Question

why there is a small increase in the atomic radii from si to pb??​

Answer 1

There is a small increase in the atomic radii from silicon to pb ( lead) because the atomic radii of the elements present in a group increases downwards

Answer 2

Answer:

because of the presence of completely filled d and f orbitals

Explanation:

Actually, the general trend of atomic size in a group is that atomic size increases as we move down the group. This is because as we move down the group, new shells are consecutively added.

The atomic size also depends on the inner shell electrons. Atomic size increases if filled sub-shell is present in inner shell. This effect is known as Shielding effect. The extent of shielding goes on decreasing as s>p>d>f. So, in heavy metals like Ge,Sn,Pb of group 14, due to presence of completely filled inner d-subshell ( as well as f-subshell in case of Pb), due to poor shielding effect of inner subshell, the nucleus has tight hold on valence shell. So there is only marginal increase in their atomic size.