The elements of first transition series from variety of oxides of different oxidation states having general formulae MO, M2O3, M3O6, MO2, MO3. These oxides are generally formed by heating the metal with oxygen at high temperature. These oxides are listed in the table below:
TiO (b), TiO2 (b), TiO2 (c)
VO (b), V2O3 (b), VO2 (c), V2O5 (a)
CrO (b), Cr2O3 (c), CrO2 (c), Cr2O3 (a)
MnO (b), Mn2O3 (b), Mn3O4 (c), MnO2 (c), Mn2O7 (a)
FeO (b), Fe2O3 (c), Fe3O4 (b)
Cu2O (b), CuO (c)
All the metals except scandium form MO oxides which are ionic in nature. The highest oxidation number of the metal in the oxides coincides with the group number is attained in case of metals from scandium to manganese (Sc2O3 to Mn2O7). Beyond group-7, no higher oxides except Fe2O3 are known. Besides the oxides, the oxocations stabilize V(V) as VO2+, V(IV) as VO2+ and Ti(IV) as TiO2+.These oxides exhibit acidic, basic and amphoteric behaviour.Some of the characteristic features of these oxides are given below:(i) In general, oxides are basic when the metal is in lower oxidation state and they are acidic if the metal is in higher oxidation state.(ii) The oxides are generally amphoteric if the metal is in intermediate oxidation state.