Explain anomalous behaviour of oxygen with respect to atomicity, magnetic property and oxidation state.

Answer: Oxygen differs from the other group 16 elements because of its small size, high electronegativity and the absence of d orbitals in its valence shell.

1. Atomicity: Because of its small size, oxygen forms strong pπ–pπ double bonds, so it exists as a discrete diatomic molecule O₂ (a gas). Sulphur and the other members do not form stable pπ–pπ bonds; they form single bonds with each other and exist as polyatomic molecules such as S₈ (solids).
2. Magnetic property: O₂ has two unpaired electrons (in antibonding π* orbitals) and is paramagnetic, whereas S₈ and the other elements are diamagnetic.
3. Oxidation state: Oxygen generally shows −2 (also −1 in peroxides, −½ in superoxides, and +1, +2 only with fluorine, as in O₂F₂, OF₂). Having no d orbitals it cannot expand its octet and cannot show +4 or +6, which S, Se and Te show.