The lour valence electron of the alkali metals first element

The lour valence electron of the alkali metals (first element in each row of the periodic table) is well described by hydrogen is wave function. Consider the 3p excited state of the sodium valence electron. Is this level split by the spin-orbit interaction, and if yes, into how many levels?

Solution

Yes. This level (3p) is split by spin orbit interaction. 3p level split into two levels (3p_1/2 and 3p_3/2). These levels are called sodium duoblets.