valence electron

[noun]

Electrons that can be actively involved in chemical change; usually electrons in the shell with the highest value of n (electrons in the "outermost" shell of an atom). For example, sodium's ground state electron configuration is 1s² 2s² 2p⁶ 3s¹; the 3s electron is the only valence electron in the atom. Valence electrons determine the chemical properties of an atom and are the only electrons that participate in chemical bonding.