Glossary
valence electron
Valence electrons are the electrons in an atom's outermost shell; they decide bonding and the element's group.
Valence electrons are the electrons in the outermost shell of an atom — the ones available for bonding. They are the electrons that an atom gains, loses or shares to form ions and chemical bonds, so they decide an element's chemistry far more than the inner electrons do. Their number is read from the periodic table: in the main-group elements, atoms in the same group (a vertical column) have the same number of valence electrons, which is why a column behaves alike. A group-1 metal has one valence electron and tends to lose it, and a group-17 nonmetal has seven and tends to gain one. Atoms are most stable with a full outer shell, so an element's drive to reach that count explains the bonds it forms and the formula of the compound it makes.
Taught in
Related terms
- periodic table — The periodic table arranges the elements by atomic number so that columns (groups) share chemical behavior.
- ion — An ion is an atom (or group) with a charge, made by losing or gaining electrons; a metal loses, a nonmetal gains.
- atom — An atom is the smallest unit of an element, built from a nucleus of protons and neutrons with electrons around it.
Source: OpenStax Chemistry 1e and Chemistry: Atoms First 1e, first editions (CC BY 4.0). Each definition restates the Chemistry guide in this exam, which carries the per-source citations on its own page. (OpenStax 1e accessed 2026-10-08)