Chem. [f. ATOMIC + -ITY.] The combining capacity of an element (or radical), i.e., the number of atoms of hydrogen, or other monovalent element, with which one of its atoms normally combines.
Thus the atomicity of chlorine is 1 (or chlorine is a monad) because it forms with hydrogen H Cl; and that of carbon is 4 (or carbon is a tetrad) because it forms with hydrogen C H4. Atomicity has also been called equivalence, quantivalence, adicity, and (now usually) valency.
1865. Reader, 1 April, 372. The word atomicity has been invented for the purpose of describing those properties of atoms which were described by the word ‘equivalence.’
1873. Cooke, Chem., 284. The number of these replaceable atoms measures what is called the atomicity of the compound.
