Question

Discuss the anomalous behaviour of oxygen in relation to the properties of group 16 elements.

Answer 1

1. Selenium forms oxoacids similar to sulphur, mainly selenous acid (H₂SeO₃) and selenic acid (H₂SeO₄).
2. Selenous acid (H₂SeO₃) is formed by oxidation of selenium and contains selenium in +4 oxidation state.
3. Selenic acid (H₂SeO₄) contains selenium in +6 oxidation state and is a stronger acid than selenous acid.
4. The stability and acid strength of selenium oxoacids are less than those of corresponding sulphur oxoacids.
5. Selenium trioxide (SeO₃) forms cyclic tetrameric structures in the solid state.
6. Selenium oxoacids show decreasing stability going down group 16 from sulphur to tellurium.