Question

How would you explain the lower atomic radius of gallium as compared element?

Answer 1

It is due to poor shielding of the valence elrctrons of Ga by inner 3D electrons.As a result effective nuclear charge of gallium is somewhat greater in magnitude than that of any other compared element (suppose aluminium), does electron in gallium experiences the greater force of attraction by nucleus then in compared element.Hence the atomic size of Gallium (135pm) is slightly less.

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