valence (n.) Look up valence at Dictionary.com
early 15c., "extract, preparation," from Latin valentia "strength, capacity," from valentem (nominative valens) "strong, stout, vigorous, powerful," present participle of valere "be strong" (see valiant). Meaning "relative combining capacity of an element" is recorded from 1884, from German Valenz (1868), from the Latin word. Related: Valency.