Question

Oxygen usually exists in −2 oxidation state but it exhibits +2 state in OF₂. Explain.

Answer 1

1. Group 16 elements have an electronic configuration of ns² np⁴ and want to gain 2 electrons to achieve a noble gas configuration, showing a −2 oxidation state.
2. The tendency to show −2 oxidation state decreases down the group because electronegativity decreases from oxygen to polonium.
3. Lower electronegativity means a weaker ability to attract electrons and form M²⁻ ions.
4. Thus, heavier elements like sulphur and polonium less readily form −2 ions; polonium does not show −2 oxidation state at all.

This is due to increasing atomic size and decreasing effective nuclear charge down the group.