- Of the different multiplets resulting from different configurations of electrons in @[email protected] of an atom those with greatest multiplicity have the lowest energy (multiplicity rule).
- Among multiplets having the same multiplicity, the lowest-energy one is that with the largest total orbital @[email protected] (@[email protected] rule) (valid if the total orbital @[email protected] is a constant of motion).
- In configurations containing shells less than half full of electrons, the term having the lowest total @[email protected] \(J\) lies lowest in energy, whereas in those with shells more than half filled, the term having the largest value of \(J\) lies lowest (fine structure rule). Hund rules apply if the 'Russell–Saunders' @[email protected] scheme is valid. Sometimes the first rule is applied with questionable validity to molecules.