Answer the following questions:
i) Which element in the first series of transition elements does not exhibit variable oxidation states, and why?
ii) Why do actinoids, in general, exhibit a greater range of oxidation states than the lanthanoids?
i) Which element in the first series of transition elements does not exhibit variable oxidation states, and why?
ii) Why do actinoids, in general, exhibit a greater range of oxidation states than the lanthanoids?
Solution
(i) Scandium (Z = 21, 3d4s) shows only the +3 state: removing all three valence electrons gives the very stable noble-gas core [Ar], and no other state offers comparable stability.
(ii) In the actinoids the 5f, 6d and 7s orbitals lie extremely close in energy, so electrons from all three can participate in bonding — giving states from +3 up to +7 (e.g. U: +3→+6, Np: +3→+7). In the lanthanoids the 4f electrons are buried and essentially only +3 appears.
(ii) In the actinoids the 5f, 6d and 7s orbitals lie extremely close in energy, so electrons from all three can participate in bonding — giving states from +3 up to +7 (e.g. U: +3→+6, Np: +3→+7). In the lanthanoids the 4f electrons are buried and essentially only +3 appears.
CBSE Class 12 Board · 2007 · Foreign · Subjective