234.

Describe the general characteristics of the transition elements with special reference to their tendency to:
(i)    Exhibit paramagnetism.
(ii)    Form complex compounds.
(iii)    Their catalytic behaviour.

(i)
Transition elements show paramagnetism. Paramagnetism is due to the presence of unpaired electrons in the d-orbitals of transition metal atoms, ions or molecules. The greater the number of unpaired electrons, the greater is the paramagnetism.

(ii)
Transition elements have strong tendency to form complex ion. This is because transition elements form small, highly charged ions, which have vacant (n – 1) d-orbitals of approximately the appropriate energy to accept lone pairs of electrons donated by other groups or molecules, such as cyanide ion, water and ammonia molecules.


(iii)
Most of the transition elements act as catalyst e.g., finely divided nickel is used in the hydrogenation of vegetable oils, iron in the manufacture of ammonia by Haber’s Process. This is because transition elements form transient intermediate complexes utilising empty d-orbitals. Consequently, low energy path-ways for slow reactions are provided which increase the rate of the reaction.