Question

How will you explain the lower atomic radius of gallium as compare to aluminium?

Answer 1

But, although gallium lies next to aluminium in the group, gallium is smaller then aluminum because galliam electrons occupy 3D sub shell hence resulting in reduction of affective nuclear charge. This happens because of the difference in attraction forces of electrons on nucleus. This is also called shielding affect.

Answer 2

Answer:

Gallium has one more shell in it than aluminium. Thus, Ga is expected to be of higher atomic radius than Al. However, in reality it is not so. This is because Ga has 3 d electrons, which has poor shielding effect. So, the effective nuclear charge on the outermost electrons is higher than Al, as a result of which the atomic radii decreases and is lower than Al.