State reasons for the following:
i) Cu(+1) ion is not stable in aqueous solution.
ii) Unlike Cr³⁺, Mn²⁺, Fe³⁺ and the subsequent other M²⁺ ions of the 3d series, the 4d and 5d series metals generally do not form stable cationic species.
i) Cu(+1) ion is not stable in aqueous solution.
ii) Unlike Cr³⁺, Mn²⁺, Fe³⁺ and the subsequent other M²⁺ ions of the 3d series, the 4d and 5d series metals generally do not form stable cationic species.
Solution
(i) In water Cu disproportionates:
The very large (negative) hydration enthalpy of the small, doubly charged Cu more than compensates the second ionisation enthalpy of copper, so Cu(+1) is unstable in aqueous solution.
(ii) The 4d and 5d metals have much higher ionisation enthalpies (and enthalpies of atomisation) than their 3d congeners; the energy cost of forming simple cations is not recovered by hydration. They therefore prefer higher oxidation states with covalent bonding or complex/cluster species rather than stable simple cations.
The very large (negative) hydration enthalpy of the small, doubly charged Cu more than compensates the second ionisation enthalpy of copper, so Cu(+1) is unstable in aqueous solution.
(ii) The 4d and 5d metals have much higher ionisation enthalpies (and enthalpies of atomisation) than their 3d congeners; the energy cost of forming simple cations is not recovered by hydration. They therefore prefer higher oxidation states with covalent bonding or complex/cluster species rather than stable simple cations.
CBSE Class 12 Board · 2011 · All India · Subjective