Discuss the physical properties of group-16 elements.

Explanation

(i) Atomicity : Oxygen is diatomic gas while other elements are polyatomic solid. Example : Sulphur, selenium and tellurium exists as polyatomic molecule such as `S_8`, `Se_8` etc. This is due to tendency of oxygen to form pn-pn bonds due to its small size and high bond enthalpy of (O = O) bond.
(ii) Metallic character : Down the group, the metallic character of the elements increases. Oxygen and sulphur are non-metals, selenium and tellurium are metalloids where as polonium is a metal. Polonium is radioactive. The half life period is 13.8 days.
(iii) Melting points and boiling points : The melting points and boiling points gradually increases down the group. The large difference between melting and boiling points of oxygen and sulphur is due to atomicity. Oxygen is diatomic where as sulphur is polyatomic.
(iv) Allotropy : All the elements of group-10 shows allotropy.