Why the atomic radius of Gallium is less than that of aluminium?

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answered Jan 31, 2022 by Princebarnwal (32.6k points)
selected Feb 1, 2022 by Jeewant

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Atomic radius of the elements increases down the group due to addition of new shells.
Electronic configuration of Al is [Ne]3s² 3p¹ while that of Ga is [Ar]3d¹⁰ 4s² 4p¹
As Al does not have d-electrons, it offers an exception to this trend.
As we go from Al down to Ga the nuclear charge increases by 18 units. Out of the 18 electrons added, 10 electrons are in the inner 3d subshell of Ga. These d-electrons offer poor shielding effect.
Therefore, the effect of attraction due to increased nuclear charge is experienced prominently by the outer electrons of Ga and thus, its atomic radius becomes smaller than that of Al.

Hence, the atomic radius of gallium is less than that of aluminium.