Write a note on oxides and oxoanions of transition elements.

The ability of oxygen to stabilize the high oxidation states of metal than fluorine is higher because it forms a multiple bonds with a metal.

The metal oxides in lower oxidation state of metals are basic while that in highest oxidation state are acidic. The metal oxides having metals in intermediate oxidation states are amphoteric.

Ex. : $\mathrm{Mn}_{2} \mathrm{O}_{7}$ is acidic, $\mathrm{MnO}$ is basic while $\mathrm{Mn}_{3} \mathrm{O}_{4}, \mathrm{Mn}_{2} \mathrm{O}_{3}$ and $\mathrm{MnO}_{2}$ are amphoteric. Similary $\mathrm{CrO}$ is basic but $\mathrm{Cr}_{2} \mathrm{O}_{3}$ is amphoteric.

The oxides are generally formed by the reaction of metals with oxygen at high temperatures. Scandium forms only one oxide $\mathrm{Sc}_{2} \mathrm{O}_{3}$ in which it is highest oxidation state of $(+3)$. The oxidation state conincides with group number. This is observed till manganese Ex. : $\mathrm{Mn}_{2} \mathrm{O}_{7}$. Beyond manganese except iron no other elements forms oxide of type $\mathrm{M}_{2} \mathrm{O}_{3} . \mathrm{Ex} .: \mathrm{Fe}_{2} \mathrm{O}_{3}$.

Although ferrates $\left(\mathrm{FeO}_{4}^{2-}\right)$ are formed in alkali medium, they readily decompose to give $\mathrm{Fe}_{2} \mathrm{O}_{3}$ and $\mathrm{O}_{2}$. Besides the oxides, the oxocations stabilizes $\mathrm{V}^{+5}$ as $\mathrm{VO}_{2}^{+}, \mathrm{V}^{4+}$ as $\mathrm{VO}^{2+}$ and $\mathrm{Ti}^{4+}$ as $\mathrm{TiO}^{2+} . \mathrm{V}_{2} \mathrm{O}_{5}$ is however, amphoteric though mainly acidic and it gives $\mathrm{VO}_{4}^{3-}$ as well as $\mathrm{VO}^{2+}$ salts. In vanadium there is gradual change from the basic $\mathrm{V}_{2} \mathrm{O}_{3}$ to less basic $\mathrm{V}_{2} \mathrm{O}_{4}$ to amphoteric $\mathrm{V}_{2} \mathrm{O}_{5} . \mathrm{V}_{2} \mathrm{O}_{4}$ dissolves in acid to give $\mathrm{VO}^{2+}$ salts while $\mathrm{V}_{2} \mathrm{O}_{5}$ when dissolved in alkali gives $\mathrm{VO}_{4}^{3-}$ and in acids give $\mathrm{VO}_{4}^{+}$ respectively.

Oxides with metal in low oxidation states has ability to get oxidized and hence are basic while oxides with high oxidation states has tendency to get reduced in low oxidation state and hence are acidic in nature. The ionic character of metal oxides decrease with the increase in oxidation number of a metal. Ex. : $\mathrm{Mn}_{2} \mathrm{O}_{7}$ is a covalent green oil while $\mathrm{CrO}_{3}$ and $\mathrm{V}_{2} \mathrm{O}_{3}$ have low melting