A valence electron is an electron in the valence shell, the outermost occupied shell of an atom. Valence electrons are primarily responsible for an element's chemical behaviour, since they are the electrons involved in forming bonds. The number of valence electrons is what gives elements in the same group their similar properties.

价电子是处于价层(原子最外层被占据的壳层)中的电子。价电子主要决定元素的化学性质,因为它们是参与成键的电子。价电子的数目正是使同一族元素性质相似的原因。