Describe the general characteristics of transition elements with special reference to the following:
(i) catalytic behaviour.
(ii). Complex formation,
(iii) intersitital compounds.

Explanation

(i) The transition metals form reaction intermediates due to the presence of vacant orbitals or their tendency to form variable oxidaiton state. These intermediates give reaction paths of lower activation energy and, thereofre, increase the rate of the reaction. these reaction intermediates readily decompose yielding the products and regenerating the original substance.
(ii) the transition elements form a large number of coordination complexes. The transition metal ions bind to a number of anions or neutral molecules in these complexes. the great tendency of transition metal ions to form complexes is due to (i) small size of the atoms and ions. (ii) high nuclear charge and (iii) availability of vacant d-orbitals of suitable energy to accept lone pairs of electrons donated by ligands.
(iii) Transition metals form interstitial compounds with elements such as hydrogen, boron, carbon and nitrogen. the small atoms of these non-metallic elements (H,B,C,N etc.) get trapped in vacant spaces of the lattices of the transition metal atoms.
As a result of the fi lling up of the interstitial spaces. the transition metals become rigid and hard. these interstitial compounds have similar chemical properties as the paraent metals but differ significantly in their physical properties particularly, density, hardness and conductivity.