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

1 Answer
Nov 30, 2015

Answer:

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?