Resumen de Hund's Multiplicity Rule Revisited.
The helium atom 1s12s1 excited state gives rise to singlet and triplet terms. The fact that the triplet state has a lower energy is frequently attributed to greater electron�electron repulsion in the singlet state. However, high-level quantum mechanical calculations show that the reason the triplet state is lower than the singlet is due to greater electron�nucleus attraction in the triplet state. The purpose of this article is to present a relatively simple quantum mechanical model for Hund's multiplicity rule that is accessible to undergraduate audiences and consistent with conclusions based on high-level quantum mechanical calculations.
