Describe The general characteristics of transition elements with special reference to the following:
Catalyst

Answer

(i) The transition metals reaction intermediatews due to the presence of vacant orbitals or their tendency to form variable oxidation states. These intermediates give reaction paths of lower activation energy and, thereofe, increase the rate of the reaction intermediates readily decompose yielding the products and regenerated the original substance.
(ii) The transition elements form a large number of coordination complexes. The transition metal ions bind to a number of anlons or neutral mole cules 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 (iiii) availability of vacant d-orbitals of suitable enrgy to accept lone pairs of electrons donated by ligands.
(iii) Transition metals form interstital compounds with elementws 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 filling up of the interstital spaces, the transition metals become rigid and har. Thee intersitital compounds have similar chemical properties as the parent metals but differ significantly in their physical properties particulary, density, hardness and conductivity.