(i) Electronic configuration. The general electronic configuration of langthanoids is `[Xe]^(54) 4f^(1-14) 5d^(0-1) 6s^(2)` whereas that of actinoids is `[Rn]^(86) 5f^(1-14) 6 s^(0-1) 7s^(2)` . Thus, langthanoids belong to 4f- series whereas actinoids belong to 5f - series.
(ii) Oxidation staes. Lnathanoids show limited oxidation states`( + 2, +3, +4)` out of which `+3` is most common. This is becasue of large energy gap between 4 f and 5d subshells. On the other hand, actinoids show a large number of oxidation staes becasue of small energy gap between 5f , 6d and 7s subshell.
(iii) Atomic and ionic sizes. Both show decrease in size of their atoms or ions in `+3` oxidation state. In langthanoids, the decrease is called langthanoid contraction whereas in actinoids, it is called actinoid contraction . However , the contraction is greater from element to element in actinoids due to poorer shielding by 5f electrons than that by 4f electrons in langthanoids.
(iv) Chemical reactivity. Refer to page.
