Question

Describe the properties of O, S, Se, Te and Po (group 16 elements) with reference to allotropy.

Answer 1

1. All elements exhibit allotropy, existing in different structural forms.
2. Oxygen has two allotropes: dioxygen (O₂, more stable) and ozone (O₃).
3. Sulphur shows several allotropes: mainly orthorhombic S_n (most stable), polymeric chain forms (catena-S_n), and small unstable molecules (S₂ to S₅).
4. Selenium has six allotropes; common ones include red monoclinic Se₈ rings and grey hexagonal spiral chain forms.
5. Tellurium exists in metallic and nonmetallic allotropes.
6. Polonium has two metallic allotropes, α and β forms.
7. The tendency for catenation and multiple bond formation decreases down the group.
8. Oxygen forms strong double bonds (pπ–pπ), which decrease from S to Po.
9. Metallic character increases down the group; oxygen and sulphur are non-metallic, Se and Te are semiconductors, and Po is metallic.