Which of the following factor may be regarded as the main cause of lanthanide contraction?

Options

A. Poor shielding of one of the `4f-` electrons by anoher in the sub-shell.
B. Effective shielding of one of the `4f-`electrons by another in the sub-shell
C. Poorer shielding of 5d electron by 4f electrons.
D. Greater shielding of 5d electron by 4f electron.

Answer

1

Explanation

This phenomenon is associated with the intervention of the `4f` orbitals which must be filled before the `5d` seried of elements begin. The filling of `4f` before `5d` orbital results in a regular decrease in atomic radii called Lanthanoid contraction. This is because of poor shielding of one of the `4f-` electrons by another in the subshell.