a) Complete the following chemical reaction equations:
i) MnO₄⁻(aq) + C₂O₄²⁻(aq) + H⁺(aq) →
ii) Cr₂O₇²⁻(aq) + Fe²⁺(aq) + H⁺(aq) →
b) Explain the following observations about the transition/inner-transition elements:
i) There is in general an increase in the density of elements from titanium (Z = 22) to copper (Z = 29).
ii) There occurs much more frequent metal–metal bonding in compounds of the heavy transition elements (3rd series).
iii) The members of the actinoid series exhibit a larger number of oxidation states than the corresponding members of the lanthanoid series.
i) MnO₄⁻(aq) + C₂O₄²⁻(aq) + H⁺(aq) →
ii) Cr₂O₇²⁻(aq) + Fe²⁺(aq) + H⁺(aq) →
b) Explain the following observations about the transition/inner-transition elements:
i) There is in general an increase in the density of elements from titanium (Z = 22) to copper (Z = 29).
ii) There occurs much more frequent metal–metal bonding in compounds of the heavy transition elements (3rd series).
iii) The members of the actinoid series exhibit a larger number of oxidation states than the corresponding members of the lanthanoid series.
Solution
(a)(i)
(ii)
(b)(i) From Ti to Cu the atomic mass increases while the radius stays nearly constant (d-electron shielding balances nuclear charge); density = mass/volume therefore rises steadily.
(ii) The heavier (5d) metals have large, diffuse d-orbitals that overlap strongly between neighbouring atoms (reflected in their very high enthalpies of atomisation), so direct metal–metal bonds and cluster compounds (e.g. of W, Re, Os) are common.
(iii) Actinoid 5f, 6d and 7s orbitals are nearly degenerate, letting varying numbers of electrons bond — states +3 to +7; buried lanthanoid 4f electrons restrict lanthanoids to essentially +3.
(ii)
(b)(i) From Ti to Cu the atomic mass increases while the radius stays nearly constant (d-electron shielding balances nuclear charge); density = mass/volume therefore rises steadily.
(ii) The heavier (5d) metals have large, diffuse d-orbitals that overlap strongly between neighbouring atoms (reflected in their very high enthalpies of atomisation), so direct metal–metal bonds and cluster compounds (e.g. of W, Re, Os) are common.
(iii) Actinoid 5f, 6d and 7s orbitals are nearly degenerate, letting varying numbers of electrons bond — states +3 to +7; buried lanthanoid 4f electrons restrict lanthanoids to essentially +3.
CBSE Class 12 Board · 2009 · Delhi · Subjective