Compare the chemistry of actinoids with that of lanthanoids with special reference to 

(i) Electronic configuration

(ii) oxidation state

(iii) atomic and ionic sizes 

(i) Electronic configuration. The general electronic configuration of lanthanoids is [Xe]⁵⁴ 4f^1–14 5d^0–1 6s² whereas that of actinoids is [Rn]⁸⁶ 5f^1–14 6d^0–1 7s². Thus, lanthanoids belong to 4f-series whereas actinoids belong to 5f-series.

(ii) Oxidation states. Lanthanoids show limited oxidation states (+2, +3, +4) out of which +3 is most common. This is because of large energy gap between 4 f and 5d subshells. On the other hand, actinoids show a large number of oxidation states because of small energy gap between 5f, 6d and 7s subshells.

(iii)  Atomic and ionic sizes. Both show decrease in size of their atoms or ions in + 3 oxidation state. In lanthanoids, the decrease is called lanthanoid contraction whereas in actinoids, it is called actinoid contraction. However, the contraction is greater from element to element in actionoids due to poorer shielding by 5f electrons than that by 4f electrons in lanthanoids.