Oxides and Oxoanions of Metals

Oxides and Oxoanions of Metals

• Metals, except scandium, form MO oxides, which are ionic, through reaction with oxygen at high temperatures.
• The highest oxidation number in the oxides coincides with the group number and is attained in Sc₂O₃ to Mn₂O₇.
• Beyond group 7, no higher oxides of iron above Fe₂O₃ are known.

Properties of Higher Oxides

• As the oxidation number of a metal increases, its ionic character decreases.
• Higher oxides, such as Mn₂O₇, CrO₃, and V₂O₅, have low melting points.
• These higher oxides exhibit acidic character, with Mn₂O₇ giving HMnO₄, and CrO₃ giving H₂CrO₄ and H₂Cr₂O₇.
• V₂O₅ is amphoteric, giving VO₄³⁻ and VO₂⁺ salts.

Vanadium Oxides

• V₂O₃ is basic, while V₂O₄ is less basic, and V₂O₅ is amphoteric.
• V₂O₄ dissolves in acids to give VO²⁺ salts.
• V₂O₅ reacts with alkalies to give VO₄³⁻ and with acids to give VO₂⁺ ions.

Chromium Oxides

• CrO is basic, while Cr₂O₃ is amphoteric.
• Potassium dichromate (K₂Cr₂O₇) is a significant chemical used in the leather industry and as an oxidant for preparing azo compounds.