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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.^{[note 3][1]}

Known binary interchalcogens

Bonding in the binary interchalcogens

Going down the above table, there is a transition from covalent bonding (with discrete molecules) to ionic bonding; going across the table, there is a transition from ionic bonding to metallic bonding. (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, Po_xSe_y and Po_xTe_y are semimetallic, and Po_∞ is metallic.^[1]

Summary of known binary interchalcogens

Sulfur chalcogenides

Molecular structure of sulfur monoxide.

• 
  Lower sulfur oxides, S_xO_y where the ratio X:Y is greater than 1:2
  
  • 
    Disulfur monoxide, S₂O
  
  
  • 
    Disulfur dioxide, S₂O₂
  
  
  • 
    Sulfur monoxide, SO
  
  


• 
  Sulfur dioxide, SO₂


• 
  Sulfur trioxide, SO₃


• 
  Higher sulfur oxides, SO_x where x>3

Selenium chalcogenides

Molecular structure of selenium trioxide.

• 
  Selenium dioxide, SeO₂


• 
  Selenium trioxide, SeO₃


• Many "alloys" of selenium and sulfur in different concentrations with semimetallic bonding, Se_xS_y
  • "Selenium monosulfide", SeS
  
  
  • "Selenium disulfide", SeS₂, actually a 2:1 mixture of cyclo-Se₃S₅ and cyclo-Se₂S₆
  
  
  • "Selenium trisulfide", SeS₃, actually occurring as the cyclic dimer Se₂S₆
  
  

Tellurium chalcogenides

Crystal structure of tellurium dioxide.

• 
  Tellurium monoxide, TeO (unstable transient species)


• 
  Tellurium dioxide, TeO₂


• 
  Tellurium trioxide, TeO₃


• 
  Ditellurium pentoxide, Te₂O₅^[2]


• Many "alloys" of tellurium and sulfur in different concentrations with semimetallic bonding, Te_xS_y


• Many "alloys" of tellurium and selenium in different concentrations with semimetallic bonding, Te_xSe_y

Polonium chalcogenides

Unit cell of polonium dioxide (cubic modification). Po: white; O: yellow.

• 
  Polonium monoxide, PoO


• 
  Polonium dioxide, PoO₂


• 
  Polonium trioxide, PoO₃


• 
  Polonium monosulfide, PoS


• Many "alloys" of polonium and selenium in different concentrations with semimetallic bonding, Po_xSe_y


• Many "alloys" of polonium and tellurium in different concentrations with semimetallic bonding, Po_xTe_y

See also

• Interhalogen


• Hydrogen chalcogenide

Notes

References