Question

Which metal will have the highest third ionization energy, magnesium or aluminum?

Answer 1

On the basis of its electronic structure, clearly magnesium metal will have the highest third ionization energy.

Explanation:

Consider the electronic configurations of aluminum, and magnesium.

`Mg,` `Z=12`: `1s^(2)2s^(2)2p^(6)3s^(2)`.

`Al,` `Z=13`: `1s^(2)2s^(2)2p^(6)3s^(2)3p^1`

Because the third ionization energy involves the removal of a `2p` electron, that is more closely bound to the nuclear core, this electron should require more energy to remove. On the other hand, aluminum has 3 valence electrons, and a stable `Al^(3+)` oxidation state, from which only electrons from the third valence shell have been removed.

Now as a chemist, as a physical scientist, you should consult the data in order to establish that I am not telling pork pies. See [here for a start.](https://en.wikipedia.org/wiki/Ionization_energies_of_the_elements_%28data_page%29)