Question

Account for the following.
(i) Zr and Hf have almost similar atomic radii.
(ii) Transition metals show variable oxidation states.
(iii) Cu⁺ ion is unstable in aqueous solution.

Answer 1

(i)The variable oxidation states of transition elements are due to the participation of ns and (n−1)d-electrons in bonding. Lower oxidation state is exhibited when ns- electrons take part in bonding. Higher oxidation states are exhibited when (n − 1) d-electrons take part in bonding.

(ii)This is because the atomic radii of 4d and 5d transition elements are nearly same. This similarity in size is consequence of lanthanide contraction. Because of this lanthanide contraction the radii of Hf becomes nearly equal to that of Zr.

(iii)Transition elements act as good catalyst in chemical reaction because they can lend electrons or withdraw electrons from the reagent, depending on the nature of the reaction. The ability of transition metals to be in a variety of oxidation states, the ability to interchange between the oxidation states and the ability to form complexes with the reagents and be a good source for electrons make transition metals good catalysts.