The valence shell is the outermost occupied electron shell of an atom. The electrons it contains, the valence electrons, are the ones most readily involved in bonding, so the valence shell largely determines an element's chemical behaviour. Atoms tend to gain, lose, or share electrons so as to achieve a stable valence shell, often an octet.

价层是原子最外层被占据的电子壳层。它所含的电子(即价电子)是最易参与成键的电子,因此价层在很大程度上决定元素的化学性质。原子倾向于通过得失或共享电子来获得稳定的价层,通常是八电子组态。