Transition Elements: Oxidation States

Oxidation state of an element is defined as the degree of oxidation (loss of electron) of the element in achemical compound. Transition elements exhibit a wide variety of oxidation states in their compounds. For example: manganese shows all the oxidation states from +2 to +7 in its compounds. However, some elements exhibit few oxidation states, for example: Sc, Zn. The lower oxidation states exhibited by these elements is attributed to the fact that either they have few electrons to lose, for example Sc or too many d electrons (hence, fewer orbitals to share electron with others) for higher valence for example Zn. The variable oxidation states of transition elements arise mainly out of incomplete filling of d orbitals in such a way that their oxidation states differ from each other by unity.

Oxidation States - Transition Elements

Transition elements oxidation states


Stability of oxidation states

Higher oxidation states are shown by chromium, manganese and cobalt. In case of halides, manganese doesn’t exhibit +7 oxidation state, however MnO3F is known.Cu+2 (aq) is known to be more stable than Cu+ (aq) as the  ΔhydH of Cu+2 is more than Cu+, which compensates for the second ionisation enthalpy of Cu. Mn exhibits high oxidation states in the oxides, for example:inMn2O7the oxidation state of Mn is +7. As oxygen is able to form multiple bonds with metal, Mn oxide, Mn2O7 shows a higher oxidation states in comparison to Mn fluorides, MnF4.In Mn2O7, each Mn is tetrahedrally surrounded by O’s including a Mn-O-Mn bridge. However, other elements of the group exhibit +3 oxidation states such as Fe2O3 and +4 oxidation state such as V2O4. In p-block elements we have seen lower oxidation states are favoured by the heavier members (due to inert pair effect) whereas, we acknowledge an opposite trend in d-block. As in group 6, Mo (VI) is found to have higher stability in comparison to Cr (VI).

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