Sommerfeld–Kossel displacement law

The shift theorem of Sommerfeld and Kossel, named after Arnold Sommerfeld and Walther Kossel, describes spectra of hydrogenlike atoms. It comes to similar energy levels between successive positively charged atoms. Sommerfeld and Kossel formulated this as follows:

" The spectrum of any atom is very similar to the spectrum of the single- pos. charged atom that follows in the periodic table. "

Example:

So it comes with roughly equal energy levels of about 13.6 eV for hydrogen with a principal quantum number, for He and Li2 with.