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Group 16 (O, S, Se, Te, Po) has ns^{2np}^4. Oxygen is anomalous: small size, high EN, no d-orbitals (max covalence = 2), forms H-bonds, only shows -2 and -1 states.

Sulphur chemistry is rich: S8 rhombic allotrope (most stable at RT), variable oxidation states (-2, +2, +4, +6). SO2 is bent, acts as reducing and oxidising agent, bleaches temporarily by reduction. H2SO4 (Contact process: S to SO2 to SO3 via V2O5 to oleum to H2SO4) is a strong acid, dehydrating agent, and oxidising agent when hot concentrated.

SF6 exists (S has d-orbitals, sp3d2, octahedral) but OF6 does not (O lacks d-orbitals). SF6 is kinetically inert (steric protection by 6 F atoms).

H2O2 has open-book structure, O in -1 state, acts as both oxidiser and reducer. Oxygen forms peroxides ($O2^{2-}$, bond order 1) and superoxides ($O2^-$, bond order 1.5, paramagnetic). Larger alkali metals favour superoxides.

Thermal stability of hydrides decreases down the group: H2O >> H2S > H2Se > H2Te. Reducing character increases inversely. Boiling points: H2O anomalously high (H-bonding), then H2Te > H2Se > H2S.