How do successive ionization energies of aluminum, and magnesium compare?
Well consider the electronic structure of aluminum versus magnesium.........Data are from here.
Now the electron removed that is first removed from aluminum is a p-orbital based electron. This has zero electron density at the nucleus, even though there is a greater nuclear charge. We would expect a priori that the p electron is easier to remove than an s electron, which of course, is the valence electron for magnesium. And thus the ionization energies reflect the electronic structure of the atom.
Why are the third ionization energy for