@Kotov

My suggestion is that pl understand the spectra of Alkali atoms from any text book on

Atomic and Molecular spectra . After that apply your problem. Spectra nature can be 

understood directly from Symbol but requires some  practice/ detail analysis.

Prof B.Rath

Thank you for your answer. So it is not possible to sum up some values to get the relation between the levels? For instance in basic chemistry course to remember which level is higher which is lower(for example 6s and 4f) we used such rule: s=0, p=1, d=2, f=3. And E(6s)=6+0=6, E(4f)=4+3=7. So 4f is higher then 6s.