Explain the following observations giving an appropriate reason for each.
(i) The enthalpies of atomization of transition elements are quite high.
(ii) There occurs much more frequent metal-metal bonding in compounds of heavy transition metals (i.e., 3rd series).
(iii) Mn2+ is much more resistant than Fe2+ towards oxidation.
(i) Because of large number of unpaired electrons in their atoms, the transition metals have strong interatomic interactions and hence stronger bonding between atoms, resulting in higher enthalpies of atomization.
(ii) In the same group of d-block elements, the 4d and 5d transition elements are larger in size than than those of 3d elements. Hence, the valence electrons are less tightly held and form metal–metal bond more frequently.
(iii) Mn3+(d 4 ) is less stable than Mn2+ (d 5 , half filled) while Fe3+ (d 5 , half filled) is more stable than Fe2+ (d 4 ). That is why Mn2+ is more resistance than Fe2+ towards oxidation.