Describe Variable Oxidation states of D-Block Elements

All transition elements exhibit variety of oxidation states (or) variable valencies in their compounds. This property is due to the following reasons.

i) These elements have several (n – 1) d and ns electrons.

ii) The energies of (n – 1)d and ns orbitals are fairly close to each other.


Features of oxidation states of transition elements

  1. The elements which exhibit the maximum number of oxidation states occur either in or near the middle of the series. For example , in the first transition series manganese exhibits maximum number of oxidation states (+2 to +7).
  2. The elements in the beginning of the series exhibit fewer oxidation states because they have less number of d-electrons which they can lose or contribute for sharing. The elements at the end of the series exhibit fewer oxidation states, because they have too many d electrons and hence fewer vacant d-orbitals can be involved in bonding.
  3. The transition elements in lower oxidation states (+2 and +3) generally form ionic bonds and in higher oxidation state form covalent bonds.
  4. The highest oxidation state shown by any transition metal is +8. For example, ruthenium and osmium show highest oxidation states of +8 in some of their compounds.
  5. Some transition metals show oxidation state of zero in their compounds. Ni(CO)4 and Fe(CO)5 are common examples.