oxidation
Oxides As with the halides, the nature of bonding in oxides of the transition elements is determined by the oxidation state of the metal. Oxides with low oxidation states tend to be more ionic, whereas those with higher oxidation states are more covalent. These variations in bonding are because the electronegativities of the elements are not fixed values. The electronegativity of an element increases with increasing oxidation state. Transition metals in low oxidation states have lower electronegativity values than oxygen; therefore, these metal oxides are ionic. Transition metals in very high oxidation states have electronegativity values close to that of oxygen, which leads to these oxides being covalent. The oxides of the first transition series can be prepared by heating the metals in air. These oxides are Sc2O3, TiO2, V2O5, Cr2O3, Mn3O4, Fe3O4, Co3O4, NiO, and CuO. Alternatively, these oxides and other oxides with the metals in different oxidation states can be produced by heating the corresponding hydroxides, carbonates, or oxalates in an inert atmosphere. Iron II oxide can be prepared by heating iron II oxalate, and cobalt II oxide is produced by heating cobalt II hydroxide:.