Question

Account for the following :

(i) In the 3d transition series, zinc has the lowest enthalpy of atomisation.

(ii) Cu⁺ ion is unstable in aqueous solution.

(iii) Actinoids show more number of oxidation states than lanthanoids.

Answer 1

(i) In 3d transition series, zinc has the lowest enthalpy of atomisation due to weak metallic bonding.

(ii) Cu⁺ is unstable in aqueous solution as it disproportionates to Cu²⁺ and Cu due to higher enthalpy of hydration of Cu²⁺.

\(2Cu^+ \rightarrow Cu^{2+} + Cu\) 

(iii) Actinoids show more number of oxidation states than lanthanoids because of the fact that 5f, 6d and 7s levels are of comparable energies.