Question

(a) How would you account for the following:
(i) Actinoid contraction is greater than lanthaniod contraction.
(ii) Transition metals form coloured compounds.
(b) Complete the following equation:
$2Mn{O}_4^{-}+6H^{+}+5N{O}_2^{-}\to$

Answer 1

(a) (i) The 5f orbitals (in case of actinoids) have a poorer shielding effect than 4f orbitals (in lanthanoids). Thus, the effective nuclear charge experienced by electron in valence shells in case of actinoids is greater than that in lanthaniods.

(ii) In the presence of ligands, the d-orbitals of transition metal ions split up into two sets of orbitals having different energies Thus, the transition of electrons takes place from one set to another. The energy required for those transitions is quite less and falls in the visible regions of radiation. The ions of transition metals absorb the radiation of a particular wavelength and the rest is reflected, impacting colour to the solution

b) $2Mn{O}_4^{-}+6H^{+}+5N{O}_2^{-}\to 2M{n}^{2+}+5N{O}_3^{-}+3H_{2}O$