Question

Discuss briefly the properties of group 16 elements.

Answer 1

1. Elements: Group 16 includes oxygen (O), sulphur (S), selenium (Se), tellurium (Te), and polonium (Po).
2. Atomic and Physical Properties: Atomic radius and density increase down the group. Melting and boiling points increase down the group, except polonium, which shows lower values due to the inert pair effect. Oxygen is diatomic (O₂), while sulphur exists mainly as S₈ molecules.
3. Ionisation Energy: High ionisation energies decrease down the group. Lighter elements have slightly lower ionisation energy than the corresponding Group 15 elements due to the stability of half-filled p orbitals in Group 15.
4. Electronegativity: Group 16 elements have higher electronegativity than Group 15. Oxygen is the second most electronegative element. Electronegativity decreases from oxygen to polonium.
5. Electron Gain Enthalpy: Values are high, but oxygen has less negative electron gain enthalpy than sulphur due to small atomic size. Electron gain enthalpy decreases down the group.
6. Oxidation States: The common oxidation state is −2. Oxygen also shows +2 in OF₂ and −1 in peroxides. The tendency to show -2 oxidation decreases down the group.
7. Allotropy: All elements show allotropy. Oxygen has ozone (O₃) as an allotrope.
8. Hydrides: Form hydrides of type H₂M with angular structures. Hydride bond angles and thermal stability decrease down the group. Acidic strength of hydrides increases down the group.
9. Metallic Character: Increases down the group from non-metallic oxygen to metallic polonium.