Question

The extent of actinoid contraction is greater than lanthanoid contraction. Explain Why?

Answer 1

• The electronic configurations of : Lanthanoids [Xe] 4f^1-14 5d^0-1 6s² Actinoids [Rn] 5f^1-14, 6d^0-1 7s²
• The mutual screening offered in case of 5f-electrons is less than that in the 4f-electrons.
• Hence, the outer orbitals are pulled to the greater extent by nuclei in actinoids (5f-series) than in lanthanoids (4f-series).
• Therefore, actinoid contraction is greater than lanthanoid contraction.