Definition of: valence

(vā′ləns) noun Chem.
1. The property possessed by an element or radical of combining with or replacing other elements or radicals in definite and constant proportion.
2. The number of atoms of hydrogen (or its equivalent), taken as unity, with which an atom or radical can combine, or which it can replace. It varies with different elements, and with certain elements in different compounds.
3. Med. The combining power of certain substances or bodies, as serums, chromosomes, and the like. Also va′len·cy. [<LL valentia strength, orig. neut. plural of L valens, -entis, ppr. of valere be well, be strong]