The Wiswesser rule gives a simple method to determine the energetic sequence of the atomic subshells (n,l). n is the principal quantum number and l is the azimuthal quantum number. The energetic sequence of the subshells characterized by the quantum numbers (n,l) is the sequence that leads to a monotonous increasing row of function values for the Wiswesser-function.
W(n,l)=n + l - ( l /(l+1) )
For example: if n=2 and l=1, this correspondents with an 2p-orbital.
The results are : 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p,...
* Atomic orbital energy