Compare the chemistry of actinoids with that of the langthanoids with special reference to :
(a) electronic configuration
(ii) oxidation state
(iii) atomic and ionic sizes, and
(d) chemical reactivity.

Explanation

(a) Electronic configuration : The general electronic configuration of langthnoids is `[Xe]4f^(1-14)5d^(0-1)6s^(2)` whereas that of actinoids is `[Rn]5f^(1-14)6d^(0-1)7s^(2)`. Thus, lanthanoids belong to 4f-series whereas actinoids belong to 5f-series.
(b) Oxidation state : Lanthanoids show limited oxidation states `(+2,+3,+4)` out of which +3 is most common. This is because of large energy gap between 4f, 5d and 6s subshells. On the other hand, actinoids show a large number of oxidation states because of small energy gap between 5f, 6d and 7s subshells.
(c) Atomic and ionic sizes : Both lanthanoids and actinoids 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 actinoids due to poorer shielding by 5f electrons.
(d) Chemical reactivity : Important reactions of lanthanoids and actinoids are given below :
Lanthanoids :
(i) They combine with `H_(2)` on gentle heating with carbon, then form carbides. When burnt in presence of halogen, they form halides.
(ii) They react with dilute acids to liberate hydrogen gas.
(iii) They form oxides and hydroxides of the type `M_(2)O_(3)` and `M(OH)_(3)` which are basic in character.
Actinoids :
(i) They combine with most of the non-metals at moderate temperature with carbon, they form carbide, with sulphur, sulphides are formed and with halogens, halides are formed.
(ii) These metals are attacked by hydrochloric acid, but the effect of nitric acid is small due to the formation of boilling water to give a mixture of oxides and hydroxides.
(iv) Alkalis have no action on them.