valence science definition

A whole number that represents the ability of an atom or a group of atoms to combine with other atoms or groups of atoms. The valence is determined by the number of electrons that an atom can lose, add, or share. An atom's valence is positive if its own electrons are used in forming the bond, or negative if another atom's electrons are used. For example, a carbon atom can share four of its electrons with other atoms and therefore has a valence of +4. A sodium atom can receive an electron from another atom and therefore has a valence of -1. (In this book the distinction between positive and negative valences is ignored unless it is relevant.) The valence of an atom generally indicates how many chemical bonds it is capable of forming with other atoms. Also called valence number, oxidation state.