Binding energy of 2p electron in Lithium

[Gregg]

Homework Statement

Explain why the 2p state for Lithium is close to the n=2 state for Hydrogen and why the 2s state is much higher. (5.4eV)

The Attempt at a Solution

I think that for 2p state (n=2, l=1) we can model (for some reason) the Lithium valence electron like the electron orbiting Hydrogen. My guess is that we cannot do this for the l=0 state (2s) but I am unsure why this is the case.

 

[Gregg]

Could it be that because the electron has angular momentum that it is less influenced by the other electrons in the n=1 state and we can treat the 2 electron 3 proton system as 1 proton?