Interchalcogen

The chalcogens react with each other to form interchalcogen compounds.

[1] Although no chalcogen is extremely electropositive,[note 1] nor quite as electronegative as the halogen fluorine (the most electronegative element), there is a large difference in electronegativity between the top (oxygen = 3.44 — the second most electronegative element after fluorine) and bottom (polonium = 2.0) of the group.

Combined with the fact that there is a significant trend towards increasing metallic behaviour while descending the group (oxygen is a gaseous nonmetal, while polonium is a silvery post-transition metal[note 2]), this causes the interchalcogens to display many different kinds of bonding: covalent, ionic, metallic, and semimetallic.

(Covalent bonding occurs when both elements have similar high electronegativities; ionic bonding occurs when the two elements have very different electronegativities, one low and the other high; metallic bonding occurs when both elements have similar low electronegativities.)

For example, in the leftmost column of the table (with bonds to oxygen), O2 and O3 are purely covalent, SO2 and SO3 are polar molecules, SeO2 forms chained polymers (stretching in one dimension), TeO2 forms layered polymers (stretching in two dimensions), and PoO2 is ionic with the fluorite structure (spatial polymers, stretching in three dimensions); in the bottom row of the table (with bonds to polonium), PoO2 and PoS are ionic, PoxSey and PoxTey are semimetallic, and Po∞ is metallic.

Molecular structure of sulfur monoxide .
Molecular structure of selenium trioxide .
Crystal structure of tellurium dioxide .
Unit cell of polonium dioxide ( cubic modification). Po: white; O: yellow.