Empirical rules for interpreting atomic spectra used to determine the lowest energy level for a configuration of two equivalent electrons (i.e. electrons with the same n and l quantum numbers) in a many-electron atom. (1) The lowest energy state has the maximum multiplicity consistent with the Pauli exclusion principle. (2) The lowest energy state has the maximum total electron orbital angular momentum quantum number, consistent with rule (1). These rules were put forward by the German physicist Friedrich Hund (1896–1993) in 1925. Hund's rules are explained by quantum theory involving the repulsion between two electrons.
Subjects: Chemistry — Physics.