Question

Which of the following factors may be regarded as the main cause of lanthanoid contraction?

Options

• Greater shielding of 5d electrons by 4f electrons.

• Poorer shielding of 5d electrons by 4f electrons.

• Effective shielding of one of 4f electrons by another in the subshell.

• Poor shielding of one of 4f electrons by another in the subshell.

Answer 1

Poorer shielding of 5d electrons by 4f electrons.

Explanation:

Lanthanides have poorer shielding of 5d electrons by 4f electrons, resulting in greater nucleus attraction over 5d electrons and contraction of the atomic radii.