Actinoid contraction is greater than lanthanoid contraction:
i. The size of the atoms or ions of actinoids decrease regularly along the series with the increase in atomic number from actinium to lawrencium. This steady decrease in the ionic radii with the increase in atomic number is called actinoid contraction.
ii. The actinoid contraction is due to the imperfect shielding of 5f-electron.
Despite of the imperfect shielding of 5f-orbitals, the effective nuclear charge increases which results in contraction of the size.
iii. It may be noted that in actinoid contraction, there are bigger jumps in ionic size between the consecutive members as compared to lanthanoids.
iv. This is due to lesser shielding of 5f-electrons (as compared to shielding of 4f-electrons in lanthanoids) which results in greater increase in the effective nuclear charge and therefore, larger attraction.
