In
chemistry, a
valence electron is an
electron that is associated with an
atom, and that can participate in the formation of a
chemical bond; in a single
covalent bond, both atoms in the bond contribute one valence electron in order to form a
shared pair. The presence of valence electrons can determine the element's chemical properties and whether it may bond with other elements: For a
main group element, a valence electron can only be in the outermost
electron shell. In a
transition metal, a valence electron can also be in an inner shell.