valence , valency (va´lens, -len-se)
The combining power of one atom of an element (or a radical), that of the hydrogen atom being the unit of comparison, determined by the number of electrons in the outer shell of the atom (v. electrons); e.g., in HCl, chlorine is monovalent; in H2O, oxygen is bivalent; in NH3, nitrogen is trivalent. [L. valentia, strength]
negative v. the number of v. electrons an atom can take up.
positive v. the number of v. electrons an atom can give up.
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