d-block contraction

The elements in question are gallium, germanium, arsenic, selenium, bromine, and krypton[citation needed].

The d-block contraction is best illustrated by comparing some properties of the group 13 elements to highlight the effect on gallium.

The most obvious effect is that the sum of the first three ionization potentials of gallium is higher than that of aluminium, whereas the trend in the group would be for it to be lower.

The second table below shows the trend in the sum of the first three ionization potentials for the elements B, Al, Sc, Y, and La.

The outer valence electrons are more strongly attracted by the nucleus causing the observed increase in ionization potentials.

Atomic radius of elements of the groups 2 , 13 and 14 , showing the "d-block contraction" , especially for Ga and Ge