The quantum number j detects the whole magnetic and whole mechanical moments of some atom: Mj= gj(j(j+1))1/2 and j=(j(j+1))1/2, where gj-Lande factor. Quantum number j may be calculate by using Hund's rule, if you know the other quantum numbers S and L of electronic core of atom consisting not a whole numbers of electrons.

thank you Ms Olga Dyogteva .