Reactivity towards halogens

i. Group 16 elements : Elements of group 16 react with halogens to give a large number of halides of the types $\mathrm{EX_6}$, $\mathrm{EX_4}$ and $\mathrm{EX_2}$ (where E = S, Se, Te).

Hexahalides — $\mathrm{SF_6}$, $\mathrm{SeF_6}$ and $\mathrm{TeF_6}$ — are formed by direct combination. They are colourless gases. They have $\mathrm{sp^3d^2}$ hybridisation and possess octahedral structure. $\mathrm{SF_6}$ is an exceptionally stable halide, for steric reasons. The stability of the halides decreases in the order fluorides > chlorides > bromides > iodides.

Tetrahalides — $\mathrm{SF_4}$, $\mathrm{SeF_4}$, $\mathrm{TeF_4}$ and $\mathrm{TeCl_4}$ — have trigonal bipyramidal geometry with one equatorial position occupied by a lone pair, which corresponds to $\mathrm{sp^3d}$ hybridisation of the central atom.

Dihalides — $\mathrm{SCl_2}$, $\mathrm{SeCl_2}$ and $\mathrm{TeCl_2}$ — have $\mathrm{sp^3}$ hybridisation and thus possess tetrahedral structure, with two equatorial positions occupied by lone pairs.

Monohalides are dimeric in nature — for example $\mathrm{S_2F_2}$, $\mathrm{S_2Cl_2}$, $\mathrm{Se_2Cl_2}$ and $\mathrm{SeBr_2}$. These dimeric halides undergo disproportionation:

ii. Group 17 elements : Halogens (group 17 elements) combine amongst themselves to form a number of compounds known as interhalogen compounds. These are of the following types: $\mathrm{XX'}$, $\mathrm{XX'_3}$, $\mathrm{XX'_5}$, $\mathrm{XX'_7}$, where X is the halogen atom of larger size and X′ is the halogen atom of smaller size. More details of interhalogen compounds are included in section 7.12. …