl Klaus in 1844)

erbium (Er)
terbium (Tb)

Carl Mosander
Carl Mosander

1860

cesium (Cs)

Robert Bunsen and Gustav
Kirchhoff

1861

rubidium (Rb)
thallium (Tl)

Robert Bunsen and Gustav Kirchhoff
William Crookes (isolated by William Crookes and Claude August Lamy, independently of each other in 1862)

1863

indium (In)

Ferdinand Reich and Hieronymus Richter

Paul Lecoq de Boisbaudran

Jean Charles de Marignac

1879

holmium (Ho)
samarium (Sm)
thulium (Tm)

Per Cleve
Paul Lecoq de Boisbaudran
Per Cleve

1885

neodymium (Nd)
praseodymium (Pr)

Carl von Welsbach
Carl von Welsbach

1886

dysprosium (Dy)
gadolinium (Gd)
germanium (Ge)

Paul Lecoq de Boisbaudran
Paul Lecoq de Boisbaudran
Clemens Winkler

1894

argon (Ar)

John Rayleigh and William Ramsay



		(table continued on next page)

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		(table continued from previous page)

Date	Element (symbol)	Discoverer
1898	krypton (Kr) neon (Ne) polonium (Po) radium (Ra) xenon (Xe)	William Ramsay and Morris Travers William Ramsay and Morris Travers Marie and Pierre Curie Marie Curie William Ramsay and Morris Travers
1899	actinium (Ac)	André Debierne
1900	radon (Rn)	Friedrich Dorn
1901	europium (Eu)	Eugène Demarçay
1907	lutetium (Lu)	Georges Urbain and Carl von Welsbach, independently of each other
1913	protactinium (Pa) hafnium (Hf)	Kasimir Fajans and O. Göhring Dirk Coster and Georg von Hevesy
1925	rhenium (Re)	Walter Noddack, Ida Tacke, and Otto Berg
1937	technetium (Tc)	Carlo Perrier and Emilio Segrè
1939	francium (Fr)	Marguérite Perey
1940	astatine (At) neptunium (Np) plutonium (Pu)	Dale R. Corson, K. R. MacKenzie, and Emilio Segrè Edwin McMillan and Philip Abelson Glenn Seaborg, Edwin McMillan, Joseph Kennedy, and Arthur Wahl
1944	americium (Am) curium (Cm)	Glenn Seaborg, Ralph James, Leon Morgan, and Albert Ghiorso Glenn Seaborg, Ralph James, and Albert Ghiorso
1945	promethium (Pm)	J. A. Marinsky, Lawrence Glendenin, and Charles Coryell
1949	berkelium (Bk)	Glenn Seaborg, Stanley Thompson, and Albert Ghiorso
1950	californium (Cf)	Glenn Seaborg, Stanley Thompson, Kenneth Street Jr., and Albert Ghiorso
1952	einsteinium (Es)	Albert Ghiorso and co-workers
1955	fermium (Fm) mendelevium (Md)	Albert Ghiorso and co-workers Albert Ghiorso, Bernard G. Harvey, Gregory Choppin, Stanley Thompson, and Glenn Seaborg
1958	nobelium (No)	Albert Ghiorso, Torbjørn Sikkeland, J. R. Walton, and Glenn Seaborg
1961	lawrencium (Lr)	Albert Ghiorso, Torbjørn Sikkeland, Almon Larsh, and Robert Latimer
1964	dubnium (Db)	claimed by Soviet scientist Georgü Flerov and co-workers (disputed by U.S. workers)
1967	unnilpentium (Unp)	claimed by Georgü Flerov and co-workers (disputed by U.S. workers)
1969	rutherfordium (Rf)	claimed by U.S. scientist Albert Ghiorso and co-workers (disputed by Soviet workers)
1970	dubnium (Db)	claimed by Albert Ghiorso and co-workers (disputed by Soviet workers)
1974	seaborgium (Sg)	claimed by Georgü Flerov and co-workers, and independently by Albert Ghiorso and co-workers
1976	bohrium (Bh)	Georgü Flerov and Yuri Oganessian (confirmed by German scientist Peter Armbruster and co-workers)
1982	meitnerium (Mt)	Peter Armbruster and co-workers
1984	hassium (Hs)	Peter Armbruster and co-workers
1994	ununnilium (Uun) unununium (Uuu)	team at GSI heavy-ion cyclotron, Darmstadt, Germany team at GSI heavy-ion cyclotron, Darmstadt, Germany



		*chemical bonds*



		The principal types of bonding are ionic, covalent, metallic, and intermolecular (such as hydrogen bonding).



		The type of bond formed depends on the elements concerned and their electronic structure. In an ionic or electrovalent bond, common in inorganic compounds, the combining atoms gain or lose electrons to become ions; for example, sodium (Na) loses an electron to form a sodium ion (Na⁺) while chlorine (Cl) gains an electron to form a chloride ion (Cl^–) in the ionic bond of sodium chloride (NaCI).



		In a covalent bond the atomic orbitals of two atoms overlap to form a molecular orbital containing two electrons, which are thus effectively shared between the two atoms. Covalent bonds are common in organic compounds, such as the four carbon-hydrogen bonds in methane (CH₄). In a dative covalent or coordinate bond, one of the combining atoms supplies both of the valence electrons in the bond.



		A metallic bond joins metals in a crystal lattice; the atoms occupy lattice positions as positive ions, and

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		ionic bond The formation of an ionic bond between a sodium atom and a chlorine atom to form a molecule of sodium chloride. The sodium atom transfers an electron from its outer electron shell (becoming the positive ion Na⁺) to the chlorine atom (which becomes the negative chloride ion Cl^–). The opposite charges mean that the ions are strongly attracted to each other. The formation of the bond means that each atom becomes more stable, having a full quota of electrons in its outer shell.



		covalent bond The formation of a covalent bond between two hydrogen atoms to form a hydrogen molecule (H₂), and between two hydrogen atoms and an oxygen atom to form a molecule of water (H₂O). The sharing means that each atom has a more stable arrangement of electrons (its outer electron shells are full).



		valence electrons are shared between all the ions in an ''electron gas."



		In a hydrogen bond a hydrogen atom joined to an electronegative atom, such as nitrogen or oxygen, becomes partially positively charged, and is weakly attracted to another electronegative atom on a neighboring molecule.



		The strongest known noncovalent bond is the superbond that is formed between avidin, a protein found in egg white, and the growth factor biotin. It is almost impossible to separate the two molecules once bonded. The superbond is used in a number of biomedical research applications.



		*formulas and equations*



		Symbols are used to denote the elements. The symbol is usually the first letter or letters of the English or Latin name of the element—for example, C for carbon; Ca for calcium; Fe for iron (ferrum). These symbols represent one atom of the element; molecules containing more than one atom of an element are denoted by a subscript figure—for example, water is H₂O. In some substances a group of atoms acts as a single entity, and these are enclosed in parentheses in the symbol—for example (NH₄)₂SO₄denotes ammonium sulfate. The symbolic representation of a molecule is known as a formula. A figure placed before a formula represents the number of molecules of a substance taking part in, or being produced by, a chemical reaction—for example, 2H₂O indicates two molecules of water.



		Chemical reactions are expressed by means of equations. A chemical equation gives two basic pieces of information: (1) the reactants (on the left-hand side) and products (right-hand side); and (2) the reacting proportions (stoichiometry)—that is, how many units

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		of each reactant and product are involved. The equation must balance; that is, the total number of atoms of a particular element on the left-hand side must be the same as the number of atoms of that element on the right-hand side.



		This equation states that one molecule of sodium carbonate combines with two molecules of hydrochloric acid to form two molecules of sodium chloride, one of carbon dioxide, and one of water. Double arrows indicate that the reaction is reversible—in the formation of ammonia from hydrogen and nitrogen, the direction depends on the temperature and pressure of the reactants.



		Metals, Nonmetals, and the Periodic System



		Elements are divided into metals, which have luster and conduct heat and electricity, and nonmetals, which usually lack these properties. The periodic system, developed by John Newlands in 1863 and established by Dmitri Mendeleyev in 1869, classified elements according to their atomic weights. Those elements that resemble each other in general properties were found to bear a relation to one another by weight, and these were placed in groups or families. Certain anomalies in this system were later removed by classifying the elements according to their atomic numbers. The latter is equivalent to the positive charge on the nucleus of the atom.



		periodic table of the elements The periodic table of the elements arranges the elements into horizontal rows (called periods) and vertical columns (called groups) according to their atomic numbers. The elements in a group or column all have similar properties—for example, all the elements in the far right-hand column are inert gases.

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periodic table : first three periods



		To remember the elements in their correct order in the first three periods of the table (hydrogen being omitted and potassium included):



		Here lies Benjamin Bold cry not old friend needlessly Nature magnifies all simple people sometimes, clots and kings.



		helium, lithium, beryllium, boron, carbon, nitrogen, oxygen, fluorine, neon, sodium, magnesium, aluminum, silicon, phosphorus, sulfur, chlorine, argon, potassium



		Organic Chemistry



		Organic compounds, i.e. those based on linked carbon atoms, form the chemical basis of life and are more abundant than inorganic compounds. In a typical organic compound each carbon atom forms bonds covalently with each of its neighboring carbon atoms in a chain or ring, and additionally with other atoms, commonly hydrogen, oxygen, nitrogen, or sulfur.



		Many organic compounds (such as proteins and carbohydrates) are made only by living organisms, and it was once believed that organic compounds could not be made by any other means. This was disproved when Friedrich Wöhler synthesized urea in 1828, but the name "organic" (that is, "living") chemistry has remained in use. Many organic compounds are derived from petroleum, which represents the chemical remains of millions of microscopic marine organisms.



		In inorganic chemistry, a specific formula usually represents one substance only, but in organic chemistry, it is exceptional for a molecular formula to represent only one substance, owing to the different ways that carbon chains can be branched and interlinked. Different chemical compounds having the same molecular composition and mass as one another, but with different physical or chemical properties owing to the

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The Chemical Elements

An element is a substance that cannot be split chemically into simpler substances. The atoms of a particular element all have the same number of protons in their nuclei (their atomic number).
(– = not applicable.)

Name

Symbol

Atomic number

Atomic mass (amu)¹

Relative density²

Melting or fusing point (°C)



		(table continued on next page)

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		(table continued from previous page)

Name	Symbol	Atomic number	Atomic mass (amu)¹	Relative density²	Melting or fusing point (°C)
Mendelevium	Md	101	256³	–	–
Mercury	Hg	80	200.59	13.596	–38.9
Molybdenum	Mo	42	95.94	10.2	2,500
Neodymium	Nd	60	144.24	6.96	840
Neon	Ne	10	20.179	gas	–248.6
Neptunium	Np	93	237³	–	–
Nickel	Ni	28	58.71	8.9	1,452
Niobium	Nb	41	92.9064	8.4	1,950
Nitrogen	N	7	14.0067	gas	–211
Nobelium	No	102	254³	–	–
Osmium	Os	76	190.2	22.48	2,700
Oxygen	O	8	15.9994	gas	–227
Palladium	Pd	46	106.4	11.4	1,549
Phosphorus	P	15	30.9738	1.8–2.3	44
Platinum	Pt	78	195.09	21.5	1,755
Plutonium	Pu	94	242³	–	–
Polonium	Po	84	210³	–	–
Potassium	K	19	39.102	0.87	63
Praseodymium	Pr	59	140.9077	6.48	940
Promethium	Pm	61	145³	–	–
Protactinium	Pa	91	231.0359	–	–
Radium	Ra	88	226.0254	6.0	700
Radon	Rn	86	222³	gas	–150
Rhenium	Re	75	186.2	21	3,000
Rhodium	Rh	45	102.9055	12.1	1,950
Rubidium	Rb	37	85.4678	1.52	39
Ruthenium	Ru	44	101.07	12.26	2,400
Rutherfordium	Rf	104	262³	–	–
Samarium	Sm	62	150.4	7.7	1,350
Scandium	Sc	21	44.9559	–	–
Seaborgium	Sg	106	263³	–	–
Selenium	Se	34	78.96	4.5	170–220
Silicon	Si	14	28.086	2.0–2.4	1,370
Silver	Ag	47	107.868	10.5	960
Sodium	Na	11	22.9898	0.978	97
Strontium	Sr	38	87.62	2.54	800
Sulfur	S	16	32.06	2.07	115–119
Tantalum	Ta	73	180.9479	16.6	2,900
Technetium	Tc	43	99³	–	–
Tellurium	Te	52	127.60	6.0	446
Terbium	Tb	65	158.9254	–	–
Thallium	TI	81	204.37	11.85	302
Thorium	Th	90	232.0381	11.00	1,750
Thulium	Tm	69	168.9342	–	–
Tin	Sn	50	118.69	7.3	232
Titanium	Ti	22	47.90	4.54	1,850
Tungsten	W	74	183.85	19.1	2,900–3,000
Ununnilium	Uun⁴	110	269³	–	–
Unununium	Uuu⁴	111	272³	–	–
Uranium	U	92	238.029	18.7	–
Vanadium	V	23	50.9414	5.5	1,710
Xenon	Xe	54	131.30	gas	–140
Ytterbium	Yb	70	173.04	–	–
Yttrium	Y	39	88.9059	3.8	–
Zinc	Zn	30	65.37	7.12	418
Zirconium	Zr	40	91.22	4.15	2,130
¹ Atomic mass units.
² Also known as specific gravity.
³ The number given is that for the most stable isotope of the element.
⁴ Elements as yet unnamed; temporary identification assigned until a name is approved by the International Union of Pure and Applied Chemistry.

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		different structural arrangement of the constituent atoms are known as isomers. For example, the organic compounds butane (CH₃(CH₂)₂CH₃) and methyl propane (CH₃CH(CH₃)CH₃) are isomers, each possessing four carbon atoms and ten hydrogen atoms but differing in the way that these are arranged with respect to each other. Structural isomers such as these obviously have different constructions, but geometrical and optical isomers must be drawn or modeled in order to appreciate the difference in their three-dimensional arrangement. Geometrical isomers have a plane of symmetry and arise because of the restricted rotation of atoms around a bond; optical isomers are mirror images of each other. For instance, 1,1-dichloroethene (CH₂=CCl₂) and 1,2-dichloroethene (CHCl=CHCl) are structural isomers, but there are two possible geometric isomers of the latter (depending on whether the chlorine atoms are on the same side or on opposite sides of the plane of the carbon–carbon double bond).



		isomer The chemicals butane and methyl propane are isomers. Each has the molecular formula CH₃CH(CH₃)CH₃, but with different spatial arrangements of atoms in theirmolecules.



		Hydrocarbons form one of the most prolific of the many organic types; fuel oils are largely made up of hydrocarbons. Typical groups containing only carbon, hydrogen, and oxygen are alcohols, aldehydes, ketones, ethers, esters, and carbohydrates. Among groups containing nitrogen are amides, amines, nitrocompounds, amino acids, proteins, purines, alkaloids, and many others, both natural and artificial. Other organic types contain sulfur, phosphorus, or halogen elements.



		The basis of organic chemistry is the ability of carbon to form long chains of atoms, branching chains, rings, and other complex structures. Compounds containing only carbon and hydrogen are known as hydrocarbons. Carbon bonds to adjacent atoms covalently.



		In a covalent bond two atoms share one or more pairs of electrons (usually each atom contributes an electron). The bond is often represented by a single line drawn between the two atoms. Double bonds, seen, for example, in the alkenes, are formed when two atoms share two pairs of electrons (the atoms usually



		aromatic compound Compounds whose molecules contain the benzene ring, or variations of it, are called aromatic. The term was originally used to distinguish sweet-smelling compounds from others.

Page 71



		contribute a pair each); triple bonds, seen in the alkynes, are formed when atoms share three pairs of electrons. Such bonds are represented by a double or triple line, respectively, between the atoms concerned. Covalent compounds have the following general properties: they have low melting and boiling points; never conduct electricity; and are usually insoluble in water and soluble in organic solvents.



		*homologous series* Organic chemistry is largely the chemistry of a great variety of homologous series—those in which the molecular formulas, when arranged in ascending order, form an arithmetical progression. The physical properties undergo a gradual change from one member to the next.



		The linking carbon atoms that form the backbone of an organic molecule may be built up from beginning to end without branching, or may throw off branches at one or more points. Sometimes the ropes of carbon atoms curl round and form rings (cyclic compounds), usually of five, six, or seven atoms. Open-chain and cyclic compounds may be classified as aliphatic or aromatic depending on the nature of the bonds between their atoms. Compounds containing oxygen, sulfur, or nitrogen within a carbon ring are called heterocyclic compounds.



		Organic chemical compounds in which the carbon atoms are joined in straight chains, as in hexane (C₆H₁₄), or in branched chains, as in 2-methylpentane (CH₃CH(CH₃)CH₂CH₂CH₃) are known as aliphatic compounds. Aliphatic compounds have bonding electrons localized within the vicinity of the bonded atoms. Cyclic compounds that do not have delocalized electrons are also aliphatic, as in the alicyclic compound cyclohexane (C₆H₁₂) or the heterocyclic piperidine (C₅H₁₁N).



		Among the principal aliphatic compounds are the alkanes (paraffins), which include methane, ethane, pentane, gasoline, kerosene, lubricating oil, and paraffin wax; the alkenes (olefins), including ethylene (C₂H₄); the ethynes; the alcohols, ethers, ethanoic and other acids, esters, certain classes of amines, the carbohydrates, such as starch, sugar, and cellulose; and the fats.



		In aromatic compounds some of the bonding electrons are delocalized (shared among several atoms within the molecule and not localized in the vicinity of the atoms involved in bonding). The commonest aromatic compounds have ring structures, the atoms comprising the ring being either all carbon or containing one or more different atoms (usually nitrogen, sulfur, or oxygen). Typical examples are benzene (C₆H₆) and pyridine (C₆H₅N).



		The most fundamental of all natural processes are oxidation, reduction, hydrolysis, condensation, polymerization, and molecular rearrangement. In nature, such changes are often brought about through the agency of promoters known as enzymes, which act as catalytic agents in promoting specific reactions. The most fundamental of all natural processes is synthesis, or building up. In living plant and animal organisms the energy stored in carbohydrate molecules, derived originally from sunlight, is released by slow oxidation and utilized by the organisms. The complex carbohydrates thereby revert to carbon dioxide and water, from where they were built up with absorption of energy. Thus, a carbon food cycle exists in nature. In a corresponding nitrogen food cycle, complex proteins are synthesized in nature from carbon dioxide, water, soil nitrates, and ammonium salts, and these proteins ultimately revert to the elementary raw materials from which they came, with the discharge of their energy of chemical combination.



		*polymer* A compound made up of a large long-chain or branching matrix composed of many repeated



		polymerization In polymerization small molecules (monomers) join together to make large molecules (polymers). In the polymerization of ethene to polyethene, electrons are transferred from the carbon–carbon double bond of the ethene molecule, allowing the molecules to join together as a long chain of carbon–carbon single bonds.

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		simple units (monomers) linked together by polymerization. There are many polymers, both natural (cellulose, chitin, lignin) and synthetic (polyethylene and nylon, types of plastic). Synthetic polymers belong to two groups: thermosoftening and thermosetting.



		The size of the polymer matrix is determined by the amount of monomer used; it therefore does not form a molecule of constant molecular size or mass.

Polymers and Liquid Crystals
http://plc.cwru.edu/

Online tutorial about two modern physical wonders. The site is divided into a "virtual textbook" and a "virtual laboratory," with corresponding explanations and experiments.



		*some important organic compounds*



		*alcohols*



		These are organic compounds characterized by the presence of one or more OH (hydroxyl) groups in the molecule, and which form esters with acids. The main uses of alcohols are as solvents for gums, resins, lacquers, and varnishes; in the making of dyes; for essential oils in perfumery; and for medical substances in pharmacy. The alcohol produced naturally in the fermentation process and consumed as part of alcoholic beverages is called ethanol.



		Alcohols may be liquids or solids, according to the size and complexity of the molecule. The five simplest alcohols form a series in which the number of carbon and hydrogen atoms increases progressively, each one having an extra CH₂ (methylene) group in the molecule: methanol or wood spirit (methyl alcohol, CH₃OH); ethanol (ethyl alcohol, C₂H₅OH); propanol (propyl alcohol, C₃H₇OH); butanol (butyl alcohol, C₄H₉OH); and pentanol (amyl alcohol, C₅H₁₁OH). The lower alcohols are liquids that mix with water; the higher alcohols, such as pentanol, are oily liquids immiscible with water; and the highest are waxy solids—for example, hexadecanol (cetyl alcohol, C₁₆H₃₃OH) and melissyl alcohol (C₃₀H₆₁OH), which occur in sperm-whale oil and beeswax, respectively. Alcohols containing the CH₂OH group are primary; those containing CHOH are secondary; while those containing COH are tertiary.



		*aldehydes* Aldehydes are prepared by oxidation of primary alcohols, so that the OH (hydroxyl) group loses its hydrogen to give an oxygen joined by a double bond to a carbon atom (the aldehyde group, with the formula CHO).



		The name is made up from alcohol dehydrogenation—that is, alcohol from which hydrogen has been removed. Aldehydes are usually liquids and include methanal (formaldehyde), ethanal (acetaldehyde), and benzaldehyde.



		*alkanes* Alkanes are molecules with the general formula C_nH_2n+2, and used to be known as paraffins. As they contain only single covalent bonds, alkanes are said to be saturated. Lighter alkanes, such as methane, ethane, propane, and butane, are colorless gases; heavier ones are liquids or solids. In nature they are found in natural gas and petroleum. Their principal reactions are combustion and bromination.

methane



		The flatulence of a single sheep could power a small truck for 40 km/25 mi a day. The digestive process produces methane gas, which can be burned as fuel. According to one New Zealand scientist, the methane from 72 million sheep could supply the entire fuel needs of his country.



		*alkenes* Alkenes are members of the group of hydrocarbons having the general formula C_nH_2n, formerly known as olefins. Alkenes are unsaturated compounds, characterized by one or more double bonds between adjacent carbon atoms. Lighter alkenes, such as ethene and propene, are gases, obtained from the cracking of oil fractions. Alkenes react by addition, and many useful compounds, such as polyethene and bromoethane, are made from them.



		*alkynes* Alkynes are hydrocarbons with the general formula C_nH_2n _–2 are known as alkynes (formerly acetylenes). They are unsaturated compounds, characterized by one or more triple bonds between adjacent carbon atoms. Lighter alkynes, such as ethyne, are gases; heavier ones are liquids or solids.

organic chemistry



		To remember the prefixes for naming carbon chains:



		Met Ethel properly but my pants had holes (Meth, eth, prop, but, pent, hex, hept)



		*amides* Amides are organic chemicals derived from a carboxylic acid (fatty acid) by the replacement of the hydroxyl group (OH) with an amino group (NH₂). One of the simplest amides is acetamide (CH₃CONH₂), which has a strong mousy odor.



		*amines* Amines are a class of organic chemical compounds in which one or more of the hydrogen atoms of ammonia (NH₃) have been replaced by other groups of atoms. Methyl amines have unpleasant ammonia odors and occur in decomposing fish. They are all

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		alkanes The lighter alkanes methane, ethane, propane, and butane, showing the aliphatic chains, where a hydrogen atom bonds to a carbon atom at all available sites.



		gases at ordinary temperature. Aromatic amine compounds include aniline, which is used in dyeing.



		*amino acids* Amino acids are the basic building blocks of life, being a vital constituent of proteins. They have a carboxyl group (COOH) and an amino group (NH₂) joined to the same carbon atom, and have the general formula RCHNH₂(COOH). Their biological versitility derives from the fact that they have both acidic and basic properties. Peptides are molecules comprising two or more amino acid molecules (not necessarily different) joined by peptide bonds, whereby the acid group of one acid is linked to the amino group of the other (–CO.NH). The number of amino acid molecules in the peptide is indicated by referring to it as a di-, tri-, or polypeptide (two, three, or many amino acids).



		organic chemistry Common organic molecule groupings. Organic chemistry is the study of carbon compounds, which make up over 90% of all chemical compounds. This diversity arises because carbon atoms can combine in many different ways with other atoms, forming a wide variety of loops and chains.



		*carboxylic acids* Carboxylic acids (fatty acids) contain the carboxyl group COOH. They are weak acids which occur widely throughout nature. The simplest and best-known carboxylic acid is acetic acid, or vinegar, which has the formula CH₃COOH.



		*esters* Esters are organic compounds formed by the reaction between an alcohol and an organic acid, with the elimination of water. Unlike salts, esters are covalent compounds.

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		amino acid Amino acids are natural organic compounds that make up proteins and can thus be considered the basic molecules of life. There are 20 different common amino acids. They consist mainly of carbon, oxygen, hydrogen, and nitrogen. Each amino acid has a common core structure (consisting of two carbon atoms, two oxygen atoms, a nitrogen atom, and four hydrogen atoms) to which is attached a variable group, known as the R group. In glycine, the R group is a single hydrogen atom; in alanine, the R group consists of a carbon and three hydrogen atoms.



		*ethers* Ethers are organic compounds with an oxygen atom linking the carbon atoms of two hydrocarbon radical groups (general formula R-O-R[prime]); also the common name for ethoxyethane C₂H₅OC₂H₅(also called diethyl ether). This is used as an anesthetic and as an external cleansing agent before surgical operations. It is also used as a solvent, and in the extraction of oils, fats, waxes, resins, and alkaloids.



		Ethoxyethane is a colorless, volatile, inflammable liquid, slightly soluble in water, and miscible with ethanol. It is prepared by treatment of ethanol with excess concentrated sulfuric acid at 140°C/284°F.



		ester Molecular model of the ester ethyl ethanoate (ethyl acetate) CH₃CH₂COOCH₃.



		*ketones* Ketones contain the carbonyl group (C=O) bonded to two atoms of carbon (instead of one carbon and one hydrogen as in aldehydes). They are liquids or low-melting-point solids, slightly soluble in water, often having a sweet smell. An example is propanone (acetone, CH₃COCH₃), which is used as a solvent.



		*gasoline*



		Gasoline is a mixture of hydrocarbons derived from petroleum, mainly used as a fuel for internal-combustion engines. It is colorless and highly volatile. Leaded gasoline contains antiknock (a mixture of tetraethyl lead and dibromoethane), which improves the combustion of gasoline and the performance of a car engine. The lead from the exhaust fumes enters the atmosphere, mostly as simple lead compounds. There is strong evidence that it can act as a nerve poison on young children and cause mental impairment. This has prompted a switch to the use of unleaded gasoline in the United States.



		*petroleum or crude oil* natural mineral oil, a thick greenish-brown flammable liquid found underground in permeable rocks. Petroleum consists of hydrocarbons mixed with oxygen, sulfur, nitrogen, and other elements in varying proportions. It is thought to be derived from ancient organic material that has been converted by, first, bacterial action, then heat, and pressure (but its origin may be chemical also).



		From crude petroleum, various products are made

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		by distillation and other processes; for example, fuel oil, gasoline, kerosene, diesel, and lubricating oil. Petroleum products and chemicals are used in large quantities in the manufacture of detergents, artificial fibers, plastics, insecticides, fertilizers, pharmaceuticals, toiletries, and synthetic rubber.



		Inorganic Chemistry



		Inorganic chemistry is the branch of chemistry that deals with the chemical properties of the elements and their compounds, excluding the more complex covalent compounds of carbon, which are considered in organic chemistry. The origins of inorganic chemistry lay in observing the characteristics and experimenting with the uses of the substances (compounds and elements) that could be extracted from mineral ores. These could be classified according to their chemical properties: elements could be classified as metals or nonmetals; compounds as acids or bases, oxidizing or reducing agents, ionic compounds (such as salts), or covalent compounds (such as gases).

Web Elements
http://www.shef.ac.uk/~chem/web-elements/web-elements-home.html

Periodic table on the Web, with 12 different categories of information available for each element—from its physical and chemical characteristics to its electronic configuration.



		Elements are classified as metals, nonmetals, or metalloids (weakly metallic elements) depending on a combination of their physical and chemical properties; about 75% are metallic. Some elements occur abundantly (oxygen, aluminum); others occur moderately or rarely (chromium, neon); some, in particular the radioactive ones, are found in minute (neptunium, plutonium) or very minute (technetium) amounts.



		Symbols (devised by Swedish chemist Jöns Berzelius) are used to denote the elements; the symbol is usually the first letter or letters of the English or Latin name (for example, C for carbon, Ca for calcium, Fe for iron, from the Latin ferrum). The symbol represents one atom of the element.



		According to current theories, hydrogen and helium were produced in the Big Bang at the beginning of the universe. Of the other elements, those up to atomic number 26 (iron) are made by nuclear fusion within the stars. The more massive elements, such as lead and uranium, are produced when an old star explodes; as its center collapses, the gravitational energy squashes nuclei together to make new elements.



		The arrangement of elements into groups possessing similar properties led to Mendeleyev's periodic table of the elements, which prompted chemists to predict the properties of undiscovered elements that might occupy gaps in the table. This, in turn, led to the discovery of new elements, including a number of highly radioactive elements that do not occur naturally.



		The periodic table today is the most recognizable logo of chemistry. Despite the range of formats they are all related to Mendeleyev's original formulation.

Elementistory
http://smallfry.dmu.ac.uk/chem/periodic/elementi.html

Periodic table of elements showing historical rather than scientific information. The contents under the chemical links in the table are mainly brief in nature, commonly just giving names and dates of discovery.



		*metals*



		Metallic elements comprise about 75% of the 112 elements in the periodic table of the elements. Physical properties include a sonorous tone when struck, good conduction of heat and electricity, opacity but good reflection of light, malleability, which enables them to be cold-worked and rolled into sheets, ductility, which permits them to be drawn into thin wires, and the possible emission of electrons when heated (thermionic effect) or when the surface is struck by light (photoelectric effect).



		The majority of metals are found in nature in a combined form only, as compounds or mineral ores; about 16 of them also occur in the elemental form, as native metals. Their chemical properties are largely determined by the extent to which their atoms can lose one or more electrons and form positive ions (cations).



		In a metal the valence (bonding) electrons are able to move within the crystal and these electrons are said to be delocalized. Their movement creates short-lived, positively charged ions. The electrostatic attraction between the delocalized electrons and the ceaselessly forming ions constitutes the metallic bond.



		The following metals are widely used in commerce: precious metals—gold, silver, and platinum, used principally in jewelry; heavy metals—iron, copper, zinc, tin, and lead, the common metals of engineering; rarer heavy metals—nickel, cadmium, chromium, tungsten, molybdenum, manganese, cobalt, vanadium, antimony, and bismuth, used principally for alloying with the heavy metals; light metals—aluminum and magnesium; alkali metals—sodium, potassium, and lithium; and alkaline-earth metals—calcium, barium, and strontium, used principally for chemical purposes.



		Other metals have come to the fore because of special nuclear requirements—for example, technetium,

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The Periodic Table

By Gordon Woods

Think how difficult it would be to assemble a jigsaw of which about 35 of the pieces were missing and roughly 20 of the 65 you had were too damaged to fit properly. Could you work out the shapes of some of the missing pieces? This is exactly what Mendeleyev did in 1869 when he produced the first periodic table.
Several 19th-century scientists had sought earlier to identify patterns in the properties of chemical elements linked to the weights of the atoms. Dobereiner had noticed sets of three similar elements (triads) for which the average weight of the lightest and heaviest was close to the weight of the middle one (try chlorine 35.5, bromine 80, and iodine 127). British chemist Newlands wrote the elements in order of increasing weight, noting that an element resembled the eight following. His ''Law of Octaves" soon broke down because of missing elements from a fundamentally correct law. He was ridiculed (why not list the elements alphabetically!), flung out of the Royal Society, Britain's top scientific institution, only to be reinstated when it was realized that he had nearly beaten Mendeleyev.

who was Mendeleyev?

Dmitri Ivanovitch Mendeleyev was born in Tobolsk (Siberia) in 1834 and brought to St Petersburg, capital of czarist Russia, for his secondary education by his ambitious mother who had realized her youngest son's potential. After research throughout Europe he was appointed chemistry professor at St. Petersburg in 1865. His first marriage foundered because of all the time he spent researching; later he married a young student. After discontent among the university students Mendeleyev took their petition to the education minister who fired him from his professorial chair. Later both Oxford and Cambridge awarded him honorary doctorates. Aged 53 he made a solo balloon ascent to view a solar eclipse. A Periodic Table was carried aloft in his funeral procession in February 1907.
Mendeleyev is said to have been playing patience when he suddenly visualized the arrangement of the elements in the patterns of the cards. It is certainly true that 20 years previous education had equipped him to formulate the "Periodic Law" which he developed for the remaining 40 years of his life, It stated that the elements display periodic (i.e. regularly repeating) properties when listed in order of increasing atomic weight.
Accurate atomic weights were needed for all 19th-century element patterns. Mendeleyev correctly recalculated some values better to fit his table. However iodine and tellurium provided a problem since iodine was chemically similar to bromine yet the heavier element tellurium fitted below bromine according to the weight order. Mendeleyev's solution was to have his research assistants redetermine tellurium's atomic weight to be the smaller. Thus he correctly positioned the two elements but for the wrong reason. Today we know that the elements are listed in order of increasing atomic number which only differs from the atomic weight order in three instances.
A stroke of genius was to leave spaces for elements yet to be discovered and to boldly predict properties for five such elements. Good scientists explain known information, great ones correctly predict unknown facts. Fortunately three of these missing elements were found within 20 years and their properties matched predictions to a remarkable degree.

modern periodic tables

Note the plural. There are many different formats, some are three dimensional but all show the elements in order of increasing atomic number. Most have vertical columns called groups and horizontal rows called periods. The underlying reason for the arrangement is the electron arrangement of the atoms of the elements. All elements in the same group have the same number of electrons in the outermost shell which governs the chemical nature of an element, hence their chemical similarity. Elements in the same period have the same number of electron shells, an extra electron being added for each increase in the atomic number.

metals and nonmetals

Crossing from left to right elements become more nonmetallic and descending they become more metallic. Thus moving diagonally down to the right, elements are comparable in their metallic/nonmetallic nature. This can be shown by a staircase, or better, as a diagonal line through the boxes of those elements which cannot be clearly classified either as a metal or a nonmetal. For example the use of silicon in computers stems from it being a semiconductor. Metals are conductors, nonmetals are insulators, so semiconductors are both. Science is not black and white but shades of gray.
One can copy Mendeleyev's work by making predictions about "unknown" elements. Knowing that both sodium and potassium react with water producing hydrogen and an alkali, it is reasonable to predict the same behavior for rubidium and cesium directly below them. Since potassium is more reactive than sodium, It is likely that cesium will be the most reactive of the four. It is! When added to a bowl of water it shatters the container! Incidentally cesium is one of three elements which have a different spelling in North America and the UK. Which are the others?

are there more elements to discover?

By 1950 all the elements for which Mendeleyev had left gaps had been discovered. Some are extremely rare and were identified from the radioactive decay of other elements, sometimes in the debris of atomic bomb tests (1944–50). However, elements with atomic numbers above 92 have been created by bombarding atoms of uranium with neutrons, carbon nuclei, and other subatomic particles. These synthetic elements are all identified from their radioactivity. As the atomic number increases it becomes harder to make the elements, so less of the element exists . . . and it is decaying all the time. It is possible to identify 10–18 g but there is less than 1 g of the elements with atomic number greater than 100.
The discoverer of an element has the right to name it. Some chose their country (gallium, francium), or a property (chromium has compounds in many colors), or the place of discovery (such as strontium, named after the Scottish village of Strontian). Only three places in the world have the facilities to make the

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synthetic elements. Both the USSR and the USA claimed initial discovery of elements 104 and 105 but each country gave them different names (for example 104 to the Russians was Kurschatovium (Ku) but to the Americans was rutherfordium (Rf)). This scientific argument was initially solved by giving them artificial temporary names, unnilquadium (a hundredandfourium) and unnilpentium. A committee sat for years to decide officially who were the discoverers.

symbols and names

Element symbols are internationally agreed but the name differs with the language. This difference is only slight with elements discovered since 1850. Less reactive metals, isolated for hundreds of years may have very different names. Gasoline is unleaded in the UK, bleifrei in Germany, sans plomb in France, senza piomba in Italy, sin plomo in Spain. Note how the last three names relate to the Latin plumbum from which the symbol Pb is derived, as are plumber and plumbline.

unusual formats

Hundreds of versions exist of the periodic table. For example, some show the physical state (solid, liquid, or gas) of the element (in the UK only, the metal mercury and the nonmetal bromine are liquids) and three-dimensional varieties divide up the periodic table into its four blocks labeled s, p, d, and f according to the shape of the outer electron cloud round the nucleus.



		produced in nuclear reactors, is corrosion-inhibiting; zirconium may replace aluminum and magnesium alloy in canning uranium in reactors.



		*reactions of metals with acids* Metals replace the hydrogen in an acid to form a salt. For example, with magnesium and sulfuric acid the products are magnesium sulfate and hydrogen:



		Most metals form oxides. For example magnesium will react with oxygen to form magnesium oxide:



		Some metals displace hydrogen in water to form hydroxides or oxides. For example when sodium is added to water sodium hydroxide is formed and hydrogen is given off:



		All metals except mercury are solid at ordinary temperatures, and all of them will crystallize under suitable conditions. The chief chemical properties of metals also include their strong affinity for certain nonmetallic elements, for example sulfur and chlorine, with which they form sulfides and chlorides. Metals will, when fused, enter into the forming of alloys.



		Metals have been put to many uses since prehistoric times, both structural and decorative, and the Copper Age, Bronze Age, and Iron Age are named for the metal that formed the technological base for that stage of human evolution. The science and technology of producing metals is called metallurgy.



		*alkali metals* The alkili metals form a linked group (Group One) in the periodic table of the elements. They comprise six metallic elements with similar chemical properties: lithium, sodium, potassium, rubidium, cesium, and francium. They are univalent (have a valence of one) and of very low density (lithium, sodium, and potassium float on water); in general they are reactive, soft, low-melting-point metals. Because of their reactivity they are only found as compounds in nature.

Flame Test

The flame test is a laboratory method used to ascertain the presence of positive ions in a sample. The sample is moistened with sulfuric acid and held in a Bunsen flame; the color of the flame that results indicates which ions are present.

copper, thallium, boron (boric acid)

bright green

lead, arsenic, antimony

livid blue

copper (copper (II) chloride)

bright blue



		*sodium* Sodium is a soft, waxlike, silver-white, metal (symbol Na from Latin natrium). It has a very low density, being light enough to float on water. It is the sixth most abundant element (the fourth most abundant metal) in the earth's crust. Sodium is highly reactive, oxidizing rapidly when exposed to air and reacting violently with water. Sodium is important in the nervous systems of animals.



		Its most familiar compound is sodium chloride (common salt), which occurs naturally in the oceans and in salt deposits left by dried-up ancient seas.



		Other sodium compounds used industrially include sodium hydroxide (caustic soda, NaOH), sodium

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		carbonate (washing soda, Na₂CO₃) and hydrogencarbonate (sodium bicarbonate, NaHCO₃), sodium nitrate (saltpeter, NaNO₃, used as a fertilizer), and sodium thiosulfate (hypo, Na₂S₂O₃, used as a photographic fixer). Thousands of tons of these are manufactured annually. Sodium metal is used to a limited extent in spectroscopy, in discharge lamps, and alloyed with potassium as a heat-transfer medium in nuclear reactors. It was isolated from caustic soda in 1807 by English chemist Humphry Davy.



		*potassium* Potassium (symbol K from Latin kalium) is physically similar to sodium and it undergoes similar chemical reactions. It also has a very low density and is the second lightest metal (after lithium). It oxidizes rapidly when exposed to air and reacts violently with water. Of great abundance in the earth's crust, it is widely distributed with other elements and is found in salt and mineral deposits in the form of potassium aluminium silicates. Potassium is the main base ion of the fluid in the body's cells. Along with sodium, it is important to the electrical potential of the nervous system and, therefore, for the efficient functioning of nerve and muscle. Shortage, which may occur with excessive fluid loss (prolonged diarrhea, vomiting), may lead to muscular paralysis; potassium overload may result in cardiac arrest. It is also required by plants for growth. The element was discovered and named in 1807 by Humphry Davy, who isolated it from potash in the first instance of a metal being isolated by electric current.

Davy Discovers Sodium and Potassium
http://dbhs.wvusd.k12.ca.us/Chem-History/Davy-Na&K-1808.html

Davy's paper to the Royal Society in 1808 titled "On some new phenomena of chemical changes produced by electricity, particularly the decomposition of fixed alkalies, and the exhibition of the new substances which constitute their bases: and on the general nature of alkaline bodies." Quite apart from it being the longest title ever, it seems astounding that only 190 years ago humankind did not know that common salt was sodium chloride, this paper marking the leap in knowledge which created a century of chemical discoveries.



		*alkaline-earth metals* The six metals belonging to Group Two in the periodic table of the elements are termed alkaline-earth metals. Beryllium, magnesium, calcium, strontium, barium, and radium have similar bonding properties. They are strongly basic (see base), bivalent (have a valence of two), and occur in nature only in compounds. They and their compounds are used to make alloys, oxidizers, and drying agents. Examples of alkaline-earth metals are given below.



		*calcium* Calcium is (Latin calcis, "lime") a soft, silvery-white metallic element, symbol Ca. It is the fifth most abundant element (the third most abundant metal) in the earth's crust, and is found mainly as its carbonate CaCO₃, which occurs in a fairly pure condition as chalk and limestone (see calcite). Calcium is an essential component of bones, teeth, shells, milk, and leaves, and it forms 1.5% of the human body by mass. Calcium ions in animal cells are involved in regulating muscle contraction, blood clotting, hormone secretion, digestion, and glycogen metabolism in the liver. It is acquired mainly from milk and cheese, and its uptake is facilitated by vitamin D. Calcium deficiency leads to chronic muscle spasms (tetany); an excess of calcium may lead to the formation of stones in the kidney or gall bladder.



		The element was discovered and named by Humphry Davy in 1808. Its compounds include slaked lime (calcium hydroxide, Ca(OH)₂); plaster of Paris (calcium sulfate, CaSO₄.2H₂O); calcium phosphate (Ca₃(PO₄)₂), the main constituent of animal bones; calcium hypochlorite (CaOCl₂), a bleaching agent; calcium nitrate (Ca(NO)₂.4H₂O), a nitrogenous fertilizer; calcium carbide (CaC₂), which reacts with water to give ethyne (acetylene); calcium cyanamide (CaCN₂), the basis of many pharmaceuticals, fertilizers, and plastics, including melamine; calcium cyanide (Ca(CN)₂), used in the extraction of gold and silver and in electroplating; and others used in baking powders and fillers for paints.



		*magnesium* Magnesium is a lightweight, very ductile and malleable, silver-white, metallic element (symbol Mg). It is the lightest of the commonly used metals. Magnesium silicate, carbonate, and chloride are widely distributed in nature. The metal is used in alloys and flash photography. It is a necessary trace element in the human diet, and green plants cannot grow without it since it is an essential constituent of the photosynthetic pigment chlorophyll (C₅₅H₇₂MgN₄O₅).



		It was named for the ancient Greek city of Magnesia, near where it was first found. It was first recognized as an element by Scottish chemist Joseph Black in 1755 and discovered in its oxide by English chemist Humphry Davy in 1808. Pure magnesium was isolated in 1828 by French chemist Antoine-Alexandre-Brutus Bussy.



		*strontium* Strontium is a soft, ductile, pale yellow, metallic element (symbol Sr). It is widely distributed in small quantities only as a sulfate or carbonate. Strontium salts burn with a crimson flame and are used in fireworks and signal flares. The radioactive isotopes Sr-89 and Sr-90 (half-life 25 years) are some of the most dangerous products of the nuclear industry; they are fission products in nuclear explosions and in the

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		reactors of nuclear power plants. Strontium is chemically similar to calcium and deposits in bones and other tissues, where the radioactivity is damaging. The element was named in 1808 by Humphry Davy, who isolated it by electrolysis, after Strontian, a mining location in Scotland where it was first found.



		*other important metals* A few of the more commonly used metals are listed below.



		*iron* Iron is a hard, malleable and ductile, silver-gray, metal (symbol Fe from Latin ferrum). It is the fourth most abundant element (the second most abundant metal, after aluminum) in the earth's crust. Iron occurs in concentrated deposits as the ores hematite (Fe₂O₃), spathic ore (FeCO₃), and magnetite (Fe₃O₄). It sometimes occurs as a free metal, occasionally as fragments of iron or iron-nickel meteorites.



		Iron is the most common and most useful of all metals; it is strongly magnetic and is the basis for steel, an alloy with carbon and other elements. In electrical equipment iron is used in all permanent magnets and electromagnets, and forms the cores of transformers and magnetic amplifiers. In the human body, iron is an essential component of hemoglobin, the molecule in red blood cells that transports oxygen to all parts of the body. A deficiency in the diet causes a form of anemia.



		Iron is a member of the group known as the transition metals. Transition metals bond in a more complex way than other metals, having the ability to bond covalently, and have more than one valence: in its compounds iron may exist as Fe(II) (e.g. FeCO₃) or Fe(III) (e.g. Fe₂O₃). Other transition metals include nickel, copper, and gold.



		basic-oxygen process The basic-oxygen process is the primary method used to produce steel. Oxygen is blown at high pressure through molten pig iron and scrap steel in a converter lined with basic refractory materials. The impurities, principally carbon, quickly burn out, producing steel.

transition metals



		To remember the first row of transition metals in the periodic table:



		Scandinavian TV corrupts many French coalmen's nieces and couzins



		(Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn)



		*aluminum* Aluminum is a lightweight, silver-white, ductile and malleable metallic element (symbol Al). It is the third most abundant element (and the most abundant metal) in the earth's crust, of which it makes up about 8.1% by mass. It is nonmagnetic, an excellent conductor of electricity, and oxidizes easily, the layer of oxide on its surface making it highly resistant to tarnish. Pure aluminum is a reactive element with stable compounds, so a great deal of energy is needed in order to separate aluminum from its ores, and the pure metal was not readily obtainable until the middle of the 19th century. Commercially, it is prepared by the electrolysis of alumina (aluminum oxide), which is obtained from the ore bauxite. In its pure state aluminum is a weak metal, but when combined with elements such as copper, silicon, or magnesium it forms alloys of great strength.



		Aluminum is widely used in the shipbuilding and aircraft industries because of its light weight (relative density 2.70). It is also used in making cooking utensils, cans for beer and soft drinks, and foil. It is much used in steel-cored overhead cables and for canning uranium slugs for nuclear reactors. Aluminum is an essential constituent in some magnetic materials; and, as a good conductor of electricity, is used as foil in electrical capacitors. A plastic form of aluminum, developed in 1976, which molds to any shape and extends to several times its original length, has uses in electronics, cars, and building construction.



		*commercial production* The method now used for its commercial production is the electrolysis of alumina. An iron pot, lined with carbon, is charged with cryolite and heated to about 800°C/1,470°F by the electric current. For the electrolysis, a bundle of carbon rods is used as the anode, while the pot itself forms the cathode. The oxygen liberated combines with the carbon of the anode to form carbon dioxide, while the aluminum falls to the bottom of the vessel.

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		More alumina is added and the process continued, the molten metal being drawn off from time to time.



		*copper* Copper is an orange-pink, very malleable and ductile transition metal (symbol Cu from Latin cuprum). It is used for its durability, pliability, high thermal and electrical conductivity, and resistance to corrosion. It was the first metal used systematically for tools by humans; when mined and worked into utensils it formed the technological basis for the Copper Age in prehistory. When alloyed with tin it forms bronze, which is stronger than pure copper and may hold a sharp edge; the systematic production and use of this alloy was the basis for the prehistoric Bronze Age. Brass, another hard copper alloy, includes zinc.



		*zinc* Zinc is a hard, brittle, bluish-white, metallic element (symbol Zn). The principal ore is sphalerite or zinc blende (zinc sulfide, ZnS). Zinc is hardly affected by air or moisture at ordinary temperatures; its chief uses are in alloys such as brass and in coating metals (for example, galvanized iron). Its compounds include zinc oxide, used in ointments (as an astringent) and cosmetics, paints, glass, and printing ink. Zinc is a transition metal.



		Zinc is an essential trace element in most animals; adult humans have 2–3 g/0.07–0.1 oz zinc in their bodies. There are more than 300 known enzymes that contain zinc. Zinc has been used as a component of brass since the Bronze Age, but it was not recognized as a separate metal until 1746, when it was described by German chemist Andreas Sigismund Marggraf (1709–1782). The name derives from the shape of the crystals on smelting. The zinc industry in Europe generates about 80,000 tons of zinc waste each year.



		*nickel* Nickel is a hard, malleable and ductile, silver-white transition metal (symbol Ni). It occurs in igneous rocks and as a free metal (native metal), occasionally occurring in fragments of iron-nickel meteorites. It is a component of the earth's core, which is held to consist principally of iron with some nickel. It has a high melting point, low electrical and thermal conductivity, and can be magnetized. It does not tarnish and therefore is much used for alloys, electroplating, and for coinage.



		It was discovered in 1751 by Swedish mineralogist Axel Cronstedt (1722–1765) and the name given as an abbreviated form of kopparnickel (Swedish for "false copper"), since the ore in which it is found resembles copper but yields none.



		*silver* Silver is a white, lustrous, extremely malleable and ductile transition metal (symbol Ag from Latin argentum). It occurs in nature in ores and as a free metal; the chief ores are sulfides, from which the metal is extracted by smelting with lead. It is one of the best metallic conductors of both heat and electricity; its most useful compounds are the chloride and bromide, which darken on exposure to light and are the basis of photographic emulsions.



		Silver is used ornamentally, for jewelry and tableware, for coinage, in electroplating, electrical contacts, and dentistry, and as a solder. It has been mined since prehistory; its name is an ancient non-Indo-European one, silubr, borrowed by the Germanic branch as silber.



		*gold* Gold is a heavy, yellow precious metal (symbol Au). It is unaffected by temperature changes and is highly resistant to acids. For manufacture, gold is alloyed with another strengthening metal (such as copper or silver), its purity being measured in carats on a scale of 24. It is a transition metal.



		In 1990 the three leading gold-producing countries were South Africa, 667 tons; United States, 325 tons; and Russia, 287 tons. In 1989 gold deposits were found in Greenland with an estimated yield of 12 metric tons per year.



		Gold occurs naturally in veins, but following erosion it can be transported and redeposited. It has long been valued for its durability, malleability, and ductility, and its uses include dentistry and jewelry. As it will not corrode, it is also used in the manufacture of electric contacts for computers and other electrical devices.



		A Japanese company produced a malleable form of gold in 1995, made of fine gold powder mixed with water and a secret binder. Designers can work with the putty in the same way as clay, but once the putty is fired (at 1,000°C/1,832°F), the water and binder evaporate, leaving the fused gold particles.



		*alloys*



		Some metals can be blended with some other metallic or nonmetallic substances to give them special qualities, such as resistance to corrosion, greater hardness, or tensile strength. Useful alloys include bronze, brass, cupronickel, duralumin, German silver, gunmetal, pewter, solder, steel, and stainless steel.



		Among the oldest alloys is bronze (mainly an alloy of copper and tin), the widespread use of which ushered in the Bronze Age. Complex alloys are now common; for example, in dentistry, where a cheaper alternative to gold is made of chromium, cobalt, molybdenum, and titanium. Among the most recent alloys are superplastics: alloys that can stretch to double their length at specific temperatures, permitting, for example, their injection into molds as easily as plastic.



		Alloys are usually made by melting the metals together. (Certain elements which will not melt

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		together, for example copper and graphite may be combined using techniques of powder metallurgy.) Before adding the alloying element to the principal metal in the molten state it is necessary to ensure that it is free from oxygen, which would otherwise react with the alloying element, reducing the amount which would be dissolved and so causing an error in the composition. For this purpose a deoxidizer is added; this is often another metal.



		Compositions made only for the purpose of melting with other metals to form alloys are called master alloys or foundry alloys. They are used to overcome the problems of alloying metals of widely differing melting points, or to facilitate closer control over the final composition, or as deoxidizers. Shape memory alloys are imprinted with a shape so that even after distortion, a threshold temperature will bring about a return to the original shape. Nitinol, an alloy of titanium and nickel, and brass are examples.



		*brass* Brass is a metal alloy of copper and zinc, with not more than 5% or 6% of other metals. The zinc content ranges from 20% to 45%, and the colour of brass varies accordingly from coppery to whitish yellow. Brasses are characterized by the ease with which they may be shaped and machined; they are strong and ductile, resist many forms of corrosion, and are used for electrical fittings, ammunition cases, screws, household fittings, and ornaments.



		*nonmetals*



		There are about 20 elements that have certain physical and chemical properties opposite to those of metals. Nonmetals accept electrons and are sometimes called electronegative elements. Nonmetals include the halogens, carbon, oxygen, sulfur, and phosphorus. Their typical reactions are given below.



		*reactions of nonmetals with acids and alkalis* Nonmetals do not react with dilute acids but may react with alkalis.



		*with air or oxygen* They form acidic or neutral oxides.



		*with chlorine* They react with chlorine gas to form covalent chlorides.



		*with reducing agents* Nonmetals act as oxidizing agents.

Chemistry of Carbon
http://cwis.nyu.edu/pages/mathmol/modules/carbon/carbon1.html

Introduction to carbon, the element at the heart of life as we know it. This site is illustrated throughout and explains the main basic forms of carbon and the importance of the way scientists choose to represent these various structures.



		*carbon* Carbon (Latin carbo, carbonaris "coal") is a nonmetallic element, atomic number 6 (symbol C). It occurs on its own as the allotropes diamond, graphite, and as fullerenes. (Allotropy is the property whereby an element can exist in two or more forms (allotropes), each possessing different physical properties but the same state of matter—gas, liquid, or solid.) Its compounds are found in carbonaceous rocks such as chalk and limestone, as carbon dioxide in the atmosphere, as hydrocarbons in petroleum, coal, and natural gas, and as a constituent of all organic substances.



		In its amorphous form, it is familiar as coal, charcoal, and soot. The atoms of carbon can link with one another in rings or chains, giving rise to innumerable complex compounds. Of the inorganic carbon compounds, the chief ones are carbon dioxide, a colorless gas formed when carbon is burned in an adequate supply of air; and carbon monoxide (CO), formed when carbon is oxidized in a limited supply of air. Carbon disulfide (CS₂) is a dense liquid with a sweetish odor. Another group of compounds is the carbon halides, including carbon tetrachloride (tetrachloromethane, CCl₄).

Nobel Prize in Chemistry 1996
http://www.nobel.se/announcement-96/chemistry96.html

Description of the discovery of fullerene carbon molecules that led to the award of the 1996 Nobel prize. The description on this page covers all the basic aspects of the discovery, including the historical background and brief biographical information on the chemists involved. The structure of the molecule is also shown in a diagram, and some of the chemistry used in their manufacture is also described here.



		When added to steel, carbon forms a wide range of alloys with useful properties. In pure form, it is used as a moderator in nuclear reactors; as colloidal graphite it is a good lubricant and, when deposited on a surface in a vacuum, reduces photoelectric and secondary emission of electrons. Carbon is used as a fuel in the form of coal or coke. The radioactive isotope

Page 82



		carbon-14 (half-life 5,730 years) is used as a tracer in biological research and in radiocarbon dating. Analysis of interstellar dust has led to the discovery of discrete carbon molecules, each containing 60 carbon atoms. The C₆₀ molecules have been named buckminster-fullerenes because of their structural similarity to the geodesic domes designed by U.S. architect and engineer Buckminster Fuller.



		*halogens* The halogens are a group of five nonmetallic elements with similar chemical bonding properties: fluorine, chlorine, bromine, iodine, and astatine. They form a linked group in the periodic table of the elements, descending from fluorine, the most reactive, to astatine, the least reactive. They combine directly with most metals to form salts, such as common salt (NaCl). Each halogen has seven electrons in its valence shell, which accounts for the chemical similarities displayed by the group.



		*chlorine*



		Chlorine (Greek chloros "green") is a greenish-yellow, gaseous, nonmetallic element with a pungent odor (symbol Cl). It is a member of the halogen group and is widely distributed, in combination with the alkali metals, as chlorates or chlorides.

chlorine



		Fritz Haber developed chlorine gas for use by the Germans in World War I. Unable to live with this, his wife committed suicide in 1915.



		Chlorine is obtained commercially by the electrolysis of concentrated brine and is an important bleaching agent and germicide, used for sterilizing both drinking water and swimming pools. As an oxidizing agent it finds many applications in organic chemistry.



		The pure gas (Cl₂) is a poison and was used in gas warfare in World War I, where its release seared the membranes of the nose, throat, and lungs, producing pneumonia. Chlorine is a component of chlorofluorocarbons (CFCs) and is partially responsible for the depletion of the ozone layer; it is released from the CFC molecule by the action of ultraviolet radiation in the upper atmosphere, making it available to react with and destroy the ozone. The concentration of chlorine in the atmosphere in 1997 reached just over three parts per billion. It is expected to reach its peak in 1999 and then start falling rapidly due to international action to curb ozone-destroying chemicals.



		Some typical reactions are given below.



		with metals When dry chlorine is passed over a heated metal, the chloride is formed.



		with nonmetals The same reaction occurs with certain nonmetals, when the dry gas is passed over the heated element.



		with compounds With water, chlorine forms a bleaching solution.



		Iron (II) salts are oxidized to iron (III) salts.



		Organic compounds undergo halogenation.



		Alkalis form chlorides, chlorates, and water.



		Other halogens are displaced in a redox reaction.

On a Combination of Oxymuriatic Gas and Oxygene Gas
http://dbhs.wvusd.kl2.ca.us/Chem-History/avy-Chlorine-1811.html

Transcript of Humphry Davy's submission to the Royal Society naming chlorine and labeling it as an element.



		*oxygen* Oxygen is a colorless, odorless, tasteless, nonmetallic, gaseous element (symbol O). It is the most abundant element in the earth's crust (almost 50% by mass), forms about 21% by volume of the atmosphere, and is present in combined form in water and many other substances. Oxygen is a byproduct of photosynthesis and the basis for respiration in plants and animals.



		Oxygen is very reactive and combines with all other elements except the inert gases and fluorine. It is present in carbon dioxide, silicon dioxide (quartz), iron ore, and calcium carbonate (limestone). As a gas it exists as a molecule composed of two atoms (O₂) or as ozone (O₃) a highly reactive pale blue gas with a penetrating odor. Ozone is an allotrope (see allotropy) of oxygen, made up of three atoms of oxygen. It is formed when the molecule of the stable form of oxygen (O₂) is split by ultraviolet radiation or electrical discharge. It forms the ozone layer in the

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		upper atmosphere, which protects life on Earth from ultraviolet rays, a cause of skin cancer.



		Oxygen is obtained for industrial use by the fractional distillation of liquid air, by the electrolysis of water, or by heating manganese (IV) oxide with potassium chlorate. It is essential for combustion, and is used with ethyne (acetylene) in high-temperature oxyacetylene welding and cutting torches.



		The element was first identified by English chemist Joseph Priestley in 1774 and independently in the same year by Swedish chemist Karl Scheel. It was named by French chemist Antoine Lavoisier in 1777.



		*inert gases* The elements helium, neon, argon, krypton, xenon, and radon are known as the inert (or noble) gases, so named because they were originally thought not to enter into any chemical reactions. This is now known to be incorrect: in 1962, xenon was made to combine with fluorine, and since then, compounds of argon, krypton, and radon with fluorine and/or oxygen have been described.



		The extreme unreactivity of the inert gases is due to the stability of their electronic structure. All the electron shells (energy levels) of inert gas atoms are full and, except for helium, they all have eight electrons in their outermost (valence) shell. The apparent stability of this electronic arrangement led to the formulation of the octet rule to explain the different types of chemical bond found in simple compounds.

Inert Gases: Electronic Structure

name

symbol

atomic number



		electronic arrangement

helium



		2.

neon



		2.8.

argon



		2.8.8.

krypton



		2.8.18.8.

xenon



		2.8.18.18.8.

radon



		2.8.18.32.18.8.

inert gases



		To remember the inert gases:



		He neatly arranges Kremlin executive ranks (helium, neon, argon, krypton, xenon, radon)



		*argon*



		Argon is grouped with the inert gases, since it was long believed not to react with other substances, but observations now indicate that it can be made to combine with boron fluoride to form compounds. It constitutes almost 1% of the earth's atmosphere, and was discovered in 1894 by British chemists John Rayleigh and William Ramsay after all oxygen and nitrogen had been removed chemically from a sample of air. It is colorless and odorless, and used in electric discharge tubes and argon lasers.



		*ions*



		An ion is an atom, or group of atoms, that is either positively charged (cation) or negatively charged (anion), as a result of the loss or gain of electrons during chemical reactions or exposure to certain forms of radiation. In solution or in the molten state, ionic compounds such as salts, acids, alkalis, and metal oxides conduct electricity. These compounds are known as electrolytes.

cation



		To remember that cations are atoms that have lost an electron:



		Cat lost an eye



		Ions are produced during electrolysis, for example the salt zinc chloride (ZnCl₂) dissociates into the positively charged Zn²⁺ and negatively charged Cl^– when electrolyzed.



		*tests for negative ions* The presence of negative ions can be determined by performing a number of different tests.



		bromide (Br^–): addition of dilute nitric acid to bromide solution immediately yields a whitish precipitate of silver bromide, which is partially soluble in concentrated ammonia solution, for example:



		carbonate (CO₃^2–): a solid carbonate treated with dilute hydrochloric acid gives off carbon dioxide gas, which turns limewater milky:



		chloride (Cl^–): treatment of a chloride with concentrated sulfuric acid produces colorless hydrogen chloride gas, which forms thick white fumes of ammonium chloride on mixing with gaseous ammonia:



		hydrogencarbonate (HCO^3–): heating a solution of a hydrogencarbonate produces carbon dioxide, which turns limewater milky:

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		Hydrogencarbonates react with dilute hydrochloric acid giving off carbon dioxide, in a similar way to carbonates.



		iodide (I^–): on addition of silver nitrate solution to an acidified solution of an iodide, a yellow precipitate of silver iodide is formed immediately, which is insoluble in ammonia solution:



		nitrate (NO₃^–): there are two tests for the nitrate ion in solution. Sodium hydroxide solution and aluminum powder (or Devarda's alloy, which contains aluminum) are added to a solution of the nitrate. The mixture is warmed and the ammonia gas produced turns red litmus paper blue:



		The brown ring test: an equal volume of iron(II) sulfate solution (acidified with dilute sulfuric acid) is added to the nitrate solution in a test tube. Concentrated sulfuric acid is carefully poured down the side of the test tube, so that it forms a separate layer at the bottom of the tube. A brown ring is formed at the junction of the two layers. This is FeSO₄.NO, which is produced by the reaction of nitrate ions to nitrogen monoxide by the iron(II) ions:



		Care should be taken with this test, as nitrites and bromides can give similar results.



		nitrite (NO^2–): addition of dilute sulfuric acid to a nitrite produces brown nitrogen dioxide gas, which turns blue litmus paper red without bleaching it. The solution turns pale blue. No heating is required.



		sulfate (SO₄^2–): addition of dilute hydrochloric acid and barium sulfate solution to a solution of a sulfate results in the immediate precipitation of barium sulfate:



		sulfide (S^2–): addition of dilute hydrochloric acid to a sulfide results in the production of colorless hydrogen sulfide gas, which smells of rotten eggs and turns lead nitrate (soaked into filter paper) black.



		sulfite (SO₃^2–): addition of dilute hydrochloric acid to a sulfite, with heating, produces colorless sulfur dioxide gas. This turns potassium dichromate from orange to green, but does not change the color of lead nitrate solution.



		Tests for common positive ions are given above in the Flame Test table.



		*free radicals* A free radical is an atom or molecule that has an unpaired electron and is therefore highly reactive. Most free radicals are very short-lived. They are byproducts of normal cell chemistry and rapidly oxidize other molecules they encounter. Free radicals are thought to do considerable damage. They are neutralized by protective enzymes.



		Free radicals are often produced by high temperatures and are found in flames and explosions.



		The action of ultraviolet radiation from the sun splits chlorofluorocarbon (CFC) molecules in the upper atmosphere into free radicals, which then break down the ozone layer.



		A very simple free radical is the methyl radical CH₂ produced by the splitting of the covalent carbon-to-carbon bond in ethane.



		*compounds*



		The elements react with one another to form an enormous variety of different compounds. Some common classes of compound are illustrated below.



		*acids* Any compound that releases hydrogen ions (H⁺ or protons) in the presence of an ionizing solvent (usually water) is called an acid. Acids react with bases to form salts, and they act as solvents. Strong acids are corrosive; dilute acids have a sour or sharp taste, although in some organic acids this may be partially masked by other flavor characteristics. The strength of an acid is measured by its hydrogen-ion concentration, indicated by the pH value (see below). All acids have a pH below 7.0.



		Acids can be classified as monobasic, dibasic, tribasic, and so on, according to their basicity (the number of hydrogen atoms available to react with a base) and degree of ionization (how many of the available hydrogen atoms dissociate in water). Dilute sulfuric acid is classified as a strong (highly ionized), dibasic acid.



		Inorganic acids include boric, carbonic, hydrochloric, hydrofluoric, nitric, phosphoric, and sulfuric. Organic acids include acetic (vinegar), benzoic, citric, formic, lactic, oxalic, and salicylic, as well as complex substances such as nucleic acids and amino acids.



		Sulfuric, nitric, and hydrochloric acid are sometimes

Page 85



		referred to as the mineral acids. Most naturally occurring acids are found as organic compounds, such as the fatty acids R-COOH and sulfonic acids R-SOOH, where R is an organic group.



		All acids produce hydrogen ions when dissolved in water; for example hydrochloric acid is produced when hydrogen chloride gas dissolves in water.

acid



		To remember how to mix acid and water safely:



		Add acid to water, just as you oughter!



		The reactions of acids are the reactions of the H⁺ion. These are as follows.



		with indicators They give a specific color reaction with indicators; for example, litmus turns red.



		with alkalis They react with alkalis to form a salt and water (neutralization). For example, hydrochloric acid added to sodium hydroxide gives the salt sodium chloride plus water.



		Acids react with many bases, such as oxides and hydroxides, but the product is not always soluble in water so the reaction soon ceases, as when sulfuric acid reacts with calcium oxide, hydroxide, or carbonate.



		with carbonates With carbonates and hydrogencarbonates, acids form a salt and displace carbon dioxide. For example, as with nitric acid added to sodium hydrogencarbonate:



		with metals Acids react with metals to give off hydrogen and form a salt. For example, with magnesium and sulfuric acid the products are magnesium sulfate and hydrogen.



		pH scale from 0 to 14 for measuring acidity or alkalinity. A pH of 7.0 indicates neutrality, below 7 is acid, while above 7 is alkaline. Strong acids, such as those used in car batteries, have a pH of about 2; strong alkalis such as sodium hydroxide are pH 13.



		Acidic fruits such as citrus fruits are about pH 4. Fertile soils have a pH of about 6.5 to 7.0, while weak alkalis such as soap are 9 to 10.



		The pH of a solution can be measured by using a broad-range indicator, either in solution or as a paper strip. The color produced by the indicator is compared with a color code related to the pH value. An alternative method is to use a pH meter fitted with a glass electrode.

Sören Sörenson and pH
http://dbhs.wvusd.kl2.ca.us/Chem-History/Sorenson-article.html

Excerpt from a paper on enzymatic processes in which Sörenson defined pH as the relative concentration of hydrogen ions in a solution.



		*bases and alkalis* A base is the chemical opposite of an acid: it accepts protons. Bases can contain negative ions such as the hydroxide ion (OH^–), which is the strongest base, or be molecules such as ammonia (NH₃). Ammonia is a weak base, as only some of its molecules accept protons. Bases that dissolve in water are called alkalis.



		Inorganic bases are usually oxides or hydroxides of metals, which react with dilute acids to form a salt and water. Many carbonates also react with dilute acids, additionally giving off carbon dioxide.



		Alkalis neutralize acids and are soapy to the touch. The strength of an alkali is measured by its hydrogen-ion concentration, indicated by the pH value. They may be divided into strong and weak alkalis: a strong alkali (for example, potassium hydroxide, KOH) ionizes completely when dissolved in water, whereas a weak alkali (for example, ammonium hydroxide, NH₄OH) exists in a partially ionized state in solution. All alkalis have a pH above 7.0.



		The hydroxides of metals are alkalis. Those of sodium and potassium are chemically powerful; both were historically derived from the ashes of plants.



		The four main alkalis are sodium hydroxide (caustic soda, NaOH); potassium hydroxide (caustic potash, KOH); calcium hydroxide (slaked lime or limewater, Ca(OH)₂); and aqueous ammonia (NH₃(aq)). Their solutions all contain the hydroxide ion OH^–, which gives them a characteristic set of properties.



		with acids Alkalis react with acids to form a salt and water (neutralization). For example potassium hydroxide and nitric acid gives potassium nitrate and water:



		with indicators They give a specific color reaction with indicators; for example, litmus turns blue.

Page 86



		with ammonium salts Alkalis displace ammonia gas from ammonium salts:



		with soluble salts Alkalis precipitate the insoluble hydroxides of most metals from soluble salts. For example iron chloride:



		*salts* A salt is any compound formed from an acid and a base through the replacement of all or part of the hydrogen in the acid by a metal or electropositive radical. Common salt is sodium chloride.



		A salt may be produced by a chemical reaction between an acid and a base, or by the displacement of hydrogen from an acid by a metal (see displacement activity). As a solid, the ions normally adopt a regular arrangement to form crystals. Some salts only form stable crystals as hydrates (when combined with water). Most inorganic salts readily dissolve in water to give an electrolyte (a solution that conducts electricity).



		As all salts are electrically neutral, the formula of a salt can be worked out by making sure that the total numbers of positive and negative charges arising from the ions are equal.

Common Ions That Form Salts

hydrogencarbonate HCO₃_–

iron(II) Fe²⁺

hydrogensulfate HSO₄_–



		*preparation*



		Various methods can be used to prepare salts in the laboratory; the choice is dictated by the starting materials available and by whether the required salt is soluble or insoluble.



		Methods include:



		(i) acid + metal for salts of magnesium, iron, and zinc;



		(ii) acid + base for salts of magnesium, iron, zinc, and calcium;



		(iii) acid + carbonate for salts of all metals;



		(iv) acid + alkali for salts of sodium, potassium, and ammonium;



		(v) direct combination for sulfides and chlorides;



		(vi) double decomposition for insoluble salts.



		In methods (i)–(iii) an excess of the solid reactant is added to the acid to ensure that no acid remains. The excess solid is filtered from the salt solution and the filtrate is boiled to a much smaller volume; it is then allowed to cool and crystallize. The salt crystals are filtered and dried on filter paper.



		In method (iv) an indicator is used to determine the volume of acid needed to neutralize the alkali (or vice versa). The color can then be removed by charcoal treatment, or alternatively the experiment can be repeated without the indicator. The solution is boiled to a smaller volume, cooled to crystallize the salt, and the crystals filtered and dried as in (i)-(iii) above.



		In method (v) the salt is made in one step and does not require drying.



		In method (vi) the two solutions are mixed and stirred. The precipitated salt is filtered, washed well with water to remove the soluble impurities, and allowed to dry in air or an oven at 60–80°C/ 140–176°E

salts



		To create a salt:



		If a soluble salt you wish to provide, You first on the acid settle; Then neutralize with the proper oxide, hydroxide, carbonate, or metal But if the salt will not dissolve, A simpler means you'll try: Precipitate it, you resolve, Then filter, wash, and dry



		*oxides* Oxygen is a highly reactive element and combines with a variety of other elements to form oxides, frequently by burning the element or a compound of it in air.



		Oxides of metals are normally bases and will react with an acid to produce a salt in which the metal forms the cation. Some of them will also react with a strong

Page 87



		alkali to produce a salt in which the metal is part of a complex anion. Most oxides of nonmetals are acidic (dissolve in water to form an acid). Some oxides display no pronounced acidic or basic properties.

oxidation and reduction: principles



		To remember the principles of oxidation and reduction:



		Remember that Leo the lion goes ''ger"



		(Lose electrons-oxidation, gain electrons-reduction)



		oxidizing and reducing agents Oxidation is the loss of electrons, gain of oxygen, or loss of hydrogen by an atom, ion, or molecule during a chemical reaction. An oxidizing agent brings about oxidation by accepting electrons or hydrogen from a compound, or donating oxygen to that compound, and is simultaneously reduced in the reaction. Oxidation may also be brought about electrically at the anode (positive electrode) of an electrolytic cell.



		Reduction is the opposite of oxidation, that is the gain of electrons or hydrogen, or the loss of oxygen. Reduction of a compound may be brought about by reaction with a reducing agent, which is simultaneously oxidized, or electrically at the cathode (negative electrode) of an electric cell. Examples include the reduction of iron(III) oxide to iron by carbon monoxide:



		the hydrogenation of ethene to ethane:



		and the reduction of a sodium ion to sodium.



		A redox reaction is said to occur where one reactant is reduced and the other reactant oxidized. The reaction can only occur if both reactants are present and each changes simultaneously. For example, hydrogen reduces copper (II) oxide to copper while it is itself oxidized to water:

oxidation and reduction: electrons



		To remember the difference between oxidation and reduction with relation to electrons:



		OILRIG



		(Oxidation is loss; Reduction is gain)



		Physical Chemistry



		Most chemical reactions exhibit some physical phenomena (change of state, temperature, pressure, or volume, or the use or production of electricity or light). Physical chemistry is the branch of chemistry concerned with examining the relationships between the chemical compositions of substances and the physical properties that they display. The measurement and study of such phenomena has led to many chemical theories and laws.



		*physical states of matter*



		*gas* A gas is a form of matter, such as air, in which the molecules move randomly in otherwise empty space, filling any size or shape of container into which the gas is put.



		*liquid* A liquid is a state of matter between a solid and a gas. A liquid forms a level surface and assumes the shape of its container. Its atoms do not occupy fixed positions as in a crystalline solid, nor do they have freedom of movement as in a gas. Unlike a gas, a liquid is difficult to compress since pressure applied at one point is equally transmitted throughout (Pascal's principle). Hydraulics makes use of this property.



		*solid* A solid is a a state of matter that holds its own shape. According to kinetic theory, the atoms or molecules in a solid are not free to move but merely vibrate about fixed positions, such as those in crystal lattices.



		*solution* A solution is two or more substances mixed to form a single, homogenous phase. One of the substances is the solvent and the others (solutes) are said to be dissolved in it.



		The constituents of a solution may be solid, liquid, or gaseous. The solvent is normally the substance that is present in greatest quantity; however, if one of the constituents is a liquid this is considered to be the solvent even if it is not the major substance. Although the commonest solvent is water, in popular use the term refers to low-boiling-point organic liquids, which are harmful if used in a confined space. They can give rise to respiratory problems, liver damage, and neurological complaints.



		Typical organic solvents are petroleum distillates (in glues), xylene (in paints), alcohols (for synthetic and natural resins such as shellac), esters (in lacquers, including nail polish), ketones (in cellulose lacquers and resins), and chlorinated hydrocarbons (as paint stripper and dry-cleaning fluids). The fumes of some solvents, when inhaled (glue-sniffing), affect mood and

Page 88

Densities of Some Common Substances



		Substance



		Density in kg m^–3

Solids



		balsa wood



		200



		oak



		700



		butter



		900



		ice



		920



		ebony



		120



		sand (dry)



		1,600



		concrete



		2,400



		aluminum



		2,700



		aluminum



		2,700



		steel



		7,800



		copper



		8,900



		lead



		11,300



		uranium



		19,000

Liquids



		water



		1,000



		gasoline, paraffin



		800



		olive oil



		900



		milk



		1,030



		sea water



		1,030



		glycerin



		1,260



		Dead Sea brine



		1,800

Gases



		(at standard temperature and pressure of 0ºC and 1 atm)



		air



		1.30



		hydrogen



		0.09



		helium



		0.18



		methane



		0.72



		nitrogen



		1.25



		oxygen



		1.43



		carbon dioxide



		1.98



		propane



		2.02



		butane (iso)



		2.60



		perception. In addition to damaging the brain and lungs, repeated inhalation of solvent from a plastic bag can cause death by asphyxia.



		*suspension* A suspension is a mixture consisting of small solid particles dispersed in a liquid or gas, which will settle on standing. An example is milk of magnesia, which is a suspension of magnesium hydroxide in water.



		*colloid* A colloid is a substance composed of extremely small particles of one material (the dispersed phase) evenly and stably distributed in another material (the continuous phase). The size of the dispersed particles (1–1,000 nanometers across) is less than that of particles in suspension but greater than that of molecules in true solution. Colloids involving gases include aerosols (dispersions of liquid or solid particles in a gas, as in fog or smoke) and foams (dispersions of gases in liquids).



		Those involving liquids include emulsions (in which both the dispersed and the continuous phases are liquids) and sols (solid particles dispersed in a liquid). Sols in which both phases contribute to a molecular three-dimensional network have a jellylike form and are known as gels; gelatin, starch "solution," and silica gel are common examples.



		*gel* A gel is a solid produced by the formation of a three-dimensional cage structure, commonly of linked large-molecular-mass polymers, in which a liquid is trapped. It is a form of colloid. A gel may be a jellylike mass (pectin, gelatin) or have a more rigid structure (silica gel).



		*kinetic theory of matter*



		According to the molecular or kinetic theory of matter, matter is made up of molecules that are in a state of constant motion, the extent of which depends on their temperature. Molecules also exert forces on one another. The nature and strength of these forces depends on the temperature and state of the matter (solid, liquid, or gas).



		The existence of molecules was first inferred from the Italian physicist Amedeo Avogadro's hypothesis in 1811. He observed that when gases combine, they do so in simple proportions. For example, exactly one volume of oxygen and two volumes of hydrogen combine to produce water. He hypothesized that equal volumes of gases at the same temperature and pressure contain equal numbers of molecules. Avogadro's hypothesis only became generally accepted in 1860, when proposed by the Italian chemist Stanislao Cannizzaro.

Avogadro's Hypothesis of 1811
http://dbhs.wvusd.k12.ca.us/Chem-History/Avogadro.htm1

Transcript of a translation of the essay containing Avogadro's hypothesis.

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		The movement of some molecules can be observed in a microscope. As early as 1827, Robert Brown observed that very fine pollen grains suspended in water move about in a continuously agitated manner. This continuous, random motion of particles in a fluid medium (gas or liquid) as they are subjected to impact from the molecules of the medium is known as Brownian movement.



		The spontaneous and random movement of molecules or particles in a fluid can also be observed as diffusion occurs from a region in which they are at a high concentration to a region of lower concentration, until a uniform concentration is achieved throughout. No mechanical mixing or stirring is involved. For example, if a drop of ink is added to water, its molecules will diffuse until the color becomes evenly distributed.



		In biological systems, diffusion plays an essential role in the transport, over short distances, of molecules such as nutrients, respiratory gases, and neurotransmitters. It provides the means by which small molecules pass into and out of individual cells and microorganisms, such as amoebas, that possess no circulatory system. Plant and animal organs whose function depends on diffusion—such as the lung—have a large surface area. Diffusion of water across a semipermeable membrane is termed osmosis.



		diffusion Diffusion is the movement of molecules from a region of high concentration into a region of lower concentration.



		One application of diffusion is the separation of isotopes, particularly those of uranium. When uranium hexafluoride diffuses through a porous plate, the ratio of the 235 and 238 isotopes is changed slightly. With sufficient number of passages, the separation is nearly complete. There are large plants in the United States and U.K. for obtaining enriched fuel for fast nuclear reactors and the fissile uranium–235, originally required for the first atomic bombs. Another application is the diffusion pump, used extensively in vacuum work, in which the gas to be evacuated diffuses into a chamber from which it is carried away by the vapor of a suitable medium, usually oil or mercury.



		Laws of diffusion were formulated by Thomas Graham in 1829 (for gases) and Adolph Fick 1829–1901 (for solutions).



		*kinetic theory of gases*



		The effects of pressure, temperature, and volume on a gas were investigated during the 17th and 18th centuries. Boyle's law states that for a fixed mass of gas the volume of the gas is inversely proportional to the pressure at constant temperature. Charles's law states that for a fixed mass of gas the volume of the gas is proportional to the absolute temperature at constant pressure. The pressure law states that the pressure of a fixed mass of gas at constant volume is directly proportional to its absolute temperature.



		These statements together give the gas laws which can be expressed as: A plot of the volume of a gas against its temperature gives a straight line, showing that the two are proportional. The line intercepts the x axis at –273°C/–459°F. This suggests that, if the gas did not liquefy first, it would occupy zero volume at a temperature of –273°C/–459ºF. This temperature is referred to as absolute zero, or zero Kelvin (0K) on the Kelvin scale, and is the lowest temperature theoretically possible.



		This behavior applies only to ideal gases, which are assumed to occupy negligible volume and contain negligible forces between particles. A real gas often behaves rather differently, and the van der Waals' law contains a correction to the gas laws to account for the nonideal behavior of real gases.



		*change of state*



		As matter is heated its temperature may rise or it may cause a change of state. As the internal energy of matter increases the energy possessed by each particle

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		increases too. This can be visualized as the kinetic energy of the molecules increasing, causing them to move more quickly. This movement includes both vibration within the molecule (assuming the substance is made of more than one atom) and rotation.



		A solid is made of particles that are held together by forces. As a solid is heated, the particles vibrate more vigorously, taking up more space, and causing the material to expand. As the temperature of the solid increases, it reaches its melting point and turns into a liquid. The particles in a liquid can move around more freely but there are still forces between them. As further energy is added, the particles move faster until they are able to overcome the forces between them. When the boiling point is reached the liquid boils and becomes a gas. Gas particles move around independently of one another except when they collide.



		Different objects require different amounts of heat energy to change their temperatures by the same amount. The heat capacity of an object is the quantity of heat required to raise its temperature by one degree. The specific heat capacity of a substance is the heat capacity per unit of mass, measured in joules per kilogram per kelvin. As a substance is changing state while being heated, its temperature remains constant, provided that thermal energy is being added. For example, water boils at a constant temperature as it turns to steam. The energy required to cause the change of state is called latent heat. This energy is used to break down the forces holding the particles together so that the change in state can occur. Specific latent heat is the thermal energy required to change the state of a certain mass of that substance without any temperature change. Evaporation causes cooling as a liquid vaporizes.



		Heat is transferred by the movement of particles (that possess kinetic energy) by conduction, convection, and radiation. Conduction involves the movement of heat through a solid material by the movement of free electrons. Convection involves the transfer of energy by the movement of fluid particles. Convection currents are caused by the expansion of a liquid or gas as its temperature rises. The expanded material, being less dense, rises above colder and therefore denser material.



		*attraction and repulsion*



		Atoms are held together by the electrical forces of attraction between each negative electron and the positive protons within the nucleus. The latter repel one another with enormous forces; a nucleus holds together only because an even stronger force, called the strong nuclear force, attracts the protons and neutrons to one another. The strong force acts over a very short range—the protons and neutrons must be in virtual contact with one another. If, therefore, a fragment of a complex nucleus, containing some protons, becomes only slightly loosened from the main group of neutrons and protons, the natural repulsion between the protons will cause this fragment to fly apart from the rest of the nucleus at high speed. It is by such fragmentation of atomic nuclei (nuclear fission) that nuclear energy is released.



		*two Greek theories* Among the ancient Greeks there were two theories as to the nature of matter, or substance. Some, such as Anaxagoras and Aristotle, held that matter was infinite and continuous, and that therefore any substance could theoretically be divided and subdivided to an infinite extent. Others, such as Democritus and Epicurus, taught that matter was grained, that is, consisted of minute particles which could not be divided. Both theories were based on naturally slender experimental evidence.



		*the conservation of matter* Towards the end of the 18th century, the development of experimental chemistry demanded greater quantitative exactness, and experimental evidence, primarily from studies in combustion, led to the principle of the conservation of matter. The value of this principle has been enormous, particularly in the direction of detecting new elements.



		*Dalton's theory* John Dalton, in the 19th century, believed that gases consisted of particles or "corpuscles." He appears to have reasoned that, as all the particles of the same substances are alike, any chemical action between two substances means a corresponding change in the individual particles of the substances concerned. Particles of a compound must therefore be divisible into atomic particles of the atoms combined. Dalton enunciated the law of constant proportions, which states that when two elements unite to form a compound they do so in a constant ratio that is characteristic of that compound. For instance, when oxygen and hydrogen combine to form water, the weights combining always take the same ratio.



		*determining atomic weights* Shortly after Dalton's atomic theory had been enunciated, Joseph Gay-Lussac investigated the volumetric conditions of gases in combination, with the result that he discovered and published the law that when gases combine together they do so in volumes which bear a simple ratio to one another and to that of their product (if gaseous). In 1811 Amadeo Avogadro published his hypothesis on the molecular constitution of gases, which asserts that

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		under the same conditions of temperature and pressure equal volumes of all gases contain the same number of molecules whether those molecules consist of single atoms or many atoms in combination. Both hypotheses were well supported by experimental evidence, and were used to determine the atomic weights of the elements. Much of the progress in chemistry has been based on quantitative analysis using atomic weights.



		*Rutherford and Moseley* Around 1900 it became apparent that atoms themselves have structure and are not indivisible. From his experiments with alpha particles, Ernest Rutherford and others (1911–13) showed that practically the whole mass of any atom is concentrated in an extremely small central nucleus bearing a positive electrical charge. With Henry Moseley in 1913 he showed that the nucleus contains a number of positive charges dependent on the element, and called the atomic number of the element. Around the nucleus move an equal number of electrons at a relatively great distance. The lightest nucleus, the hydrogen nucleus, contains a single positive charge, and is called a proton.



		*Bohr* In 1913 Niels Bohr proposed that the electrons move in orbits around the nucleus like planets round the sun, and suggested how atoms might emit or absorb light. These ideas were developed and applied with great success by Bohr and others using quantum theory, to the full elucidation of atomic structure, and the explanation of the properties of matter in bulk, and of the substructure of the nucleus itself.



		*Chadwick* In 1932 James Chadwick discovered that the bombardment of beryllium by alpha particles produced neutral particles which he called neutrons. From the atomic weights of atoms, and the known weights of the proton and the electron it became clear that (1) protons and neutrons have essentially equal masses, and (2) that atomic nuclei contain approximately equal numbers of protons and neutrons, the protons carrying the nuclear charge.



		*subatomic particles* High-energy physics research has discovered the existence of subatomic particles other than the proton, neutron, and electron. More than three hundred kinds of particle are now known, and these are classified into several classes according to their mass, electric charge, spin, magnetic moment, and interaction. The elementary particles, which include the electron, are indivisible and may be regarded as the fundamental units of matter; the hadrons, such as the proton and neutron, are composite particles made up of either two or three elementary particles called quarks.



		*electronic structure of the atom*



		Electrons are arranged around the nucleus of an atom in distinct energy levels, also called orbitals or shells. These shells can be regarded as a series of concentric spheres, each of which can contain a certain maximum number of electrons; the noble gases have an arrangement in which every shell contains this number. The energy levels are usually numbered beginning with the shell nearest to the nucleus. The outermost shell is known as the valence shell as it contains the valence electrons.



		The lowest energy level, or innermost shell, can contain no more than two electrons. Outer shells are considered to be stable when they contain eight electrons but additional electrons can sometimes be accommodated provided that the outermost shell has a stable configuration. Electrons in unfilled shells are available to take part in chemical bonding, giving rise to the concept of valency. In ions, the electron shells contain more or fewer electrons than are required for a neutral atom, generating negative or positive charges.



		The atomic number of an element indicates the number of electrons in a neutral atom. From this it is possible to deduce its electronic structure. For example,



		orbital The shapes of atomic orbitals. An atomic orbital is a picture of the "electron cloud" that surrounds the nucleus of an atom. There are four basic shapes for atomic orbitals: spherical, dumbbell, cloverleaf, and complex (shown at bottom left).



		sodium has atomic number 11 (Z = 11) and its electronic arrangement (configuration) is two electrons in the first energy level, eight electrons in the second energy level and one electron in the third energy level—generally written as 2.8.1. Similarly for sulfur (Z = 16), the electron arrangement will be 2.8.6. The electronic structure dictates whether two elements will combine by ionic or covalent bonding or not at all.



		*chemical reactions* Physical chemistry is interested in the mechanics of how chemical change takes place. Chemical equations show the reactants and products of a chemical reaction by using chemical symbols and formulas.



		State symbols and the energy symbol (DH) can be used to show whether reactants and products are solids, liquids, or gases, and whether energy has been released or absorbed during the reaction. Elements, compounds, and ions may react with each other in many different ways.



		addition reactions: two or more compounds react together to form one compound. For example hydrogen chloride reacts with ethene to give chloroethane:



		chain reactions produce very fast, exothermic reactions, as in the formation of flames and explosions.



		displacement reactions: a less reactive element is replaced in a compound by a more reactive one. For example, the addition of powdered zinc to a solution of copper (II) sulfate displaces copper metal, which can be detected by its characteristic color.



		endothermic reactions: there is a physical or chemical change where energy is absorbed by the reactants from the surroundings. The energy absorbed is represented by the symbol +DH. Photosynthesis is an example.



		exothermic reactions: chemical reactions during which heat is given out. (DH is negative)



		heterogeneous reactions: there is an interface between the different components or reactants. Examples of heterogeneous reactions are those between a gas and a solid or between two immiscible liquids.



		homogeneous reactions: there is no interface between the components. The term applies to all reactions where only gases are involved or where all the components are in solution.



		photochemical reactions: light is produced or light initiates the reaction. Light can initiate reactions by exciting atoms or molecules and making them more reactive: the light energy becomes converted to chemical energy.



		redox reactions: one reactant is reduced and the other reactant oxidized. The reaction can only occur if both reactants are present and each changes simultaneously. For example, hydrogen reduces copper (II) oxide to copper while it is itself oxidized to water:



		reversible reactions: proceed in both directions at the same time, as the product decomposes back into reactants as it is being produced. Such reactions do not run to completion, provided that no substance leaves the system. The manufacture of ammonia from hydrogen and nitrogen is an example:



		The term is also applied to those reactions that can be made to go in the opposite direction by changing the conditions, but these run to completion because some of the substances escape from the reaction. An example is the decomposition of calcium hydrogencarbonate on heating:



		substitution reactions: one atom or functional group in an organic molecule is replaced by another.



		*catalysts* A catalyst is a substance that alters the speed of, or makes possible, a chemical or biochemical reaction but remains unchanged at the end of the reaction. Enzymes are natural biochemical catalysts. In practice most catalysts are used to speed up reactions.



		*electrolysis*



		If an electric current is passed through a solution or molten salt (the electrolyte), ions will migrate to the electrodes: positive ions (cations) to the negative

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		electrode (cathode) and negative ions (anions) to the positive electrode (anode).



		During electrolysis, the ions react with the electrode, either receiving or giving up electrons (see oxidation and reduction). The resultant atoms may be liberated as a gas, or deposited as a solid on the electrode, in amounts that are proportional to the amount of current passed, as discovered by English chemist Michael Faraday. For instance, when acidified water is electrolyzed, hydrogen ions (H⁺) at the cathode receive electrons to form hydrogen gas; hydroxide ions (OH^–) at the anode give up electrons to form oxygen gas and water.



		One application of electrolysis is electroplating, in

The Transuranic Elements



		A transuranic element is a chemical element with an atomic number of 93 or more—that is, with a greater number of protons in the nucleus than uranium. All transuranic elements are radioactive. (– = not applicable.)



		Atomic number

Name

Symbol

Year discovered

Source of first
preparation identified

Isotope

Half-life of first isotope identified

Actinide Series



		93

neptunium

1940

irradiation of uranium–238 with neutrons

Np–239

2.35 days



		94

plutonium

1941

bombardment of uranium–238 with deuterons

Pu–238

86.4 years



		95

americium

1944

irradiation of plutonium–239 with neutrons

Am–241

458 years



		96

curium

1944

bombardment of plutonium–239 with helium nuclei

Cm–242

162.5 days



		97

berkelium

1949

bombardment of americium–241 with helium nuclei

Bk–243

4.5 h



		98

californium

1950

bombardment of curium–242 with helium nuclei

Cf–245

44 min



		99

einsteinium

1952

irradiation of uranium–238 with neutrons in first thermonuclear explosion

Es–253

20 days



		100

fermium

1953

irradiation of uranium–238 with neutrons in first thermonuclear explosion

Fm–235

20 h



		101

mendelevium

1955

bombardment of einsteinium–253 with helium nuclei

Md–256

76 min



		102

nobelium

1958

bombardment of curium–246 with carbon nuclei

No–255

2.3 sec



		103

lawrencium

1961

bombardment of californium–252 with boron nuclei

Lr–257

4.3 sec

Transactinide Elements



		104

rutherfordium

1969

bombardment of californium–249 with carbon–12 nuclei

Db–257

3.4 sec



		105

dubnium

1970

bombardment of californium–249 with nitrogen–15 nuclei

Unp–260

1.6 sec



		106

seaborgium

1974

bombardment of californium–249 with oxygen–18 nuclei

Rf–263

0.9 sec



		107

bohrium

1977

bombardment of bismuth–209 with nuclei of chromium–54

Uns

102 millisec



		108

hassium

1984

bombardment of lead–208 with nuclei of iron–58

Uno–265

1.8 millisec



		109

meitnerium

1982

bombardment of bismuth–209 with nuclei of iron–58

Une

3.4 millisec



		110

ununnilium¹

Uun

1994

bombardment of lead nuclei with nickel nuclei

–



		111

unununium¹

Uuu

1994

bombardment of bismuth–209 with nickel nuclei

–



		¹ Temporary names as proposed by the International Union for Pure and Applied Chemistry.

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		which a solution of a salt, such as silver nitrate (AgNO₃), is used and the object to be plated acts as the negative electrode, thus attracting silver ions (Ag⁺). Electrolysis is used in many industrial processes, such as coating metals for vehicles and ships, and refining bauxite into aluminum; it also forms the basis of a number of electrochemical analytical techniques, such as polarography.



		*radioactivity*



		The nuclei of many large atoms may disintegrate spontaneously, emitting energy as alpha particles (helium nuclei), beta particles (electrons), or gamma radiation. Many of the elements with high atomic numbers exist as mixtures of isotopes, atoms that have the same number of protons in the nucleus but different numbers of neutrons. The average time required for the radioactivity of a sample to drop to half of its original value is known as the half-life and is a measure of the stability of that isotope.



		Elements with atomic numbers 43, 61, and from 84 up, are radioactive. Those elements with atomic numbers above 96 do not occur in nature and are synthesized only, produced in particle accelerators. Elements 110 and 111 were discovered in 1994 and 1995. Element 110 was detected for a millisecond at the GSI heavy-ion cyclotron in Darmstadt, Germany, while lead atoms were bombarded with nickel atoms. It has an atomic mass of 269. Element 111 was later detected at GSI, when bismuth-209 was bombarded with nickel. It has an atomic mass of 272. Element 112 was discovered there in 1996. It has an atomic mass of 277. After firing 5 billion billion zinc ions at a speed of 30,000 kps/18,640 mps at lead, the German scientists created a single atom of 112 that survived for a third of a millisecond.



		*uranium* Uranium is a hard, lustrous, silver-white, malleable and ductile, radioactive, metallic element of the actinide series, symbol U, with atomic number 92 and atomic weight 238.029. It is the most abundant radioactive element in the earth's crust, its decay giving rise to essentially all radioactive elements in nature; its final decay product is the stable element lead. Uranium combines readily with most elements to form compounds that are extremely poisonous. The chief ore is pitchblende, in which the element was discovered by German chemist Martin Klaproth in 1789; he named it after the planet Uranus, which had been discovered in 1781.



		Small amounts of certain compounds containing uranium have been used in the ceramics industry to make orange-yellow glazes and as mordants in dyeing; however, this practice was discontinued when the dangerous effects of radiation became known.



		Uranium is one of three fissile elements (i.e. it will undergo nuclear fission; the others are thorium and plutonium). It was long considered to be the element with the highest atomic number to occur in nature. The isotopes U-238 and U-235 have been used to help determine the age of the earth.



		Uranium-238, which comprises about 99% of all naturally occurring uranium, has a half-life of 4.51 x 10⁹ years. Because of its abundance, it is the isotope from which fissile plutonium is produced in breeder nuclear reactors. The fissile isotope U-235 has a half-life of 7.13 x 10⁸ years and comprises about 0.7% of naturally occurring uranium; it is used directly as a fuel for nuclear reactors and in the manufacture of nuclear weapons.



		Many countries mine uranium; large deposits are found in Canada, the United States, Australia, and South Africa.

What is Uranium?
http://www.uic.com.au/uran.htm

Comprehensive and informative page on uranium, its properties and uses, mainly in nuclear reactors and weapons, provided by the Uranium Information Council.



		Analytical Chemistry



		Analytical chemistry is the branch of chemistry that deals with the determination of the chemical composition of substances. Qualitative analysis determines the identities of the substances in a given sample; quantitative analysis determines how much of a particular substance is present.



		Simple qualitative techniques exploit the specific, easily observable properties of elements or compounds—for example, the flame test makes use of the different flame colors produced by metal cations when their compounds are held in a hot flame. More sophisticated methods, such as those of spectroscopy, are required where substances are present in very low concentrations or where several substances have similar properties.



		Most quantitative analyses involve initial stages in which the substance to be measured is extracted from the test sample, and purified. The final analytical stages (or "finishes") may involve measurement of the substance's mass (gravimetry) or volume (volumetry, titrimetry), or a number of techniques initially developed for qualitative analysis, such as fluorescence and absorption spectroscopy, chromatography, electrophoresis, and polarography. Many modern methods enable quantification by means of a detecting device that is integrated into the extraction procedure (as in gas—liquid chromatography).

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Analytical Chemistry Basics
http://www.scimedia.com/chem-ed/analytic/ac-basic.htm

Detailed online course, designed for those at undergraduate level, that provides the user with an introduction to some of the fundamental concepts and methods of analytical chemistry.



		*spectroscopy*



		Spectroscopy is the study of spectra associated with atoms or molecules in solid, liquid, or gaseous phase. Spectroscopy can be used to identify unknown compounds and is an invaluable tool in science, medicine, and industry (for example, in checking the purity of drugs).



		Emission spectroscopy is the study of the characteristic series of sharp lines in the spectrum produced when an element is heated. Thus an unknown mixture can be analyzed for its component elements. Related is absorption spectroscopy, dealing with atoms and molecules as they absorb energy in a characteristic way. Again, dark lines can be used for analysis. More detailed structural information can be obtained using infrared spectroscopy (concerned with molecular vibrations) or nuclear magnetic resonance (NMR) spectroscopy (concerned with interactions between adjacent atomic nuclei). Supersonic jet laser beam spectroscopy enables the isolation and study of clusters in the gas phase. A laser vaporizes a small sample, which is cooled in helium, and ejected into an evacuated chamber. The jet of clusters expands supersonically, cooling the clusters to near absolute zero, and stabilizing them for study in a mass spectrometer.



		*chromatography*



		Chromatography (from the Greek chromos "color") is a technique for separating or analyzing a mixture of gases, liquids, or dissolved substances. This is brought about by means of two immiscible substances, one of which (the mobile phase) transports the sample mixture through the other (the stationary phase). The mobile phase may be a gas or a liquid; the stationary phase may be a liquid or a solid, and may be in a column, on paper, or in a thin layer on a glass or plastic support. The components of the mixture are absorbed or impeded by the stationary phase to different extents and therefore become separated. The technique is used for both qualitative and quantitive analyses in biology and chemistry.



		In paper chromatography, the mixture separates because the components have differing solubilities in the solvent flowing through the paper and in the chemically bound water of the paper.



		In thin-layer chromatography, a wafer-thin layer of adsorbent medium on a glass plate replaces the filter paper. The mixture separates because of the differing solubilities of the components in the solvent flowing up the solid layer, and their differing tendencies to stick to the solid (adsorption). The same principles apply in column chromatography.



		In gas-liquid chromatography, a gaseous mixture is passed into a long, coiled tube (enclosed in an oven) filled with an inert powder coated in a liquid. A carrier gas flows through the tube. As the mixture proceeds along the tube it separates as the components dissolve in the liquid to differing extents or stay as a gas. A detector locates the different components as they emerge from the tube. The technique is very powerful, allowing tiny quantities of substances (fractions of parts per million) to be separated and analyzed.



		Preparative chromatography is carried out on a large scale for the purification and collection of one or more of a mixture's constituents; for example, in the recovery of protein from slaughterhouse wastes.



		Analytical chromatography is carried out on far smaller quantities, often as little as one microgram (one-millionth of a gram), in order to identify and quantify the component parts of a mixture. It is used to determine the identities and amounts of amino acids in a protein, and the alcohol content of blood and urine samples. The technique was first used in the separation of colored mixtures into their component pigments.

Chromatography
http://www.eng.rpi.edu/dept/chem-eng/Biotech-Environ/CHROMO/chromintro.html

Explanation of the theory and practice of chromatography. Designed for school students (and introduced by a Biotech Bunny), the contents include equipment, analyzing a chromatogram, and details of the various kinds of chromatography.



		*crystallography*



		Crystallography is the scientific study of crystals. In 1912 it was found that the shape and size of the repeating atomic patterns (unit cells) in a crystal could be determined by passing X-rays through a sample. This method, known as X-ray diffraction, opened up an entirely new way of "seeing" atoms. It has been found that many substances have a unit cell that exhibits all the symmetry of the whole crystal; in table salt (sodium chloride, NaCI), for instance, the unit cell is an exact cube.



		Applications of Chemistry



		There can be few aspects of the modern world that have remained unaffected by the discoveries of chemists

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		and the industrial and commercial application of these discoveries. Medical practice has been revolutionized in the past century by the development of modern pharmaceutical drugs, allowing effective treatment of an ever wider set of ailments. The petrochemical industry has come up with countless new materials with properties suited to specialized applications, as well as fertilizers and pesticides that have radically changed the way that food is produced, preserved, and presented. The ability to produce highly complex electrical circuitry on silicon chips, and the development of miniature electrical power sources have led to the computer revolution that has had a huge impact on many aspects of design, production, finance, and entertainment.



		A few applications of chemistry are outlined below.



		*the battery*



		An electrical battery or electrical cell is a device in which chemical energy is converted into electrical energy (the popular name "battery" actually refers to a collection of cells in one unit). The reactive chemicals of a primary cell cannot be replenished, whereas secondary cells—such as storage batteries—are rechargeable: their chemical reactions can be reversed and the original condition restored by applying an electric current. Primary-cell batteries are an extremely uneconomical form of energy, since they produce only 2% of the power used in their manufacture. It is dangerous to attempt to recharge a primary cell.



		Each cell contains two conducting electrodes immersed in an electrolyte, in a container. A spontaneous chemical reaction within the cell generates a negative charge (excess of electrons) on one electrode, and a positive charge (deficiency of electrons) on the other. The accumulation of these equal but opposite charges prevents the reaction from continuing unless an outer connection (external circuit) is made between the electrodes allowing the charges to dissipate.



		When this occurs, electrons escape from the cell's negative terminal and are replaced at the positive, causing a current to flow. After prolonged use, the cell will become flat (ceases to supply current). The first cell was made by Italian physicist Alessandro Volta in 1800. Types of primary cells include the Daniell, Lalande, Leclanché, and so-called "dry" cells; secondary cells include the Planté, Faure, and Edison. Newer types include the Mallory (mercury depolarizer), which has a very stable discharge curve and can be made in very small units (for example, for hearing aids), and the Venner accumulator, which can be made substantially solid for some purposes. Rechargeable nickel-cadmium dry cells are available for household use.



		cell, electrical When electrical energy is produced from chemical energy using two metals acting as electrodes in an aqueous solution, it is sometimes known as a galvanic cell or voltaic cell. Here the two metals copper (+) and zinc (–) are immersed in dilute sulfuric acid, which acts as an electrolyte. If a light bulb is connected between the two, an electric current will flow with bubbles of gas being deposited on the electrodes in a process known as polarization.



		The reactions that take place in a simple cell depend on the fact that some metals are more reactive than others. If two different metals are joined by an electrolyte and a wire, the more reactive metal loses electrons to form ions. The ions pass into solution in the electrolyte, while the electrons flow down the wire to the less reactive metal. At the less reactive metal the electrons are taken up by the positive ions in the electrolyte, which completes the circuit. If the two metals are zinc and copper and the electrolyte is dilute sulfuric acid, the following cell reactions occur. The zinc atoms dissolve as they lose electrons (oxidation):



		The two electrons travel down the wire and are taken up by the hydrogen ions in the electrolyte (reduction):

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		The overall cell reaction is obtained by combining these two reactions; the zinc rod slowly dissolves and bubbles of hydrogen appear at the copper rod:



		If each rod is immersed in an electrolyte containing ions of that metal, and the two electrolytes are joined by a salt bridge, metallic copper deposits on the copper rod as the zinc rod dissolves in a redox reaction, just as if zinc had been added to a copper salt-solution:



		*adhesives*



		Natural adhesives (glues) include gelatin in its crude industrial form (made from bones, hide fragments, and fish offal) and vegetable gums. Synthetic adhesives include thermoplastic and thermosetting resins, which are often stronger than the substances they join; mixtures of epoxy resin and hardener that set by chemical reaction; and elastomeric (stretching) adhesives for flexible joints. Superglues are fast-setting adhesives used in very small quantities.



		*natural water-based adhesives* Typical natural substances used for water-based adhesives are starch, casein, tree exudates, skin, and bones.



		Starch, usually provided from corn, potato, tapioca, or sago, is extracted from the vegetable matter by disintegration and extraction with cold water. Dextrin is prepared from starch by roasting it in the presence of acid or by acid hydrolysis. Its adhesive properties vary widely with the source of the starch and the degree of hydrolysis.



		Casein is prepared from milk by precipitating its protein with acid or rennet. After further purification the casein is dissolved in a solution of alkali or urea to form a strong adhesive.



		Among tree exudates, natural rubber latex is obtained from incisions in the bark of Hevea brasiliensis. Gum arabic (acacia) and gum tragacanth are solid exudates from Acacia leguminosae and Astragalus leguminosae respectively. These natural substances (except latex) are brittle when dry and support mold growth when wet. Adhesives are formulated from them by the additions of water, plasticizers, fungicides, tack, and wetting agents. Their adhesive action is due to the formation of physicochemical bonds and penetration to give mechanized keying. Setting and hardening of this type of adhesive depends on loss of water; therefore they are mainly used for joining porous substrates such as paper, board, and wood. As a group these natural adhesives are less waterproof and strong, but cheaper than the synthetic resin-based adhesives.



		*natural nonwater-based adhesives Bitumen,* derived from asphalt; shellac, produced by parasitic tree insects; and resin, an exudate from pine trees, are examples of naturally occurring resins used both as hot melt adhesives and as spirit-based cements.



		The marine bacterium Shewanell colwellü secretes a natural glue, PAVE (polysaccharide adhesive viscous exopolymer), in large quantities. Because PAVE can be used in wet conditions and is resistant to sea water, it has been developed commercially since 1994 as a sealant for ships' hulls.



		*synthetic adhesives* Many modern adhesives are based on the increasing number of synthetic resins available. Thanks to the chemists' closer control over these polymers, a wider variety of type and nomenclature of adhesives has evolved. Definitions, common uses, and the names of some resins used in these adhesives are listed below.



		Solution adhesives are resins dissolved in a volatile organic solvent, used for bonding porous materials. They include natural and synthetic rubbers, nitrocellulose, polyvinylacetate, and polymethylmethacrylate.



		Emulsion adhesives are resins dispersed in an aqueous base, used for bonding porous materials. Natural and synthetic rubbers, polyvinylacetate, and polymethylmethacrylate are used.



		Contact adhesives are emulsions or solutions formulated to bond impervious materials. Both faces are covered with adhesive and allowed to dry before being brought into contact. They are used for bonding plastics, sticking rubber shoe soles, and on self-seal envelopes.



		Pressure-sensitive adhesives are used on tapes or sheet material, sometimes with a nonstick backing paper. Applied pressure forms a bond. Some adhesives are formulated for ease and cleanliness of removal (permanently tacky adhesive), and some to give a permanent bond. The materials used include modified natural and synthetic rubbers and polyisobutylene.



		Thermoplastic adhesives are solventless adhesives, softened by the application of heat before bonding. They may be remelted after bonding and are used for high-speed packaging, labeling, and unsewn bookbinding. Polyamides and polyvinylacetate and its copolymers are used.



		Thermosetting adhesives are solventless, and are cured by heat to form a bond that, once cured, can

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		not be resoftened by heat. They are used for exterior plywood and for bonding brake linings to shoes. They are usually made from epoxy resins.



		Two-part or chemical-cure adhesives consist of resin and hardener, which are mixed together shortly before use and set by chemical action without the necessity for the application of heat. They are used for bonding aluminum alloys in the aircraft industry and varied domestic applications. Resins used include epoxypolyamide and resorcinol.



		Structural adhesives are adhesives of high strength, toughness, and creep resistance, used for bonding load-bearing members. They are mainly confined to chemical-cure and thermosetting adhesives.



		*plastics*



		Plastics are stable synthetic materials that are fluid at some stage in their manufacture, when they can be shaped, and that later set to rigid or semirigid solids. Plastics today are chiefly derived from petroleum. Most are polymers, made up of long chains of identical molecules.



		*environmental influence* Since plastics have afforded an economical replacement for ivory in the manufacture of piano keys and billiard balls, the industrial chemist may well have been responsible for the survival of the elephant.



		Most plastics cannot be broken down by microorganisms, so cannot easily be disposed of. Incineration leads to the release of toxic fumes, unless carried out at very high temperatures.



		Processed by extrusion, injection-molding, vacuum-forming, and compression, plastics emerge in consistencies ranging from hard and inflexible to soft and rubbery. They replace an increasing number of natural substances, being lightweight, easy to clean, durable, and capable of being rendered very strong—for example, by the addition of carbon fibers—for building aircraft and other engineering projects.



		*thermoplastics* Thermoplastics soften when warmed, then reharden as they cool. Examples of thermoplastics include polystyrene, a clear plastic used in kitchen utensils or (when expanded into a ''foam" by gas injection) in insulation and ceiling tiles; polyethylene, used for containers and wrapping; and polyvinyl chloride (PVC), used for drainpipes, floor tiles, audio discs, shoes, and handbags.



		*thermosets*



		Thermosets remain rigid once set, and do not soften when warmed. They include Bakelite, used in electrical insulation and telephone receivers; epoxy resins, used in paints and varnishes, to laminate wood, and as adhesives; polyesters, used in synthetic textile fibers and, with fiberglass reinforcement, in car bodies and boat hulls; and polyurethane, prepared in liquid form as a paint or varnish, and in foam form for upholstery and in lining materials (where it may be a fire hazard). One group of plastics, the silicones, are chemically inert, have good electrical properties, and repel water. Silicones find use in silicone rubber, paints, electrical insulation materials, laminates, waterproofing for walls, stain-resistant textiles, and cosmetics.



		*polyamides* Polyamides are widely used for the production of film, sheet, and injection-molded articles. Nylon, the first polyamide, was synthesized in 1934 by Wallace Carothers at the du Pont laboratories in the United States and was intended to have many of the properties possessed of natural silk. Although it does have other applications, nylon is known principally for its applications in the textile field. Nylon yarn, once it has been stretched during the filament-forming process, has a combination of properties unique among textile fibers. One of the most notable is remarkable tensile strength, combined with lightness in weight and a high degree of resilience.



		*shape-memory polymers* Shape-memory polymers are plastics that can be crumpled or flattened and will resume their original shape when heated. They include trans-polyisoprene and polynorbornene. The initial shape is determined by heating the polymer to over 35°C/95°F and pouring it into a metal mold. The shape can be altered with boiling water and the substance solidifies again when its temperature falls below 35°C/95°F.



		*biodegradable plastics* Biodegradable plastics are increasingly in demand: Biopol was developed in 1990. Soil microorganisms are used to build the plastic in their cells from carbon dioxide and water (it constitutes 80% of their cell tissue). The unused parts of the microorganism are dissolved away by heating in water. The discarded plastic can be placed in landfill sites where it breaks back down into carbon dioxide and water. It costs three to five times as much as ordinary plastics to produce. Another plastic digested by soil microorganisms is polyhydroxybutyrate (PHB), which is made from sugar.



		*celluloid* Celluloid is a transparent or translucent, highly flammable, plastic material (a thermoplastic) made from cellulose nitrate and camphor. It was once used for toilet articles, novelties, and photographic film, but has now been replaced by the nonflammable substance cellulose acetate.



		*intelligent gels* Intelligent gels are polymer gels that respond "intelligently" to their environments. Most gels shrink or swell in fairly strict proportion to the quality

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		of solvent added to them, but some undergo a sudden change in dimension in response to relatively small fluctuations. This rapid response could make gels suitable for use as "muscle" for robots, or as valves in engineering. They are also likely to have medical applications; for example, in long-term drug administration. The gel could sense conditions inside the body and vary drug delivery rate to maintain suitable levels in the bloodstream.



		*anodizing*



		The natural resistance to corrosion of a metal, such as aluminum, may be increased by building up a protective oxide layer on the surface. Anodizing increases the thickness of this film and thus the corrosion protection.



		It is so called because the metal becomes the anode in an electrolytic bath containing a solution of, for example, sulfuric or chromic acid as the electrolyte. During electrolysis oxygen is produced at the anode, where it combines with the metal to form an oxide film.



		*dyes*



		A dye is a substance that imparts color to a fabric and is resistant to washing. There are three main types of dye: direct dyes combine with the material of the fabric, yielding a colored compound; indirect dyes require the presence of another substance (a mordant), with which the fabric must first be treated; vat dyes are colorless soluble substances that on exposure to air yield an insoluble colored compound.



		Naturally occurring dyes include indigo, madder (alizarin), logwood, and cochineal, but industrial dyes (introduced in the 19th century) are usually synthetic: acid green was developed in 1835 and bright purple in 1856. Synthetic dyes now allow an almost infinite range of colors to be applied to a wide variety of materials.



		Industrial dyes include azo dyestuffs, acridine, anthracene, and aniline.

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		Chemistry Chronology

Chemistry Chronology

c. 1500 B.C.

The liquid metal mercury is known to the Egyptians who place it in a tomb about this date. It is also known to the Chinese and Hindus.

c. 1000 B.C.

The following elements are known by this date: carbon, copper, gold, iron, lead, mercury, silver, sulfur, tin, zinc.

c. 230 B.C.

Copper-lined pottery jars, with asphalt plugs, containing metal rods—the first electric battery—are used in Baghdad to coat objects with thin layers of gold or silver—the first example of electroplating.

c. 100 B.C.

The Romans produce mercury by heating the sulfide mineral cinnabar and condensing the vapors.

c. 100

Mary the Jewess, an alchemist, succeeds in her laboratory inventions with metals and lays the foundation for later work in chemistry. She creates the world's first distillation device, a double boiler, a way to capture vapors of metals, and a metal alloy called Mary's Black.

297

The tomb of a Chinese military commander of this date contains metal belt ornaments made of aluminum, not isolated by Western scientists until 1827.

742

The most famous alchemist of the period, Jabir ibn-Hayyan of Kufa (Geber in Iraq) practices as a physician at Kufa, Persia. He becomes court physician to the caliph Harun ar-Rashid. He is said to have been the first person to manufacture mineral acids (nitric acid, etc.).

1044

The Chinese text Wu Ching Tsung Yao is written, including a recipe for black powder which uses a mix of saltpeter (potassium nitrate), charcoal, and sulfur to produce the earliest form of gunpowder.

1126

Gunpowder is first record in military use during the siege of Kaifeng, China, capital of the Chinese Sung dynasty. It is used by troops of the rival Jin dynasty.

1249

The English monk and scholar Roger Bacon records the use of explosives, and documents a recipe for gunpowder (possibly his own invention). He writes this dangerous information in coded form .

c. 1313

The German Grey Friar Berthold der Schwarze is traditionally credited with the independent invention of gunpowder. He is also said to have cast the first bronze cannon.

1597

The German scientist and alchemist Andreas Libavius publishes his Alchymia/Alchemy, an outline of chemistry as used in medicine at the time, which also describes the metal zinc.

1648

German chemist Johann Glauber creates nitric acid from the reaction of potassium nitrate and sulfuric acid.

1649

Arsenic is first isolated and identified as an element by German pharmacist Johann Schroeder.

1661

Anglo-Irish chemist and physicist Robert Boyle publishes The Sceptical Chymist, in which he proposes a corpuscular or atomic theory of matter, introducing the modern concept of chemical elements, and distinguishing alkali and acid properties.

1665

Using vacuum pumps, Boyle proves that air is necessary for candles to burn and for animals to live.

1669

Phosphorus is isolated from urine by German alchemist Hennig Brand. He names it "light-bearer" because it glows in the dark.

1670

Boyle discovers hydrogen, produced when certain metals react with acid, although he does not identify it as an element.

March 1676

French physicist Edmé Mariotte discovers the relationship between volume and pressure in a fixed mass of gas, independently of Robert Boyle.

1680

Boyle obtains the element phosphorus by evaporating urine and distilling the residue with sand.

1680

Boyle invents the match, striking a sulfur-tipped splinter of wood against phosphorus-coated paper.

1700

French chemist and physician Nicolas Lemery shows that a mixture of hydrogen and air detonates on the application of a spark or flame, although he does not identify hydrogen as a separate element.

1718

French chemist Etienne Geoffroy presents his tables des rapports ("tables of affinities") to the French Academy of Sciences—the first systematic record of the chemical reactivity of elements and compounds.

1724

Dutch chemist Herman Boerhaave publishes a pioneer study of organic chemistry.

1730

Zinc smelting is first practiced in England, by William Champion of Bristol.

1750

British chemist William Brownrigg first identifies the metal platinum as a separate and distinct element.

1751

Swedish mineralogist Axel Cronstedt isolates nickel from its ore niccolite. He names the pure material Kupfernickel, or "devil's copper."

1755

Scottish chemist Joseph Black discovers carbon dioxide, which he calls "fixed air."

1766

English natural philosopher Henry Cavendish discovers hydrogen and delivers papers to the Royal Society, London, England, on the chemistry of gases.

1772

Scottish chemist Daniel Rutherford discovers nitrogen.

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1772	Swedish chemist Karl Wilhelm Scheele advances the concept of oxygen two years before the English chemist Joseph Priestley.
Aug 1, 1774	English clergyman, chemist, and natural philosopher Joseph Priestley discovers oxygen, which he calls "dephlogisticated air."
1774	French chemist Antoine-Laurent Lavoisier demonstrates the conservation of mass in chemical reactions.
1774	Scheele discovers chlorine and baryta (barium oxide).
1777	Lavoisier shows that air is made up of a mixture of gases, and that one of them (oxygen) is the substance necessary for combustion and rusting to take place. He also assigns the name "oxygen" to Joseph Priestley's dephlogisticated air.
1777	Scheele discovers that silver nitrate, when exposed to light, results in a blackening effect, an important discovery for the development of photography.
1787	French physicist Jacques Charles discovers Charles's law, stating that the volume of a given mass of gas at constant pressure is directly proportional to its absolute temperature (temperature in kelvin).
1789	German chemist Martin Heinrich Klaproth discovers uranium and zirconium.
April 9, 1800	English chemist Humphry Davy details the effects of nitrous oxide, later used as the first anesthetic.
1800	Italian physicist Alessandro Volta invents the voltaic pile made of disks of silver and zinc—the first battery.
1801	English chemist and physicist John Dalton formulates the law of partial pressure in gases—Dalton's Law—that states that each component of a gas mixture produces the same pressure as if it occupied the container alone.
1802	French chemist and physicist Joseph-Louis Gay-Lussac demonstrates that all gases expand by the same fraction of their volume when subjected to the same temperature increase; it permits the establishment of a new temperature scale.
1803	Dalton formulates his atomic theory of matter: that all elements are made of minute indestructible particles, called atoms, that are all identical.
1803	Dalton devises a system of chemical symbols and arranges the relative weights of atoms in a table.
1804	Dalton proposes the law of multiple proportions that states that when two elements combine to form more than one compound the weights of one element combine with a fixed weight of the other in a ratio of small whole numbers. The law provides strong support for his atomic theory.
1805	Gay-Lussac determines the relative proportions of hydrogen and oxygen in water by measuring the proportions of the gases that combine.
Dec 31, 1808	French chemist Joseph-Louis Gay-Lussac, in The Combination of Gases, announces that gases combine chemically in simple proportions of volumes, and that the contraction in volume observed when they combine is a simple relation to the original volume of the gases—Gay-Lussac's Law.
1808	Davy isolates the alkaline-earth metals magnesium, calcium, strontium, and barium.
1811	Italian physicist Amedeo Avogadro hypothesizes that equal volumes of gases at the same temperature and pressure contain equal numbers of molecules.
1811	Swedish chemist Jöns Jakob Berzelius introduces the modern system of chemical symbols.
1819	French physicists Pierre-Louis Dulong and Alexis-Thérèse Petit formulate the Dulong-Petit Law that states that the specific heat of an element, times its atomic weight, is a constant. It proves useful in establishing atomic weights.
1825	Danish scientist Hans Christian Oersted isolates aluminum in powdered form.
1827	Robert Brown observed that very fine pollen grains suspended in water move about in a continuously agitated manner. This became known as Brownian movement.
1828	German chemist Friedrich Wöhler synthesizes urea from ammonium cyanate. It is the first synthesis of an organic substance from an inorganic compound and signals the beginning of organic chemistry.
1829	Scottish chemist Thomas Graham formulates the law named for him on the diffusion rates of gases. He also devises a dialysis method of separating colloids from crystalloids and thereby establishes the science of colloidal chemistry.
1830	French chemist Jean-Baptiste-André Dumas discovers a method of burning organic compounds to determine their nitrogen content.
1831	Peregrine Phillips develops the contact process for producing sulfuric acid.
1836	English chemist John Frederic Daniell invents the Daniell cell, a battery that generates a steady current during continuous operation—an improvement over the voltaic cell which loses power over time.
1837	German chemist Karl Friedrich Mohr enunciates the theory of conservation of energy.
1845	German chemist Hermann Kolbe synthesizes acetic acid from carbon disulfide—the first organic compound to be synthesized from inorganic materials.

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1858	English chemists W. H. Perkin and B. F. Duppa synthesize glycine, the first amino acid to be manufactured.
1858	German chemist Friedrich Kekulé shows that carbon atoms can link together to form long chains—the basis of organic molecules.
1858	Italian chemist Stanislao Cannizzaro differentiates the atomic and molecular weight of an element. It becomes generally accepted in 1860.
1861	Belgian chemist Ernest Solvay patents a method for the economic production of sodium carbonate (washing soda) from sodium chloride, ammonia, and carbon dioxide. Used to make paper, glass, and bleach, and to treat water and refine petroleum, it is a key development in the Industrial Revolution. The first production plant is established in 1863.
1863	English chemist John Newlands develops the first periodic system. It is later adapted by Russian chemist Dmitry Ivanovich Mendeleyev.
1865	Kekulé suggests that the benzene molecule has a six-carbon ring structure. His theory refines current knowledge of organic chemistry.
1867	Swedish chemist Alfred Nobel patents dynamite. It consists of 75% nitroglycerin and 25% of an absorbent material known as ghur which makes the explosive safe and easy to handle.
1869	Based on the fact that the elements exhibit recurring patterns of properties when placed in order of increasing atomic weight, Russian chemist Dmitry Ivanovich Mendeleyev develops the periodic classification of the elements. He leaves gaps for elements yet to be discovered.
1869	U.S. scientist John Wesley Hyatt, in an effort to find a substitute for the ivory in billiard balls, invents (independently of Alexander Parkes) celluloid. The first artificial plastic, it can be produced cheaply in a variety of colors, is resistant to water, oil, and weak acids, and quickly finds use in making such things as combs, toys, and false teeth.
1871	Austrian physicist Ludwig Boltzmann describes the general statistical distribution of energies among the molecules in a gas.
1876	U.S. physicist Josiah Willard Gibbs publishes "On the Equilibrium of Heterogeneous Substances," which lays the theoretical foundation of physical chemistry.
1881	Dutch physicist Johannes van der Waals develops a version of the gas law, now known as the van der Waals equation, which takes into account the size and attraction of atoms and molecules.
1883	English physicist and chemist Joseph Wilson Swan patents a method of creating nitrocellulose (cellulose nitrate) fiber by squeezing it though small holes. It becomes a basic process in the artificial textile industry.
May 1884	Swedish chemist Svante August Arrhenius suggests that electrolytes (solutions or molten compounds that conduct electricity) disassociate into ions (atoms or groups of atoms that carry an electrical charge).
1885	French horticulturist Pierre-Marie-Alexis Millardet develops Bordeaux Mixture, a blend of copper sulfate and hydrated lime. The first successful fungicide, it rapidly achieves worldwide usage.
1886	Arrhenius introduces the idea that acids are substances that disassociate in water to yield hydrogen ions (H+) and that bases are substances that disassociate to yield hydroxide ions (OH–), thus explaining the properties of acids and bases through their ability to yield ions.
1886	U.S. chemist Charles Martin Hall and French chemist Paul-Louis-Toussaint Héroult, working independently, each develop a method for the production of aluminum by the electrolysis of aluminum oxide. The process reduces the price of the metal dramatically and brings it into widespread use.
1898	French chemists Pierre and Marie Curie discover the radioactive elements radium and polonium. Radium is discovered in pitchblende and is the first element to be discovered radiochemically.
1901	Dutch chemist Jacobus van't Hoff receives the first Nobel Prize for Chemistry for his discovery of the laws of chemical dynamics and osmotic pressure.
1901	German engineer Carl von Linde separates liquid oxygen from liquid air. It leads to the widespread use of oxygen in industry.
1902	German chemists Emil Féscher and Franz Hofmeister discover that proteins are polypeptides consisting of amino acids.
1903	Scottish chemist William Ramsay shows that helium is produced during the radioactive decay of radium—an important discovery for the understanding of nuclear reactions.
1906	English physicist Frederick Soddy discovers that ionium and radiothorium, are chemically indistinguishable variants of thorium but have different radioactive properties. He later calls them isotopes.
1907	German chemist Emil Fischer, describes the synthesis of amino acid chains in proteins.
1908	Belgian-born U.S. chemist Leo H. Baekeland invents the plastic Bakelite: its insulating and malleable properties, combined with the fact that it does not bend when heated, ensures it has many uses.
1909	Danish biochemist Søren Sørensen devises the pH scale for measuring acidity and alkalinity.
1911–13	New Zealand-born British physicist Ernest Rutherford and English physicist Henry Moseley showed that practically the whole mass of any atom is concentrated in an extremely small central nucleus bearing a positive electrical charge. Around the nucleus move an equal number of electrons at a relatively great distance. Mosely draws up the periodic table, based on atomic numbers, that is in use today.

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1913	Danish scientist Niels Bohr proposes that the electrons move in orbits around the nucleuslike planets round the sun, and suggests how atoms might emit or absorb light.
1916	U.S. chemist Gilbert Lewis states a new valence theory, in which electrons are shared between atoms.
1923	Danish chemist Johannes Brønsted and British chemist Thomas Martin Lowry simultaneously and independently introduce the idea that an acid tends to lose a proton and a base tends to gain a proton.
1923	Dutch chemist Peter Debye and German chemist Erich Hückel demonstrate that the disassociation of positive and negative ions of salts in solution is complete and not partial.
1925	Austrian physicist Wolfgang Pauli discovers the exclusion principle.
1926	Debye proposes a method of obtaining temperatures a fraction of a degree above absolute zero by removing their magnetic field. Canadian-born U.S. scientist William Giauque independently proposes the same idea the following year.
1928	Polyvinyl chloride (PVC) is developed, simultaneously, by the U.S. companies Carbide and Carbon Corporation and du Pont and the German firm I. G. Farben.
1932	British physicist James Chadwick bombards beryllium with alpha-particles and produces neutral particles, which he called neutrons.
1934	French physicists Frédéric and Irène Joliot-Curie bombard boron, aluminum, and magnesium with alpha particles and obtain radioactive isotopes of nitrogen, phosphorus, and aluminum—elements that are not normally radioactive. They are the first radioactive elements to be prepared artificially.
1935	Chemists working for the British company Imperial Chemical Industries (ICI) polymerize ethylene to make polyethylene, the first true plastic.
c. 1936	Catalytic cracking, a chemical process in which long-chain hydrocarbon molecules are borken down into smaller ones, is introduced to produce gasoline from low-grade crude oil by the U.S. Sun Oil Company and Socony-Vacuum Company.
1938	German physicists Lise Meitner, Otto Hahn, and Fritz Strassmann conclude that bombarding uranium atoms with neutrons splits the atom and releases huge amounts of energy by the conversion of some of the mass of the uranium atom into energy.
1938	The Soviet physicist Pyotr Kapitza discovers that liquid helium exhibits superfluidity, the ability to flow over its containment vessel without friction, when cooled below 2.18K/–270.97°C/519.7°F.
1940	U.S. physicist J. R. Dunning leads a research team that uses a gaseous diffusion technique to isolate uranium-235 from uranium-238. Because uranium-235 readily undergoes fission into two atoms, and in doing so releases large amounts of energy, it is used for fueling nuclear reactors.
1940	U.S. physicists Edwin McMillan and Philip Abelson synthesize the first transuranic element, neptunium, by bombarding uranium with neutrons at the cyclotron at Berkeley, California.
1944	British chemists Archer J. P. Martin and Richard L. M. Synge separate amino acids by using a solvent in a column of silica gel. The beginnings of partition chromatography, the technique leads to further advances in chemical, medical, and biological research.
1946	U.S. physicists Edward Mills Purcell and Felix Bloch independently discover nuclear magnetic resonance, which is used to study the structure of pure metals and composites.
1947	U.S. physicist Willard Libby develops carbon-14 dating.
1962	English chemist Neil Bartlett prepares xenon hexafluoroplatinate, the first compound of an inert gas.
1973	U.S. biochemists Stanley Cohen and Herbert Boyer develop the technique of recombinant DNA (deoxyribonucleic acid). Strands of DNA are cut by restriction enzymes from one species and then inserted into the DNA of another; this marks the beginning of genetic engineering.
1974	Mexican chemist Mario Molina and U.S. chemist F. Sherwood Rowland warn that the chlorofluorocarbons (CFCs) used in refrigerators and as aerosol propellants may be damaging the atmosphere's ozone layer that filters out much of the sun's ultraviolet radiation.
Aug 28, 1976	Indian-born U.S. biochemist Har Gobind Khorana and his colleagues announce the construction of the first artificial gene to function naturally when inserted into a bacterial cell. This is a major breakthrough in genetic engineering.
1977	English biochemist Frederick Sanger describes the full sequence of 5,386 bases in the DNA (deoxyribonucleic acid) of virus phiX174 in Cambridge, England; the first sequencing of an entire genome.
1981	French researchers Claude Michel and Bernard Reveau synthesize some metallic oxides that have excellent conducting properties; the materials prove invaluable in achieving superconductivity at relatively high temperatures.
1985	English chemists Harold Kroto and David Walton and U.S. chemist Richard Smalley discover a new unusually stable elemental form of solid carbon made up of closed cages of 60 carbon atoms shaped like soccer balls; they call them buckminsterfullerines or "buckyballs."

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1988	Dutch firm CCA Biochem develops the biodegradable polymer polyactide; capable of being broken down by human metabolism, it is ideal for use in suturing threads, bone platelets, and artificial skin.
1990	The British company Imperial Chemical Industries (ICI) develops the first practical biodegradable plastic, Biopal.
1993	The first pictures of individual atoms, obtained by the use of a scanning tunneling microscope, are published.
Oct 1994	Ununnilium is discovered by researchers at the heavy-ion cyclotron based at Darmstadt, Germany. It lasts for a millisecond.
Dec 1994	Unununium is discovered by researchers at the heavy-ion cyclotron based in Darmstadt, Germany.
Feb 1996	Element no. 112 is discovered at the GSI heavy-ion research center, Darmstadt, Germany. A single atom is created, which lasts for a third of a millisecond.



		Biographies



		Accum, Friedrich Christian (1769–1838) German chemist who introduced illumination by gas in 1815.



		Achard, Franz Karl (1753–1821) German chemist who was largely responsible for developing the industrial process by which table sugar (sucrose) is extracted from sugar beet.



		Adams, Roger (1889–1971) U.S. organic chemist, known for his painstaking analytical work to determine the composition of naturally occurring substances such as complex vegetable oils and plant alkaloids.



		Alder, Kurt (1902–1958) German organic chemist who with Otto Diels developed the diene synthesis in 1928, a fundamental process that has become known as the Diels—Alder reaction. It is used in organic chemistry to synthesize cyclic (ring) compounds.



		Altman, Sidney (1939–) Canadian-born U.S. biochemist who shared the Nobel Prize for Chemistry in 1989 with Thomas Cech for his research on the catalytic activities of RNA.



		Andrews, Thomas (1813–1885) Irish physical chemist, best known for postulating the idea of critical temperature and pressure from his experimental work on the liquefaction of gases.



		Anfinsen, Christian Boehmer (1916–) U.S. biochemist who shared the Nobel Prize for Physiology or Medicine in 1972 with Stanford Moore and William Stein for his work on the shape and primary structure of ribonuclease (the enzyme that hydrolyses RNA).

Dissociation of Substances Dissolved in Water by Svante Arrhenius
http://dbhs.wvusd.k12.ca.us/Chem-History/Arrhenius-dissociation.html

Extract from the above paper Arrhenius discusses the dissociation of certain substances in water, an observation which led to deductions on electrolysis and his Nobel prize in 1903.



		Arrhenius, Svante August (1859–1927) Swedish scientist, the founder of physical chemistry. For his study of electrolysis, he received the Nobel Prize for Chemistry in 1903. In 1905 he predicted global warming as a result of carbon dioxide emission from burning fossil fuels.



		Baekeland, Leo Hendrik (1863–1944) Belgian-born U.S. chemist. He invented Bakelite, the first commercial plastic, made from formaldehyde (methanal) and phenol. He also made a photographic paper, Velox, which could be developed in artificial light.



		Baeyer, Johann Friedrich Wilhelm Adolf von (1835–1917) German organic chemist who synthesized the dye indigo in 1880.



		Baker, Henry (1698–1774) English scientist who wrote two popular instructional books on the use of the microscope in natural history, and made observations on the crystallization of salts in 1744.



		Bartlett, Neil (1932–) British-born U.S. chemist. In 1962 he prepared the first compound of one of the inert gases, which were previously thought to be incapable of reacting with anything.



		Barton, Derek Harold Richard (1918–) English organic chemist who investigated the stereochemistry of natural compounds.



		Berg, Paul (1926–) U.S. molecular biologist. In 1972, using gene-splicing techniques developed by others, Berg spliced and combined into a single hybrid the DNA from an animal tumor virus (SV40) and the DNA from a bacterial virus.



		Bergius, Friedrich Karl Rudolph (1884–1949) German research chemist who invented processes for converting coal into oil and wood into sugar. He shared a Nobel prize in 1931 with Carl Bosch for his part in inventing and developing high-pressure industrial methods.



		Bergstrom, Sune Karl (1916–) Swedish biochemist who shared the Nobel Prize for Physiology or Medicine in 1982 with John Vane and Bengt Samuelsson for the purification of prostaglandins.



		Berthelot, Pierre Eugene Marcellin (1827–1907) French chemist and politician who carried out research into dyes and explosives, proving that hydrocarbons and other organic compounds can be synthesized from inorganic materials.



		Berthollet, Claude Louis, Count (1748–1822) French chemist who carried out research into dyes and bleaches (introducing the use of chlorine as a bleach) and determined the composition of ammonia.

Page 105



		Berzelius, Jöns Jakob (1779–1848) Swedish chemist. He accurately determined more than 2,000 relative atomic and molecular masses. In 1813–14 he devised the system of chemical symbols and formulas now in use.



		Bloch, Konrad (1912–) German-born U.S. chemist whose research concerned cholesterol.



		Bosch, Carl (1874–1940) German metallurgist and chemist. He developed the Haber process from a small-scale technique for the production of ammonia into an industrial high-pressure process.



		Boyle, Robert (1627–1691) Irish chemist and physicist who published the seminal The Sceptical Chymist in 1661. He formulated (Boyle's law in 1662. He was a pioneer in the use of experiment and scientific method.



		Boyle questioned the alchemical basis of the chemical theory of his day and taught that the proper object of chemistry was to determine the compositions of substances. The term "analysis" was coined by Boyle and many of the reactions still used in qualitative work were known to him. He introduced certain plant extracts, notably litmus, for the indication of acids and bases. He was also the first chemist to collect a sample of gas.



		Bredig, Georg (1868–1944) German physical chemist who devised a method of preparing colloidal solutions in 1898



		Brønsted, Johannes Nicolaus (1879–1947) Danish physical chemist whose work in solution chemistry, particularly electrolytes, resulted in a new theory of acids and bases, the theory of proton donors and proton acceptors, published in 1923.



		Brown, Herbert Charles (1912–) U.S. inorganic chemist who is noted for his research on boron compounds.



		Buchner, Eduard (1860–1917) German chemist who researched the process of fermentation.



		Bunsen, Robert Wilhelm (1811–1899) German chemist credited with the invention of the Bunsen burner. His name is also given to the carbon-zinc electric cell, which he invented in 1841 for use in arc lamps.



		Butenandt, Adolf Friedrich Johann (1903–1995) German biochemist who isolated the first sex hormones (estrone, androsterone, and progesterone), and determined their structure. He shared the 1939 Nobel Prize for Chemistry with Leopold Ruzicka (1887–1976).



		Calvin, Melvin (1911–1997) U.S. chemist who, using radioactive carbon-14 as a tracer, determined the biochemical processes of photosynthesis, in which green plants use chlorophyll to convert carbon dioxide and water into sugar and oxygen.



		Cannizzaro, Stanislao (1826–1910) Italian chemist who revived interest in the work of Avogadro that had, in 1811, revealed the difference between atoms and molecules, and so established atomic and molecular weights as the basis of chemical calculations.



		Carothers, Wallace Hume (1896–1937) U.S. chemist who carried out research into polymerization and, with Paul Flory, invented nylon.



		Carr, Emma Perry (1880–1972) U.S. chemist who in the USA pioneered techniques to synthesize and analyze the structure of complex organic molecules using absorption spectroscopy.



		Cavendish, Henry (1731–1810) English physicist and chemist. He discovered hydrogen (which he called "inflammable air") in 1766, and determined the compositions of water and of nitric acid.



		Cavendish demonstrated in 1784 that water is produced when hydrogen burns in air, thus proving that water is a compound and not an element. He also worked on the production of heat and determined the freezing points for many materials, including mercury.



		Cech, Thomas (1947–) U.S. biochemist who discovered the catalytic activity of RNA.



		Chardonnet, (Louis-Marie) Hilaire Bernigaud, comte de (1839–1924) French chemist who developed artificial silk in 1883, the first artificial fiber.



		Chargaff, Erwin (1905–) Czech-born U.S. biochemist, best known for his work on the base composition of deoxyribonucleic acid (DNA).



		Chevreul, Michel-Eugène (1786–1889) French chemist who studied the composition of fats and identified a number of fatty acids, including "margaric acid," which became the basis of margarine.



		Claude, Georges (1870–1960) French industrial chemist, responsible for inventing neon signs.



		Cleve, Per Teodor (1840–1905) Swedish chemist and geologist who discovered the elements holmium and thulium in 1879.



		Corey, Elias James (1928–) U.S. organic chemist who received the Nobel Prize for Chemistry in 1990 for the development of retrosynthetic analysis, a method of synthesizing complex substances.



		Cornforth, John Warcup (1917–) Australian chemist. Using radioisotopes as markers, he found out how cholesterol is manufactured in the living cell and how enzymes synthesize chemicals that are mirror images of each other (optical isomers).



		Coulson, Charles Alfred (1910–1974) English theoretical chemist. He developed a molecular orbital theory, which is an extension of atomic quantum theory.



		Cram, Donald James (1919–) U.S. chemist who shared the 1987 Nobel Prize for Chemistry with Jean-Marie Lehn and Charles J. Pedersen for their work on molecules with highly selective structure-specific interactions.



		Crookes, William (1832–1919) English scientist whose many chemical and physical discoveries include the metallic element thallium in 1861, the radiometer in 1875, and the Crookes high-vacuum tube used in X-ray techniques. Knighted in 1897.

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		Curie, Marie (1867–1934), born Manya Sklodowska, Polish scientist who, with husband Pierre Curie, discovered in 1898 two new radioactive elements in pitchblende ores: polonium and radium. They isolated the pure elements in 1902. Both scientists refused to take out a patent on their discovery and were jointly awarded the Nobel Prize for Physics in 1903, with Henri Becquerel. Marie Curie was also awarded the Nobel Prize for Chemistry in 1911.



		Curie, Pierre (1859–1906) French scientist. He shared the Nobel Prize for Physics in 1903 with his wife Marie Curie and Henri Becquerel. From 1896 the Curies had worked together on radioactivity, discovering two radioactive elements.



		Dalton, John (1766–1844) English chemist who proposed the theory of atoms, which he considered to be the smallest parts of matter. He produced the first list of atomic weights in "Absorption of Gases" in 1805 and put forward the law of partial pressures of gases (Dalton's law).



		Davy, Humphry (1778–1829) English chemist. He discovered, by electrolysis, the metallic elements sodium and potassium in 1807, and calcium, boron, magnesium, strontium, and barium in 1808. In addition, he established that chlorine is an element and proposed that hydrogen is present in all acids. He invented the safety lamp for use in mines where methane was present, enabling miners to work in previously unsafe conditions.



		Deisenhofer, Johann (1943–) German chemist who was the first to apply the technique of X-ray crystallography (the use of X-rays to discern atomic structure) to biological molecules.



		Dewar, James (1842–1923) Scottish chemist and physicist who invented the vacuum flask.



		Diels, Otto Paul Hermann (1876–1954) German chemist. In 1950 he and his former assistant, Kurt Alder, were jointly awarded the Nobel Prize for Chemistry for their research into the synthesis of organic chemical compounds.



		Domagk, Gerhard Johannes Paul (1895–1964) German pathologist, discoverer of antibacterial sulfonamide drugs.



		Dulong, Pierre Louis (1785–1838) French chemist and physicist. In 1819 he discovered, together with physicist Alexis Petit, the law that now bears their names.



		Dumas, Jean Baptiste André (1800–1884) French chemist. He made contributions to organic analysis and synthesis, and to the determination of atomic weights (relative atomic masses) through the measurement of vapor densities.



		Eigen, Manfred (1927–) German chemist who worked on extremely rapid chemical reactions (those taking less than 1 millisecond).



		Emeléus, Harry Julius (1903–) English chemist. He made wide-ranging investigations in inorganic chemistry, studying particularly nonmetallic elements and their compounds.



		Ernst, Richard Robert (1933–) Swiss physical chemist who improved the technique of nuclear magnetic resonance (NMR) spectroscopy.



		Eyde, Samuel (1866–1940) Norwegian industrial chemist. He helped to develop a commercial process for the manufacture of nitric acid that made use of comparatively cheap hydroelectricity.



		Fajans, Kasimir (1887–1975) Polish-born U.S. chemist. He did pioneering work on radioactivity and isotopes, he also formulated rules that help to explain valence and chemical bonding.



		Faraday, Michael (1791–1867) English chemist and physicist. Faraday isolated benzene from gas oils and produced the basic laws of electrolysis in 1834. Faraday's laws of electrolysis established the link between electricity and chemical affinity, one of the most fundamental concepts in science.

Electrical Decomposition by Michael Faraday
http://dbhs.wvusd.k12.ca.us/Chem-History/Faraday-electrochem.html

Transcript of Faraday's paper in Philosophical Transactions of the Royal Society, 1834, in which Faraday describes for the first time the phenomenon of electrolysis.



		Fischer, Edmond (1920–) U.S. biochemist who shared the 1992 Nobel Prize for Physiology or Medicine with Edwin Krebs for isolating and describing the action of the enzymes responsible for reversible protein phosphorylation.



		Fischer, Emil Hermann (1852–1919) German chemist who produced synthetic sugars and, from these, various enzymes.



		Fischer, Ernst Otto (1918–) German inorganic chemist. He showed that transition metals can bond chemically to carbon.



		Fischer, Hans (1881–1945) German chemist awarded a Nobel prize in 1930 for his work on hemoglobin, the oxygencarrying red coloring matter in blood.



		Fischer, Hermann Otto Laurenz (1888–1960) German organic chemist. He carried out research into the synthetic and structural chemistry of carbohydrates, glycerides, and inositols.



		Flory, Paul John (1910–1985) U.S. polymer chemist. He was awarded the 1974 Nobel Prize for Chemistry for his investigations of synthetic and natural macromolecules. With Wallace Carothers, he developed nylon, the first synthetic polyamide.



		Freundlich, Herbert Max Finlay (1880–1941) German physical chemist. He worked on the nature of colloids, particularly sols and gels and introduced the term "thixotropy" to describe the behavior of gels.



		Friedel, Charles (1832–1899) French organic chemist and mineralogist. Together with U.S. chemist James Mason Crafts (1839–1917) he discovered the Friedel—Crafts reaction which uses aluminum chloride as a catalyst to facilitate the addition of an alkyl halide (halogenoalkane) to an aromatic compound.



		Fröhlich, Herbert (1905–1991) German-born British physicist who helped lay the foundations for modern theoretical physics in the UK.

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		Fukui, Kenichi (1918–1998) Japanese industrial chemist who shared the Nobel Prize for Chemistry in 1981 with Roald Hoffman for his work on "frontier orbital theory", predicting the change in molecular orbitals (the arrangement of electrons around the nucleus during chemical reactions).



		Funk, Casimir (1884–1967) Polish-born U.S. biochemist who pioneered research into vitamins.



		Geber, Latinized form of Jabir ibn Hayyan (c. 721–c. 776) Arabian alchemist. His influence lasted for more than six hundred years.



		Giauque, William Francis (1895–1982) Canadian-born U.S. physical chemist who specialized in chemical thermodynamics, in particular the behavior of matter at extremely low temperatures.



		Gibbs, Josiah Willard (1839–1903) U.S. theoretical physicist and chemist who developed a mathematical approach to thermodynamics and established vector methods in physics. He devised the phase rule and formulated the Gibbs adsorption isotherm.

Gibbs, Josiah
http://www.history.mcs.st-and.ac.uk/~history/Mathematicians/Gibbs.html

Photograph and biography of the 19th-century U.S. mathematician. This site, run by St. Andrews University, also provides information on Gibbs's constant along with literature references for further study.



		Gilbert, Walter (1932–) U.S. molecular biologist who studied genetic control, seeking the mechanisms that switch genes on and off.



		Gilman, Henry (1893–1986) U.S. organic chemist. He made a comprehensive study of methods of high-yield synthesis, quantitative and qualitative analysis, and uses of organometallic compounds, particularly Grignard reagents.



		Goldschmidt, Victor Moritz (1888–1947) Swiss-born Norwegian chemist. He did fundamental work in geochemistry, particularly on the distribution of elements in the earth's crust.



		Graham, Thomas (1805–1869) Scottish chemist who laid the foundations of physical chemistry by his work on the diffusion of gases and liquids.



		Grignard, (François Auguste) Victor (1871–1935) French chemist. In 1900 he discovered a series of organic compounds, the Grignard reagents, that found applications as some of the most versatile reagents in organic synthesis.



		Haber, Fritz (1868–1934) German chemist whose conversion of atmospheric nitrogen to ammonia opened the way for the synthetic fertilizer industry.



		Hall, Charles Martin (1863–1914) U.S. chemist who developed a process for the commercial production of aluminum in 1886.



		Hammick, Dalziel Llewellyn (1887–1966) English chemist whose major contributions were in the fields of theoretical and synthetic organic chemistry.



		Harden, Arthur (1865–1940) English biochemist who investigated the mechanism of sugar fermentation and the role of enzymes in this process.



		Hassel, Odd (1897–1981) Norwegian physical chemist who established the technique of conformational analysis—the determination of the properties of a molecule by rotating it around a single bond—and received the Nobel Prize for Chemistry in 1969.



		Hauptman, Herbert A (1917–) U.S. mathematician who shared the 1985 Nobel Prize for Chemistry with Jerome Karle for discovering a general method of determining crystal structures by X-ray diffraction.



		Haworth, (Walter) Norman (1883–1950) English organic chemist who was the first to synthesize a vitamin (ascorbic acid, vitamin C) in 1933, for which he shared a Nobel prize in 1937.



		Helmont, Jean Baptiste van (1579–1644) Flemish physician who was the first to realize that there are gases other than air, and claimed to have coined the word "gas" (from Greek cháos).



		Henry, William (1774–1836) English chemist and physician. In 1803 he formulated Henry's law, which states that when a gas is dissolved in a liquid at a given temperature, the mass that dissolves is in direct proportion to the pressure of the gas.



		Herschbach, Dudley R. (1932–) U.S. chemist who shared the 1986 Nobel Prize for Chemistry with Yuan T. Lee and John C. Polanyi for their researches into the dynamics of the processes which occur when atoms and molecules react.



		Hess, Germain Henri (1802–1850) Swiss-born Russian chemist, a pioneer in the field of thermochemistry. The law of constant heat summation is named for him.



		Hevesy, Georg Karl von (1885–1966) Hungarian-born Swedish chemist, discoverer of the element hafnium. He was the first to use a radioactive isotope to follow the steps of a biological process.



		Heyrovsky, Jaroslav (1890–1967) Czech chemist who was awarded the 1959 Nobel prize for his invention and development of polarography, an electrochemical technique of chemical analysis.



		Hinshelwood, Cyril Norman (1897–1967) English chemist who shared the 1956 Nobel prize for his work on chemical chain reactions.



		Hodgkin, Dorothy Mary Crowfoot (1910–1994) English biochemist who analyzed the structure of penicillin, insulin, and vitamin B12.



		Hoffman, Roald (1937–) Polish chemist who worked on molecular orbital theory with Robert Woodward and developed the Woodward-Hoffman rules for the conservation of orbital symmetry.



		Hofmann, August Wilhelm von (1818–1892) German chemist who studied the extraction and exploitation of coal-tar derivatives, mainly for dyes.



		Huber, Robert (1937–) German chemist who shared the Nobel Prize for Chemistry in 1988 with Hartmut Michel and

Page 108



		Johann Deisenhofer for his use of high resolution X-ray crystallography.



		Hückel, Erich Armand Arthur Joseph (1896–1980) German physical chemist who, with Peter Debye, developed in 1923 the modern theory that accounts for the electrochemical behavior of strong electrolytes in solution.



		Hyatt, John Wesley (1837–1920) U.S. inventor who in 1869 invented celluloid, the first artificial plastic, intended as a substitute for ivory.



		Ingold, Christopher Kelk (1893–1970) English organic chemist who specialized in the concepts, classification, and terminology of theoretical organic chemistry.



		Ipatieff, Vladimir Nikolayevich (1867–1952) Russian-born U.S. organic chemist who developed catalysis in organic chemistry, particularly in reactions involving hydrocarbons.



		Karle, Jerome (1918–) U.S. chemist who, with colleague Herbert Hauptman, tested the range of available diffraction techniques, such as X-ray diffraction and the ''heavy atom" technique.



		Karrer, Paul (1889–1971) Russian-born Swiss organic chemist who synthesized various vitamins.



		Kekulé von Stradonitz, Friedrich August (1829–1896) German chemist whose 1858 theory of molecular structure revolutionized organic chemistry.



		Kendrew, John Cowdery (1917–1997) English biochemist who determined the structure of the muscle protein myoglobin.



		Kenyon, Joseph (1885–1961) English organic chemist who studied optical activity, particularly of secondary alcohols.



		Kipping, Frederic Stanley (1863–1949) English chemist who pioneered the study of the organic compounds of silicon; he invented the term "silicone," which is now applied to the entire class of oxygen-containing polymers.



		Klaproth, Martin Heinrich (1743–1817) German chemist who first identified the elements uranium and zirconium, in 1789.



		Klug, Aaron (1926–) South African molecular biologist who improved the quality of electron micrographs by using laser lighting.



		Kolbe, (Adolf Wilhelm) Hermann (1818–1884) German chemist, generally regarded as the founder of modern organic chemistry with his synthesis of acetic acid—an organic compound—from inorganic starting materials.



		Kornberg, Arthur (1918–) U.S. biochemist. In 1956 he discovered the enzyme DNA-polymerase, which enabled molecules of the genetic material DNA to be synthesized for the first time.



		Langmuir, Irving (1881–1957) U.S. scientist who invented the mercury vapor pump for producing a high vacuum, and the atomic hydrogen welding process; he was also a pioneer of the thermionic valve.



		Lapworth, Arthur (1872–1941) British chemist, one of the founders of modern physical-organic chemistry. He formulated the electronic theory of organic reactions (independently of Robert Robinson).



		Lavoisier, Antoine Laurent (1743–1794) French chemist. He proved that combustion needs only a part of the air, which he called oxygen, thereby destroying the theory of phlogiston (an imaginary "fire element" released during combustion). With astronomer and mathematician Pierre de Laplace, he showed in 1783 that water is a compound of oxygen and hydrogen.

Lavoisier, Antoine Laurent
http://www.knight.org/advent/cathen/09052a.htm

Account of the life and achievements of the French chemist, philosopher, and economist.



		Leblanc, Nicolas (1742–1806) French chemist who in the 1780s developed a process for making soda ash (sodium carbonate, Na₂CO₃) from common salt (sodium chloride, NaCl).



		Le Châtelier, Henri Louis (1850–1936) French physical chemist who formulated the principle now named for him, which states that if any constraint is applied to a system in chemical equilibrium, the system tends to adjust itself to counteract or oppose the constraint.



		Lee, Yuan Tseh (1936–) Taiwanese chemist who contributed much to the field of chemical reaction dynamics.



		Lehn, Jean-Marie (1939–) French chemist who demonstrated for the first time how metal ions could be made to exist in a nonplanar structure, tightly bound into the cavity of a crown ether molecule.



		Leloir, Luis Frederico (1906–1987) Argentinian chemist who studied glucose metabolism.

G. N. Lewis and the Covalent Bond
http://dbhs.wvusd.kl2.ca.us/Chem-History/Lewis-1916/Lewis-1916.html

Transcript of one of the most important papers in the history of chemistry. In the paper Lewis forwards his ideas on the shared electron bond, later to become known as the covalent bond.



		Lewis, Gilbert Newton (1875–1946) U.S. theoretical chemist who defined a base as a substance that supplies a pair of electrons for a chemical bond, and an acid as a substance that accepts such a pair. He also set out the electronic theory of valence and in thermodynamics listed the free energies of 143 substances.

Libby, Willard Frank
http://kroeber.anthro.mankato.msus.edu/bio/Libby.htm

Profile of the Nobel prizewinning U.S. chemist. It traces his academic career and official appointments and the process which led to his discovery of the technique of radiocarbon dating.



		Libby, Willard Frank (1908–1980) U.S. chemist whose development in 1947 of radiocarbon dating as a means of

Page 109



		determining the age of organic or fossilized material won him a Nobel prize in 1960.



		Liebig, Justus, Baron von (1803–1873) German organic chemist who extended chemical research into other scientific fields, such as agricultural chemistry and biochemistry.



		Lipmann, Fritz Albert (1899–1986) German-born U.S. biochemist. He investigated the means by which the cell acquires energy and highlighted the crucial role played by the energyrich phosphate molecule adenosine triphosphate (ATP).



		Lipscomb, William Nunn (1919–) U.S. chemist who studied the relationships between the geometric and electronic structures of molecules and their chemical and physical behavior.



		Longuet-Higgins, Hugh Christopher (1923–) English theoretical chemist whose main contributions have involved the application of precise mathematical analyses, particularly statistical mechanics, to chemical problems.



		Lonsdale, Kathleen (1903–1971), born Yardley, Irish X-ray crystallographer who was among the first to determine the structures of organic molecules.



		Marcus, Rudolph Arthur (1923–) Canadian chemist who advanced the theory of electron-transfer reactions (involving soluble molecules and/or ions) which drive many biological processes.



		Martin, Archer John Porter (1910–) British biochemist who received the 1952 Nobel Prize for Chemistry for work with Richard Synge on paper chromatography in 1944.



		Mendeleyev, Dmitri Ivanovich (1834–1907) Russian chemist who framed the periodic law in chemistry in 1869, which states that the chemical properties of the elements depend on their atomic weights. This law is the basis of the periodic table of the elements, in which the elements are arranged by atomic number and organized by their related groups.



		Merrifield, R. Bruce (1921–) U.S. chemist who was awarded the 1984 Nobel Prize for Chemistry for his development of a method for synthesizing large organic molecules using a solid support or matrix.



		Meyer, (Julius) Lothar (1830–1895) German chemist who, independently of his Russian contemporary Dmitri Mendeleyev, produced a periodic law describing the properties of the chemical elements.



		Meyer, Viktor (1848–1897) German organic chemist who invented an apparatus for determining vapor densities (and hence molecular weights), now named for him.



		Michel, Hartmut (1948–) German biochemist who worked on determining the molecular structure of photosynthetic reaction centers.



		Mitscherlich, Eilhard (1794–1863) German chemist who discovered isomorphism (the phenomenon in which substances of analogous chemical composition crystallize in the same crystal form). He also synthesized many organic compounds for the first time.



		Molina, Mario (1943–) Mexican chemist who shared the 1995 Nobel Prize for Chemistry with Paul Crutzen and F. Sherwood Rowland for their work in atmospheric chemistry, particularly concerning the formation and decomposition of ozone.



		Müller, Paul Herman (1899–1965) Swiss chemist who discovered the first synthetic contact insecticide, DDT, in 1939.



		Natta, Giulio (1903–1979) Italian chemist who worked on the production of polymers. He shared a Nobel prize in 1963 with German chemist Karl Ziegler.



		Nernst, (Walther) Hermann (1864–1941) German physical chemist who won a Nobel prize in 1920 for work on heat changes in chemical reactions.

Alfred Nobel–His Life and Work
http://www.nobel.se/alfred/biography.html

Presentation of the life and work of Alfred Nobel. The site includes references to Nobel's life in Paris, as well as his frequent travels, his industrial occupations, his scientific discoveries and especially his work on explosives, which led to the patenting of dynamite, his numerous chemical inventions which included materials such as synthetic leather and artificial silk, his interest in literature and in social and peace-related issues, and of course the Nobel prizes which came as a natural extension of his lifelong interests.



		Nobel, Alfred Bernhard (1833–1896) Swedish chemist and engineer. He invented dynamite in 1867, gelignite in 1875, and ballistite, a smokeless gunpowder, in 1887. Having amassed a large fortune from the manufacture of explosives and the exploitation of the Baku oil fields in Azerbaijan, near the Caspian Sea, he left this in trust for the endowment of five Nobel prizes.



		Olah, George Andrew (1927–) Hungarian-born U.S. chemist who was awarded the 1992 Nobel Prize for Chemistry for his isolation of carbocations, electrically charged fragments of hydrocarbon molecules.



		Ostwald, (Friedrich) Wilhelm (1853–1932) Latvian-born German chemist who devised the Ostwald process (the oxidation of ammonia over a platinum catalyst to give nitric acid).



		Pauling, Linus Carl (1901–1994) U.S. theoretical chemist and biologist. His ideas on chemical bonding are fundamental to modern theories of molecular structure.

Dr. Linus Pauling Profile
http://www.achievement.org/autodoc/page/pau0pro-1

Description of the life and works of the multiple Nobel prizewinner also includes a lengthy interview with Dr. Pauling from 1990.



		Pedersen, Charles (1904–1990) U.S. organic chemist who shared the Nobel Prize for Chemistry in 1987 with Jean Lehn and Donald Cram for his discovery of "crown ether," a cyclic polyether.

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		Pelletier, Pierre-Joseph (1788–1842) French chemist whose extractions of a range of biologically active compounds from plants founded the chemistry of the alkaloids. The most important of his discoveries was quinine, used against malaria.



		Perey, Marguerite (Catherine) (1909–1975) French nuclear chemist who discovered the radioactive element francium in 1939.



		Perutz, Max Ferdinand (1914–) Austrian-born British biochemist who shared the 1962 Nobel Prize for Chemistry with his coworker John Kendrew for work on the structure of the hemoglobin molecule.



		Polanyi, John Charles (1929–) German physical chemist whose research on infrared light given off during chemical reactions (infrared chemical luminescence) laid the foundations for the development of chemical lasers.



		Porter, George (1920–) English chemist. From 1947 he and Ronald Norrish developed a technique by which flashes of high energy are used to bring about extremely fast chemical reactions.



		Pregl, Fritz (1869–1930) Austrian chemist who, during his research on bile acids, devised new techniques for microanalysis (the analysis of very small quantities).



		Prelog, Vladimir (1906–1998) Bosnian-born Swiss organic chemist who studied alkaloids and antibiotics.



		Priestley, Joseph (1733–1804) English chemist and Unitarian minister. He identified oxygen in 1774 and several other gases. Dissolving carbon dioxide under pressure in water, he began a European craze for soda water.



		Prigogine, Ilya, Viscount Prigogine (1917–) Russian-born Belgian chemist who, as a highly original theoretician, has made major contributions to the field of thermodynamics.



		Proust, Joseph Louis (1754–1826) French chemist. He was the first to state the principle of constant composition of compounds—that compounds consist of the same proportions of elements wherever found.



		Prout, William (1785–1850) British physician and chemist. In 1815 Prout published his hypothesis that the atomic weight of every atom is an exact and integral multiple of the mass of the hydrogen atom.



		Ramsay, William (1852–1916) Scottish chemist who, with Lord Rayleigh, discovered argon in 1894.



		Raoult, François Marie (1830–1901) French chemist. In 1882, while working at the University of Grenoble, Raoult formulated one of the basic laws of chemistry. Raoult's law enables the molecular weight of a substance to be determined by noting how much of it is required to depress the freezing point of a solvent by a certain amount.



		Regnault, Henri Victor (1810–1878) German-born French physical chemist who showed that Boyle's law applies only to ideal gases.



		Richards, Theodore William (1868–1928) U.S. chemist who determined as accurately as possible the atomic weights of a large number of elements.



		Robertson, Robert (1869–1949) Scottish chemist who worked on explosives for military use, such as TNT.



		Robinson, Robert (1886–1975) English chemist, Nobel prizewinner in 1947 for his research in organic chemistry on the structure of many natural products, including flower pigments and alkaloids. He formulated the electronic theory now used in organic chemistry.



		Rodbell, Martin (1925–) U.S. molecular biochemist who shared the 1994 Nobel Prize for Physiology or Medicine with Alfred Gilman for their discovery of a family of proteins that translate messages from outside a cell into action inside cells.



		Rowland, F. Sherwood (1927–) U.S. chemist who shared the 1995 Nobel Prize for Chemistry with Mario Molina and Paul Crutzen for their work in atmospheric chemistry.



		Ruzicka, Leopold Stephen (1887–1976) Swiss chemist who began research on natural compounds such as musk and civet secretions. Ruzicka shared the 1939 Nobel Prize for Chemistry with Adolf Butenandt.



		Sabatier, Paul (1854–1941) French chemist. He found in 1897 that if a mixture of ethylene and hydrogen was passed over a column of heated nickel, the ethylene changed into ethane.



		Saint-Claire Deville, Henri Etienne (1818–1881) French inorganic chemist who worked on high-temperature reactions and was the first to extract metallic aluminum in any quantity.



		Sanger, Frederick (1918–) English biochemist. He was the first person to win a Nobel Prize for Chemistry twice: the first in 1958 for determining the structure of insulin, and the second in 1980 for work on the chemical structure of genes.



		Scheele, Karl Wilhelm (1742–1786) Swedish chemist and pharmacist who isolated many elements and compounds for the first time, including oxygen in about 1772, and chlorine in 1774.



		Seaborg, Glenn Theodore (1912–) U.S. nuclear chemist. For his discovery of plutonium and research on the transuranic elements, he shared a Nobel prize in 1951 with his co-worker Edwin McMillan.



		Semenov, Nikolai Nikolaevich (1896–1986) Russian physical chemist who studied chemical chain reactions, particularly branched-chain reactions.



		Smalley, Richard E. (1943–) U.S. chemist who, with colleagues Robert Curl and Harold Kroto, discovered buckminsterfullerene (carbon 60) in 1985.



		Soddy, Frederick (1877–1956) English physical chemist who pioneered research into atomic disintegration and coined the term isotope. He was awarded a Nobel prize in 1921 for investigating the origin and nature of isotopes.



		Solvay, Ernest (1838–1922) Belgian industrial chemist who in the 1860s invented the ammonia-soda process, also known as the Solvay process, for making the alkali sodium carbonate.



		Sørensen, Søren Peter Lauritz (1868–1939) Danish chemist who in 1909 introduced the concept of using the pH scale as a measure of the acidity of a solution.

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		Stahl, Georg Ernst (1660–1734) German chemist who developed the theory that objects burn because they contain a combustible substance, phlogiston.



		Stanley, Wendell Meredith (1904–1971) U.S. biochemist who crystallized the tobacco mosaic virus (TMV) in 1935.



		Stas, Jean Servais (1813–1891) Belgian analytical chemist who made the first accurate determinations of atomic weights (relative atomic masses).



		Staudinger, Hermann (1881–1965) German organic chemist, founder of macromolecular chemistry, who carried out pioneering research into the structure of albumen and cellulose.



		Stein, William Howard (1911–1980) U.S. biochemist who determined the amino acid sequence of the enzyme ribonuclease.



		Sumner, James Batcheller (1887–1955) U.S. biochemist. In 1926 he succeeded in crystallizing the enzyme urease and demonstrating its protein nature. For this work Sumner shared the 1946 Nobel Prize for Chemistry with John Northrop and Wendell Stanley.



		Svedberg, Theodor (1884–1971) Swedish chemist. In 1924 he constructed the first ultracentrifuge.



		Synge, Richard Laurence Millington (1914–1994) British biochemist who improved paper chromatography (a means of separating mixtures) to the point where individual amino acids could be identified.



		Taube, Henry (1915–) U.S. chemist who established the basis of inorganic chemistry through his study of the loss or gain of electrons by atoms during chemical reactions.



		Tiselius, Arne Wilhelm Kaurin (1902–1971) Swedish chemist who developed a powerful method of chemical analysis known as electrophoresis.



		Todd, Alexander Robertus (1907–), Baron Todd, Scottish organic chemist who won a Nobel prize in 1957 for his work on the role of nucleic acids in genetics.



		Travers, Morris William (1872–1961) English chemist who, with Scottish chemist William Ramsay, between 1894 and 1908 first identified what were called the inert or noble gases: krypton, xenon, and radon.



		Tswett, Mikhail Semyonovich (1872–1919) Italian-born Russian scientist who made an extensive study of plant pigments and developed the technique of chromatography to separate them.



		Urey, Harold Clayton (1893–1981) U.S. chemist. In 1932 he isolated heavy water and discovered deuterium, for which he was awarded the 1934 Nobel Prize for Chemistry.



		van't Hoff, Jacobus Henricus (1852–1911) Dutch physical chemist. He explained the "asymmetric" carbon atom occurring in optically active compounds and developed the concept of chemical affinity as the maximum work obtainable from a reaction.



		Vauquelin, Louis Nicolas (1763–1829) French chemist who worked mainly in the inorganic field, analyzing minerals. He discovered the elements chromium (1797) and beryllium.



		Virtanen, Artturi Ilmari (1895–1973) Finnish chemist who from 1920 made discoveries in agricultural chemistry.



		Volhard, Jacob (1834–1910) German chemist who devised various significant methods of organic synthesis.



		Wald, George (1906–1997) U.S. biochemist who explored the chemistry of vision.



		Wallach, Otto (1847–1931) German analytic chemist who isolated a new class of compounds, called terpenes, from essential oils (oils extracted from plants and used in medicine, aromatherapy, and perfume).



		Werner, Alfred (1866–1919) French-born Swiss chemist. He was awarded a Nobel prize in 1913 for his work on valence theory, which gave rise to the concept of coordinate bonds and coordination compounds.



		Wieland, Heinrich Otto (1877–1957) German organic chemist who determined the structures of steroids and related compounds.



		Wilkinson, Geoffrey (1921–1996) English inorganic chemist who shared a Nobel prize in 1973 for his pioneering work on the organometallic compounds of the transition metals.



		Willstatter, Richard (1872–1942) German organic chemist who investigated plant pigments—such as chlorophyll—and alkaloids, determining the structure of cocaine, tropine, and atropine.



		Windaus, Adolf Otto Reinhold (1876–1959) German chemist who was awarded the Nobel Prize for Chemistry in 1928 for his research on the structure of cholesterol, its relationship to vitamin D, and his discovery that steroids are precursors of vitamins.



		Wittig, Georg (1897–1987) German chemist whose method of synthesizing alkenes (olefins) from carbonyl compounds is a reaction often termed the Wittig synthesis. For this achievement he shared the 1979 Nobel Prize for Chemistry.



		Wöhler, Friedrich (1800–1882) German chemist who in 1828 became the first person to synthesize an organic compound (urea) from an inorganic compound (ammonium cyanate).



		Wollaston, William Hyde (1766–1828) English chemist and physicist who discovered in 1804 how to make malleable platinum.



		Woodward, Robert Burns (1917–1979) U.S. chemist who worked on synthesizing a large number of complex molecules.



		Wurtz, Charles Adolphe (1817–1884) French organic chemist who discovered a method of producing paraffin hydrocarbons (alkanes) using alkyl halides (haloalkanes) and sodium in ether. The method was named the Wurtz reaction.



		Ziegler, Karl (1898–1973) German organic chemist. In 1963 he shared the Nobel Prize for Chemistry with Giulio Natta of Italy for his work on the chemistry and technology of large polymers.



		Zsigmondy, Richard Adolf (1865–1929) Austrian-born German chemist who devised and built an ultramicroscope in 1903.

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		Glossary



		A



		absolute zero lowest temperature theoretically possible according to kinetic theory, zero kelvin (0 K), equivalent to –273.15°C/–459.67°F, at which molecules are in their lowest energy state. Near absolute zero, the physical properties of some materials change substantially; for example, some metals lose their electrical resistance and become superconducting.



		acid compound that releases hydrogen ions (H+ or protons) in the presence of an ionizing solvent (usually water). Acids react with bases to form salts, and they act as solvents. Strong acids are corrosive; dilute acids have a sour or sharp taste, although in some organic acids this may be partially masked by other flavor characteristics. The strength of an acid is measured by its hydrogen-ion concentration, indicated by the pH value. All acids have a pH below 7.0.



		actinide any of a series of 15 radioactive metallic chemical elements with atomic numbers 89 (actinium) to 103 (lawrencium). Elements 89 to 95 occur in nature; the rest of the series are synthesized elements only. Actinides are grouped together because of their chemical similarities (for example, they are all bivalent), the properties differing only slightly with atomic number. The series is set out in a band in the periodic table of the elements, as are the lanthanides.



		affinity the force of attraction (see bond) between atoms that helps to keep them in combination in a molecule. The term is also applied to attraction between molecules, such as those of biochemical significance (for example, between enzymes and substrate molecules). This is the basis for affinity chromatography, by which biologically important compounds are separated.



		aliphatic compound any organic chemical compound in which the carbon atoms are joined in straight chains, as in hexane (C₆H₁₄), or in branched chains, as in 2-methylpentane (CH₃CH(CH₃)CH₂CH₂CH₃).



		alkali a base that is soluble in water. Alkalis neutralize acids and are soapy to the touch. The strength of an alkali is measured by its hydrogen-ion concentration, indicated by the pH value. They may be divided into strong and weak alkalis: a strong alkali (for example, potassium hydroxide, KOH) ionizes completely when dissolved in water, whereas a weak alkali (for example, ammonium hydroxide, NH₄OH) exists in a partially ionized state in solution. All alkalis have a pH above 7.0.



		The hydroxides of metals are alkalis. Those of sodium and potassium are chemically powerful; both were historically derived from the ashes of plants.



		alkali metal any of a group of six metallic elements with similar chemical properties: lithium, sodium, potassium, rubidium, cesium, and francium.



		alkaline-earth metal any of a group of six metallic elements with similar bonding properties: beryllium, magnesium, calcium, strontium, barium, and radium.



		allotropy property whereby an element can exist in two or more forms (allotropes), each possessing different physical properties but the same state of matter (gas, liquid, or solid). The allotropes of carbon are diamond and graphite. Sulfur has several allotropes (flowers of sulfur, plastic, rhombic, and monoclinic). These solids have different crystal structures, as do the white and gray forms of tin and the black, red, and white forms of phosphorus.



		alpha particle positively charged, high-energy particle emitted from the nucleus of a radioactive atom. It is identical with the nucleus of a helium atom—that is, it consists of two protons and two neutrons. The process of emission, alpha decay, transforms one element into another, decreasing the atomic (or proton) number by two and the atomic mass (or nucleon number) by four.



		aromatic compound organic chemical compound in which some of the bonding electrons are delocalized (shared among several atoms within the molecule and not localized in the vicinity of the atoms involved in bonding).



		assay the determination of the quantity of a given substance present in a sample. Usually it refers to determining the purity of precious metals.



		atom smallest unit of matter that can take part in a chemical reaction, and which cannot be broken down chemically into anything simpler. An atom is made up of protons and neutrons in a central nucleus surrounded by electrons. The atoms of the various elements differ in atomic number, atomic weight, and chemical behavior.



		atomic mass unit, or dalton unit, (symbol amu or u) unit of mass that is used to measure the relative mass of atoms and molecules. It is equal to one-twelfth of the mass of a carbon-12 atom, which is equivalent to the mass of a proton, or 1.66 x 10⁽²⁷ kg. The atomic weight of an atom has no units; thus oxygen-16 has an atomic mass of 16 daltons but an atomic weight of 16.



		atomic number, or proton number, the number (symbol Z) of protons in the nucleus of an atom. It is equal to the positive charge on the nucleus.



		In a neutral atom, it is also equal to the number of electrons surrounding the nucleus. The chemical elements are arranged in the periodic table of the elements according to their atomic number. See also nuclear notation.



		atomic weight the mass of an atom relative to one-twelfth the mass of an atom of carbon-12. It depends primarily on the number of protons and neutrons in the atom, the electrons having negligible mass. If more than one isotope of the element is present, the relative atomic mass is calculated by taking an average that takes account of the relative proportions of each isotope, resulting in values that are not whole numbers.



		Avogadro's hypothesis the law stating that equal volumes of all gases, when at the same temperature and pressure, have the same numbers of molecules. It was first propounded by Amedeo Avogadro.



		B



		base a substance that accepts protons. Bases react with acids to give water and a salt. They may be a soluble oxide,

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		hydroxide (such as sodium hydroxide, NaOH), or compound (such as ammonia, NH₃) that dissolves in water to give the hydroxide ion (OH⁽), or an insoluble oxide or hydroxide (such as copper(II) oxide, CuO) that reacts with an acid. A base that is soluble in water is called an alkali.



		battery any energy-storage device allowing release of electricity on demand. It is made up of one or more electrical cells.



		beta particle electron ejected with great velocity from a radioactive atom that is undergoing spontaneous disintegration. Beta particles do not exist in the nucleus but are created on disintegration, beta decay, when a neutron converts to a proton to emit an electron.



		bond result of the forces of attraction that hold together atoms of an element or elements to form a molecule. The principal types of bonding are ionic, covalent, metallic, and intermolecular (such as hydrogen bonding).



		Boyle's law law stating that the volume of a given mass of gas at a constant temperature is inversely proportional to its pressure. For example, if the pressure of a gas doubles, its volume will be reduced by a half, and vice versa. The law was discovered in 1662 by Irish physicist and chemist (Robert Boyle.



		C



		catalyst substance that alters the speed of, or makes possible, a chemical or biochemical reaction but remains unchanged at the end of the reaction. Enzymes are natural biochemical catalysts. In practice most catalysts are used to speed up reactions.



		cathode negative electrode of an electrolytic cell, toward which positive particles (cations), usually in solution, are attracted.



		cation ion carrying a positive charge. During electrolysis, cations in the electrolyte move toward the cathode (negative electrode).



		cell, electrical, or voltaic cell or galvanic cell, device in which chemical energy is converted into electrical energy; the popular name is "battery," but this actually refers to a collection of cells in one unit. The reactive chemicals of a primary cell cannot be replenished, whereas secondary cells—such as storage batteries—are rechargeable: their chemical reactions can be reversed and the original condition restored by applying an electric current. It is dangerous to attempt to recharge a primary cell.



		chain reaction succession of reactions, usually involving free radicals, where the products of one stage are the reactants of the next. A chain reaction is characterized by the continual generation of reactive substances.



		Charles's law law stating that the volume of a given mass of gas at constant pressure is directly proportional to its absolute temperature (temperature in kelvin). It was discovered by French physicist Jacques Charles in 1787, and independently by French chemist Joseph Gay-Lussac in 1802.



		chromatography technique for separating or analyzing a mixture of gases, liquids, or dissolved substances. This is brought about by means of two immiscible substances, one of which (the mobile phase) transports the sample mixture through the other (the stationary phase). The mobile phase may be a gas or a liquid; the stationary phase may be a liquid or a solid, and may be in a column, on paper, or in a thin layer on a glass or plastic support. The components of the mixture are absorbed or impeded by the stationary phase to different extents and therefore become separated. The technique is used for both qualitative and quantitive analyses in biology and chemistry.



		combustion burning, defined in chemical terms as the rapid combination of a substance with oxygen, accompanied by the evolution of heat and usually light. A slow-burning candle flame and the explosion of a mixture of gasoline vapor and air are extreme examples of combustion. Combustion is an exothermic reaction as heat energy is given out.



		compound chemical substance made up of two or more elements bonded together, so that they cannot be separated by physical means. Compounds are held together by ionic or covalent bonds.



		colloid substance composed of extremely small particles of one material (the dispersed phase) evenly and stably distributed in another material (the continuous phase). The size of the dispersed particles (1–1,000 nanometers across) is less than that of particles in suspension but greater than that of molecules in true solution.



		covalent bond chemical bond produced when two atoms share one or more pairs of electrons (usually each atom contributes an electron). The bond is often represented by a single line drawn between the two atoms. Covalently bonded substances include hydrogen (H₂), water (H₂O), and most organic substances.



		crystal substance with an orderly three-dimensional arrangement of its atoms or molecules, thereby creating an external surface of clearly defined smooth faces having characteristic angles between them. Examples are table salt and quartz.



		crystallography scientific study of crystals. In 1912 it was found that the shape and size of the repeating atomic patterns (unit cells) in a crystal could be determined by passing X-rays through a sample. This method, known as X-ray diffraction, opened up an entirely new way of "seeing" atoms. It has been found that many substances have a unit cell that exhibits all the symmetry of the whole crystal; in table salt (sodium chloride, NaCl), for instance, the unit cell is an exact cube.



		D



		dative bond covalent bond in which one atom supplies both bonding electrons.



		density measure of the compactness of a substance; it is equal to its mass per unit volume and is measured in kg per cubic meter/lb per cubic foot. Density is a scalar quantity. The average density D of a mass m occupying a volume V is given by the formula:



		Relative density is the ratio of the density of a substance to that of water at 4°C/32.2°F.



		diffusion spontaneous and random movement of molecules or particles in a fluid (gas or liquid) from a region in which

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		they are at a high concentration to a region of lower concentration, until a uniform concentration is achieved throughout. The difference in concentration between two such regions is called the concentration gradient. No mechanical mixing or stirring is involved. For instance, if a drop of ink is added to water, its molecules will diffuse until their color becomes evenly distributed throughout. Diffusion occurs more rapidly across a higher concentration gradient and at higher temperature.



		dilution process of reducing the concentration of a solution by the addition of a solvent.



		E



		electrode any terminal by which an electric current passes in or out of a conducting substance; for example, the anode or cathode in a battery or the carbons in an arc lamp. The terminals that emit and collect the flow of electrons in thermionic valves (electron tubes) are also called electrodes: for example, cathodes, plates, and grids.



		electron stable, negatively charged elementary particle; it is a constituent of all atoms, and a member of the class of particles known as leptons. The electrons in each atom surround the nucleus in groupings called shells; in a neutral atom the number of electrons is equal to the number of protons in the nucleus. This electron structure is responsible for the chemical properties of the atom (see atomic structure).



		element substance that cannot be split chemically into simpler substances. The atoms of a particular element all have the same number of protons in their nuclei (their atomic number).



		F



		fatty acid, or carboxylic acid, organic compound consisting of a hydrocarbon chain, up to 24 carbon atoms long, with a carboxyl group (–COOH) at one end. The covalent bonds between the carbon atoms may be single or double; where a double bond occurs the carbon atoms concerned carry one instead of two hydrogen atoms. Chains with only single bonds have all the hydrogen they can carry, so they are said to be saturated with hydrogen. Chains with one or more double bonds are said to be unsaturated. Fatty acids are produced in the small intestine when fat is digested.



		formula representation of a molecule, radical, or ion, in which the component chemical elements are represented by their symbols. An empirical formula indicates the simplest ratio of the elements in a compound, without indicating how many of them there are or how they are combined. A molecular formula gives the number of each type of element present in one molecule. A structural formula shows the relative positions of the atoms and the bonds between them. For example, for acetic acid, the empirical formula is CH₂O, the molecular formula is C₂H₄O₂, and the structural formula is CH₃COOH.



		free radical atom or molecule that has an unpaired electron and is therefore highly reactive. Most free radicals are very short-lived. They are byproducts of normal cell chemistry and rapidly oxidize other molecules they encounter. Free radicals are thought to do considerable damage to living organisms. They are neutralized by protective enzymes.



		functional group part of a molecule that actively takes part in the normal reactions of that molecule.



		G



		gamma radiation high-energy electromagnetic radiation emitted by some nucleides in the course of radioactive decay.



		gas form of matter, such as air, in which the molecules move randomly in otherwise empty space, filling any size or shape of container into which the gas is put.



		gel solid produced by the formation of a three-dimensional cage structure, commonly of linked large-molecular-mass polymers, in which a liquid is trapped. It is a form of colloid. A gel may be a jellylike mass (pectin, gelatin) or have a more rigid structure (silica gel).



		H



		half-life during radioactive decay, the time in which the strength of a radioactive source decays to half its original value. In theory, the decay process is never complete and there is always some residual radioactivity. For this reason, the halflife of a radioactive isotope is measured, rather than the total decay time. It may vary from millionths of a second to billions of years.



		halogen any of a group of five nonmetallic elements with similar chemical bonding properties: fluorine, chlorine, bromine, iodine, and astatine. They form a linked group in the periodic table of the elements, descending from fluorine, the most reactive, to astatine, the least reactive. They combine directly with most metals to form salts, such as common salt (NaCl). Each halogen has seven electrons in its valence shell, which accounts for the chemical similarities displayed by the group.



		hydrocarbon any of a class of chemical compounds containing only hydrogen and carbon (for example, the alkanes and alkenes). Hydrocarbons are obtained industrially principally from petroleum and coal tar.



		I



		inert gas, or noble gas, any of a group of six elements (helium, neon, argon, krypton, xenon, and radon), so named because they were originally thought not to enter into any chemical reactions. This is now known to be incorrect: in 1962, xenon was made to combine with fluorine, and since then, compounds of argon, krypton, and radon with fluorine and/or oxygen have been described.



		ion atom, or group of atoms, that is either positively charged (cation) or negatively charged (anion), as a result of the loss or gain of electrons during chemical reactions or exposure to certain forms of radiation. In solution or in the molten state, ionic compounds such as salts, acids, alkalis, and metal oxides conduct electricity. These compounds are known as electrolytes.



		ionic bond, or electrovalent bond, bond produced when atoms of one element donate electrons to atoms of another element, forming positively and negatively charged ions, respectively. The attraction between the oppositely charged ions constitutes the bond. Sodium chloride (Na⁺Cl^–) is a typical ionic compound.



		isomer chemical compound having the same molecular composition and mass as another, but with different physical or chemical properties owing to the different structural arrangement of its constituent atoms. For example, the organic compounds butane (CH₃(CH₂) ₂CH₃) and methyl propane (CH₃CH(CH₃) CH₃) are isomers, each possessing four carbon atoms and ten hydrogen atoms but differing in the way that these are arranged with respect to each other.

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		isotope one of two or more atoms that have the same atomic number (same number of protons), but which contain a different number of neutrons, thus differing in their atomic mass (see atomic weight). They may be stable or radioactive, naturally occurring or synthesized. For example, hydrogen has the isotopes ²H (deuterium) and ³H (tritium). The term was coined by English chemist Frederick Soddy, pioneer researcher in atomic disintegration.



		L



		lanthanide any of a series of 15 metallic elements (also known as rare earths) with atomic numbers 57 (lanthanum) to 71 (lutetium).



		One of its members, promethium, is radioactive. All occur in nature. Lanthanides are grouped because of their chemical similarities (most are trivalent, but some can be divalent or tetravalent), their properties differing only slightly with atomic number.



		liquid state of matter between a solid and a gas. A liquid forms a level surface and assumes the shape of its container. Its atoms do not occupy fixed positions as in a crystalline solid, nor do they have freedom of movement as in a gas. Unlike a gas, a liquid is difficult to compress since pressure applied at one point is equally transmitted throughout (Pascal's principle). Hydraulics makes use of this property.



		lone pair pair of electrons in the outermost shell of an atom that are not used in bonding. In certain circumstances, they will allow the atom to bond with atoms, ions, or molecules (such as boron trifluoride, BF₃) that are deficient in electrons, forming coordinate covalent (dative) bonds in which they provide both of the bonding electrons.



		M



		metallic bond force of attraction operating in a metal that holds the atoms together. In the metal the valence electrons are able to move within the crystal and these electrons are said to be delocalized. Their movement creates short-lived, positively charged ions. The electrostatic attraction between the delocalized electrons and the ceaselessly forming ions constitutes the metallic bond.



		molecule molecules are the smallest particles of an element or compound that can exist independently. Hydrogen atoms, at room temperature, do not exist independently. They are bonded in pairs to form hydrogen molecules. A molecule of a compound consists of two or more different atoms bonded together. Molecules vary in size and complexity from the hydrogen molecule (H₂) to the large macromolecules of proteins. They may be held together by ionic bonds, in which the atoms gain or lose electrons to form ions, or by covalent bonds, where electrons from each atom are shared in a new molecular orbital.



		monomer chemical compound composed of simple molecules from which polymers can be made. Under certain conditions the simple molecules (of the monomer) join together (polymerize) to form a very long chain molecule (macromolecule) called a polymer. For example, the polymerization of ethene (ethylene) monomers produces the polymer polyethene (polyethylene).



		N



		neutralization process occurring when the excess acid (or excess base) in a substance is reacted with added base (or added acid) so that the resulting substance is neither acidic nor basic.



		nonmetal one of a set of elements (around 20 in total) with certain physical and chemical properties opposite to those of metals. Nonmetals accept electrons and are sometimes called electronegative elements.



		nucleon in particle physics, either a proton or a neutron, when present in the atomic nucleus.



		nucleus positively charged central part of an atom, which constitutes almost all its mass. Except for hydrogen nuclei, which have only protons, nuclei are composed of both protons and neutrons. Surrounding the nuclei are electrons, of equal and opposite charge to that of the protons, thus giving the atom a neutral charge.



		O



		orbital area of space around an atom or molecule where an electron is likely to be found.



		oxidation loss of electrons, gain of oxygen, or loss of hydrogen by an atom, ion, or molecule during a chemical reaction.



		oxide compound of oxygen and another element, frequently produced by burning the element or a compound of it in air or oxygen.



		P



		peptide molecule comprising two or more amino acid molecules (not necessarily different) joined by peptide bonds, whereby the acid group of one acid is linked to the amino group of the other (–CO.NH). The number of amino acid molecules in the peptide is indicated by referring to it as a di-, tri-, or polypeptide (two, three, or many amino acids).



		periodic table of the elements table in which the elements are arranged in order of their atomic number. The table summarizes the major properties of the elements and enables predictions to be made about their behavior.



		pH scale from 0 to 14 for measuring acidity or alkalinity. A pH of 7.0 indicates neutrality, below 7 is acid, while above 7 is alkaline. Strong acids, such as those used in car batteries, have a pH of about 2; strong alkalis such as sodium hydroxide are pH 13.



		plastic any of the stable synthetic materials that are fluid at some stage in their manufacture, when they can be shaped, and that later set to rigid or semirigid solids. Plastics today are chiefly derived from petroleum. Most are polymers, made up of long chains of identical molecules.



		polymer compound made up of a large long-chain or branching matrix composed of many repeated simple units (monomers) linked together by polymerization. There are many polymers, both natural (cellulose, chitin, lignin) and synthetic (polyethylene and nylon, types of plastic). Synthetic polymers belong to two groups: thermosoftening and thermosetting.



		polysaccharide long-chain carbohydrate made up of hundreds or thousands of linked simple sugars (monosaccharides) such as glucose and closely related molecules.



		precipitation formation of an insoluble solid in a liquid as a result of a reaction within the liquid between two or more soluble substances. If the solid settles, it forms a precipitate; if the particles of solid are very small, they will remain in suspension, forming a colloidal precipitate (see colloid).

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		R



		radical group of atoms forming part of a molecule, which acts as a unit and takes part in chemical reactions without disintegration, yet often cannot exist alone for any length of time; for example, the methyl radical –CH₃, or the carboxyl radical –COOH.



		radioactive decay process of disintegration undergone by the nuclei of radioactive elements, such as radium and various isotopes of uranium and the transuranic elements. This changes the element's atomic number, thus transmuting one element into another, and is accompanied by the emission of radiation. Alpha and beta decay are the most common forms.



		radioactivity spontaneous alteration of the nuclei of radioactive atoms, accompanied by the emission of radiation. It is the property exhibited by the radioactive isotopes of stable elements and all isotopes of radioactive elements, and can be either natural or induced. See radioactive decay.



		reaction coming together of two or more atoms, ions, or molecules with the result that a chemical change takes place; that is, a change that occurs when two or more substances interact with each other, resulting in the production of different substances with different chemical compositions. The nature of the reaction is portrayed by a chemical equation.



		reduction gain of electrons, loss of oxygen, or gain of hydrogen by an atom, ion, or molecule during a chemical reaction.



		S



		salt any compound formed from an acid and a base through the replacement of all or part of the hydrogen in the acid by a metal or electropositive radical. Common salt is sodium chloride.



		semiconductor material with electrical conductivity intermediate between metals and insulators and used in a wide range of electronic devices. Certain crystalline materials, most notably silicon and germanium, have a small number of free electrons that have escaped from the bonds between the atoms. The atoms from which they have escaped possess vacancies, called holes, which are similarly able to move from atom to atom and can be regarded as positive charges. Current can be carried by both electrons (negative carriers) and holes (positive carriers). Such materials are known as intrinsic semiconductors.



		soap mixture of the sodium salts of various fatty acids: palmitic, stearic, and oleic acid. It is made by the action of sodium hydroxide (caustic soda) or potassium hydroxide (caustic potash) on fats of animal or vegetable origin. Soap makes grease and dirt disperse in water in a similar manner to a detergent.



		solid state of matter that holds its own shape (as opposed to a liquid, which takes up the shape of its container, or a gas, which totally fills its container). According to kinetic theory, the atoms or molecules in a solid are not free to move but merely vibrate about fixed positions, such as those in crystal lattices.



		solution two or more substances mixed to form a single, homogenous phase. One of the substances is the solvent and the others (solutes) are said to be dissolved in it.



		solvent substance, usually a liquid, that will dissolve another substance. Although the commonest solvent is water, in popular use the term refers to low-boiling-point organic liquids, which are harmful if used in a confined space. They can give rise to respiratory problems, liver damage, and neurological complaints.



		spectroscopy study of spectra associated with atoms or molecules in solid, liquid, or gaseous phase. Spectroscopy can be used to identify unknown compounds and is an invaluable tool in science, medicine, and industry (for example, in checking the purity of drugs).



		standard temperature and pressure, STP standard set of conditions for experimental measurements, to enable comparisons to be made between sets of results. Standard temperature is 0°C/32°F (273K) and standard pressure 1 atmosphere (101,325 Pa).



		sublimation conversion of a solid to vapor without passing through the liquid phase.



		substitution reaction replacement of one atom or functional group in an organic molecule by another.



		suspension mixture consisting of small solid particles dispersed in a liquid or gas, which will settle on standing. An example is milk of magnesia, which is a suspension of magnesium hydroxide in water.



		T



		trace element chemical element necessary in minute quantities for the health of a plant or animal. For example, magnesium, which occurs in chlorophyll, is essential to photosynthesis, and iodine is needed by the thyroid gland of mammals for making hormones that control growth and body chemistry.



		transition metal metal with an unfilled inner electron shell. Such elements are good conductors of heat and electricity and in their compounds can have variable valence. An example is copper, which in its compounds can have a charge of +1 or +2. The compounds of transition elements are usually colored.



		V



		valence measure of an element's ability to combine with other elements, expressed as the number of atoms of hydrogen (or any other standard univalent element) capable of uniting with (or replacing) its atoms. The number of electrons in the outermost shell of the atom dictates the combining ability of an element.



		volatile term describing a substance that readily passes from the liquid to the vapor phase. Volatile substances have a high vapor pressure.

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		Further Reading



		Adloff, Jean P. (ed.) Handbook of Hot Atom Chemistry (1992)



		Alexander, W. and Street, A. Metals in the Service of Man (1972)



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