(a) Account for the following :
(i) Transition metals show variable oxidation states.
(ii) Zn, Cd and Hg are soft metals.
(iii) E0 value for the Mn3+/Mn2+ couple is highly
positive (+ 1·57 V) as compared to Cr3+/Cr2+
(b) Write one similarity and one difference between the chemistry of lanthanoid and actinoid elements.

 

 

 

 
 
 
 
 

Answers (1)
S Sumit

(a) (i) Transiction metals show variable oxidation state due to presence of valence electrons in two different sets of orbitals ie outer ns and (n-1)d. Both of them can get involved in bond formation due to small difference of energy between them.
(ii) Zn, Cd, Hg are soft metals as they have break metalic bonds in their lattices due to absence of unpaired d electrons.
(iii) E0(Mn3+/Mn2+) is highly positive as compared to Cr3+/Cr2+, it shows that Mn2+ has the 3d5 configuration which is extra stable half filled configuration
(b) Similarity - Both lanthanoids and actinoids form coloured ions due to presence of unpaired f electrons and f-f transition
 Difference - Ionisation enthalpy of lanthanoids are grater than those of actinoids because 4f orbitals are more penetrating than 5f.

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