How much energy does it take to singly ionize a neutral lithium atom by removing an electron from the $1s$ orbital?
You can obtain this directly from the energy-levels part of the NIST Atomic Spectra Database.
Li Ifor the energy levels of neutral lithium, or
Li IIfor the energy levels of the first cation.
- Choose whatever
Level unitsyou're most comfortable with.
Retrieve Data to get the results.
The ionization energy you want is not listed explicitly, and you need to get it as the sum of two factors:
- The ionization energy from
Li II, which is listed in the spectrum of
Li I, at the entry Li II ($1s^2$ $^1S_0$) at the left-hand column.
- The excitation energy from the $1s^2$ of the cation to the relevant $1s\,2s$ of the cation, which are listed in the
Note that there are two such states, with a small $\sim 1\:\rm eV$ energy difference between them, depending on how the two remaining spins are aligned. (Though, frankly, given how ridiculously hard it is to excite the cation to anything other than the ground state, this difference may well be negligible.)