Question

From element to element, the actinoid contraction is greater than the lanthanoid contraction due to poor shielding by 5f-electrons in actinoids than that by 4f-electrons in the lanthanoids.

• A. True
• B. False

Answer 1

The correct option is A True

Lanthanoid Contraction

1. The steady decrease in the atomic and ionic radii of the transition metals as the atomic number increases.
2. This is because the filling of $4\mathrm{f}$ orbitals before the $5\mathrm{d}$ orbitals are called lanthanoid contraction.
3. This is due to the imperfect shielding of one $4\mathrm{f}$ electron by another in the same subshell.

Actinoid Contraction

1. The gradual decrease in the ionic radii with the increase in atomic number is called actinoid contraction.
2. It is due to the imperfect shielding of one $5\mathrm{f}$ electrons by another in the same subshell.
3. Along with the series, the nuclear charge and number of $5\mathrm{f}$ electrons increase by one unit.
4. However, due to imperfect shielding of $5\mathrm{f}$ orbitals, which results in the contraction of the size.

Therefore, due to poor shielding of $5\mathrm{f}$ electrons actinoid contraction is more than lanthanoid contraction, the above statement is true.