Question

How would you account for the following?
(i) Transition metals exhibit variable oxidation states
(ii) $Zr(Z=40)$ and $Hf(Z=72)$ have almost identical radii
(iii) Transition metals and their compounds act as catalyst.

Answer 1

(i) The variable oxidation states of transition elements are due to the participation of $ns$ and $(n-1)d-$ electron in bonding. Lower oxidation state is exhibited when $ns-$electron 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 reagents, depending on the nature of the reaction. The ability of transition metals to be in a variety of ooxidation states, the ability of interchange between he oxidation states and the ability to form complexes with the reagent and be a god source for electrons make transition metals good catalysts.