Question

Explain:
(i) Transition elements mostly form the complex compound. Why?
(ii) Transition elements are good catalyst. Why?
(iii) Transition elements show variable valency. Why?

Answer 1

(i) Tendency of transition element to form complexes compound is due to (1) Variable valency and different oxidation states. (2) Small size of transition elementions and high nuclear charge. (3) Availability of vacant d orbitals to accommodate lone pair of electrons donated by lingonds.
(ii) Transitional elements act as good catalysts in chemical reaction. In the hydrogenation Ni metal, In contact process of manufacture of SO, Pt and in manufacture of NH${}_3$ by Haber process Fe acts as catalyst. In the method of preparation O${}_2$ by heating KClO${}_3$, MnO${}_2$ acts as catalyst.
(iii) Transition metals exhibit variable valencies because the energy subshell (n - 1)d and ns are very close. Thus, possibility to lose electrons from ns subshell as well as from (n - 1)d subshell is very much if there an unpaired electrons. So oxidation states of these metals may increase.
In these elements Mn shows maximum variable valencies.