They assume Russell-Saunders coupling, though for heavier elements spin-orbit coupling becomes more important.
Their quantitative basis can be summarized by Racah parameters, which represent electron-electron repulsions. They assume Russell-Saunders coupling, though for heavier elements spin-orbit coupling becomes more important. Two of them consider the total angular momentum and orbital angular momentum of an atom. As a result of another one of them, singlet states are generally found to be more unstable than triplet states. FTP identify this set of rules for determining the lowest energy electron configuration of an atom, one of which states that the lowest energy state of an atom will have electrons in different orbitals with parallel spins.
Their quantitative basis can be summarized by Racah parameters, which represent electron-electron repulsions.
{Hund}’s rules