Question

Explain the reactivity of group 16 elements towards halogens.

Answer 1

1. The group 16 elements with halogens form a large number of halides of the type EX₂, EX₄ and EX₆ where E is an element of the group and X is a halogen.

2. The stability of the halides decreases in the order fluoride > chloride > bromide > iodide.

3. The hexahalides SF₆, SeF₆, TeF₆ are formed by direct combination. They are colourless gases. The hexahalides have sp³d² hybridisation and have an octahedral structure. SF₆ is exceptionally stable due to steric reasons.

4. The tetrahalides SF₄, SeF₄, TeF₄, TeCl₄ have sp³d hybridisation and thus have a trigonal bipyramidal structure in which one of the equatorial positions is occupied by a lone pair of electrons. This geometry is also called see-saw geometry.

5. The dihalides SCl₂, SeCl₂, TeCl₂ have sp³ and thus have a tetrahedral structures with two equatorial positions occupied by lone pairs.

6. The monohalides S₂F₂, S₂Cl₂, Se₂Cl₂ and Se₂Br₂ are dimeric in nature. These halides have a tendency to undergo disproportionation. 

For example,

2Se₂Cl₂ → SeCl₄ + 3Se