Compare the chemistry of actinoids with that of the lanthanoids with special reference to: (i) electronic configuration (ii) atomic and ionic sizes and (iii) oxidation state (iv) chemical reactivity.

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Solution

(i) Electronic configuration
lanthanoids have general electronic configuration $[X e] 4 f^{1 - 14} 5 d^{0 - 1} 6 s^{2}$ . Actinoids have general electronic configuration $[R n] 5 f^{1 - 14} 6 d^{0 - 1} 7 s^{2}$ .
In lanthanoids, 4f orbital is filled and in actinoids, 5f orbital is filled.
(ii) Atomic and ionic sizes
The atomic and ionic sizes of lanthanoids and actinoids decrease with increase in the atomic number due to lanthanoid and actinoid contraction.
(iii) Oxidation state
Apart from +3 oxidation state, lanthanoids show +2 and +4 oxidation states due to large energy gap between 4f and 5d subshells. Whereas actinoids show large number of oxidation states due to small energy gap between 5f and 6d subshells.
(iv) Chemical reactivity
Highly electropositive lanthanoids have almost similar chemical reactivity. Actinoids (electropostive and highly reactive) are more reactive (specially in finely divided state) than lanthanoids.

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Q. (i) With reference to structural variability and chemical reactivity, write the difference between lanthanoids and actinoids.
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+ 4

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M n O_{4}^{-} + 8 H^{+} + 5 e^{-} \to

(iv) Out of

{M n}^{3 +}

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Q. Assertion :The chemistry of the early actinoids is more complicated than the corresponding lanthanoids. Reason: Outer electronic configuration of actinoids is

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