Why would it take more energy to take 2 electrons from an atom of sodium than it does t take 3 electrons from an atom of aluminum?

1 Answer
Apr 16, 2016

Consider the valence shell of sodium versus aluminum.


#"Aluminum, Z = 13"#, with an electronic configuration of #1s^(2)2s^(2)2p^(6)3s^(2)3p^1#, versus #"Natrium, Z = 11":# #1s^(2)2s^(2)2p^(6)3s^(1)# .

The second electron removed from the sodium atom is removed from an inner non-valence shell, which is closer to the nucleus, and thus more tightly held. It makes sense that this electron should require more energy to remove. On the other hand, aluminum has three valence electrons, with #n=3#. The fourth ionization enthalpy of aluminum should be disproportionately high.