Question

Why is the first ionization energy of aluminum lower than the first ionization of magnesium?

Answer 1

Consider the nucleus-electron attraction for a `s` orbital electron versus a `p` orbital electron.

Explanation:

Electronic configuration of atomic `Mg`: `1s^(2)2s^(2)2p^(6)3s^2`, versus `Al`, `1s^(2)2s^(2)2p^(6)3s^(2)3p^1`.

Would you expect it to be easier to remove an electron from a `p` orbital (with zero electron density at the nucleus), versus an `s` orbital, which has density at the nucleus? Why?