Para os mais curiosos...
A regra de Madelung explica, por exemplo , porque a orbital 4s tem menor energia que a 3d na distribuição e permite-nos escrever as configurações electrónicas segundo o diagrama de Pauling.Mas alguns elementos de transição não seguem esta regra (é o caso do urânio)
Electron shells filled in violation of Madelung's rule (red)
Uranium 92 [Rn] 7s2 5f3 6d1
There are several more exceptions to Madelung's rule among the heavier elements, and it is more and more difficult to resort to simple explanations such as the stability of half-filled subshells. It is possible to predict most of the exceptions by Hartree–Fock calculations, which are an approximate method for taking account of the effect of the other electrons on orbital energies. For the heavier elements, it is also necessary to take account of the effects of Special Relativity on the energies of the atomic orbitals, as the inner-shell electrons are moving at speeds approaching the speed of light.