An unpaired electron is an electron occupying an orbital on its own, without a partner of opposite spin. Unpaired electrons give an atom or ion a net magnetic moment, making it paramagnetic. Their number can often be predicted from the electron configuration using Hund's rule.

未成对电子是单独占据一个轨道、没有相反自旋伙伴的电子。未成对电子使原子或离子具有净磁矩,从而呈顺磁性。其数目常可用洪特规则由电子排布预测。