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

Nov 23, 2016

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.

$M g ,$ $Z = 12$: $1 {s}^{2} 2 {s}^{2} 2 {p}^{6} 3 {s}^{2}$.

$A l ,$ $Z = 13$: $1 {s}^{2} 2 {s}^{2} 2 {p}^{6} 3 {s}^{2} 3 {p}^{1}$

Because the third ionization energy involves the removal of a $2 p$ 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 $A {l}^{3 +}$ 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.