The decrease in atomic and ionic radii from actinium to lawrencium is greater than the corresponding

Question

The decrease in atomic and ionic radii from actinium to lawrencium is greater than the corresponding contraction in the lanthanoids. What is the primary reason for this?

Professor PC Thomas Classes · Answer

The actinoid contraction is greater because the 5f electrons provide even poorer shielding from the increasing nuclear charge than the 4f electrons in lanthanoids, leading to a stronger inward pull on the valence shell.