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HYDRATE

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Originally appearing in Volume V14, Page 35 of the 1911 Encyclopedia Britannica.
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HYDRATE , in See also:

chemistry, a See also:compound containing the elements of See also:water in See also:combination; more specifically, a compound containing the monovalent hydroxyl or OH See also:group. The first and more See also:general See also:definition includes substances containing water of See also:crystallization; such salts are said to be hydrated, and when deprived of their water to be dehydrated or anhydrous. Compounds embraced by the second definition are more usually termed hydroxides, since at one See also:time they were regarded as combinations of an See also:oxide with water, for example, See also:calcium oxide or See also:lime when slaked with water yielded calcium hydroxide, written formerly as CaO•See also:H2O. The general formulae of hydroxides are: Mi OH, Mii(OH)2, Mili(OH)3, M1v(OH)4, &c., corresponding to the oxides M21O, M110, M2iiiO3, MivO2, &c., the See also:Roman See also:index denoting the See also:valency of the See also:element. There is an important difference between non-metallic and metallic hydroxides; the former are invariably acids (oxyacids), the latter are more usually basic, although acidic metallic oxides yield acidic hydroxides. Elements exhibiting strong basigenic or oxygenic characters yield the most_ See also:stable hydroxides; in other words, stable hydroxides are associated with elements belonging to the extreme See also:groups of the periodic See also:system, and unstable hydroxides with the central members. The most stable basic hydroxides are those of the See also:alkali metals, viz. See also:lithium, See also:sodium, See also:potassium, See also:rubidium and See also:caesium, and of the alkaline See also:earth metals, viz. calcium, See also:barium and See also:strontium; the most stable acidic hydroxides are those of the elements placed in groups VB, VIB and VIIB of the periodic table.

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