Core electrons are the inner-shell electrons of an atom, lying close to the nucleus below the valence shell. They take little part in chemical bonding but provide the most significant shielding of the valence electrons from the nuclear charge. They contrast with valence electrons, which occupy the outermost shell and determine chemical behaviour.

内层电子是原子的内壳层电子,位于价层之下、靠近原子核。它们很少参与化学成键,却对价电子相对于核电荷提供最主要的屏蔽。它们与占据最外层、决定化学性质的价电子相对。