Choose the element with the highest first ionization energy.

Hint: recall that there are some discontinuities in the trend of IE values in the periodic table.

A.

Na

B.

Mg

C.

Al

D.

K

E.

Ca

Hello

This question requires an understanding of the general trend of ionization energies. The first ionization energy increases from left to right in the periodic table due to increase in the number of valence shell electrons. Therefore, we will narrow our choices down to B, C, and E. As we move up the periodic table, the ionization energy increases due to smaller size, thus greater attraction. Therefore we are left with Mg and Al as options.

Now, we must look into the orbitals of each atom.

The aluminium atom's valence shell has 3 electrons, 2 paired and one unpaired electron. On the other hand, Mg's 2 valence electrons are present in the form of a pair. The paired configuration has higher energy so Mg's first ionization energy is higher.