The chalcogens react with each other to form '''interchalcogen''' compounds.<ref name="Holleman&Wiberg"/>
Although no chalcogen is extremely electropositive,<ref group="note">This article uses Pauling electronegativity throughout.</ref> 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<ref group="note" name="Po">The classification of polonium as a post-transition metal or a metalloid is disputed.</ref>), this causes the interchalcogens to display many different kinds of bonding: covalent, ionic, metallic, and semimetallic.<ref group="note">The heavier halogens are sufficiently electronegative to prevent ionic or metallic bonding in the interhalogens, and the lighter pnictogens are not sufficiently electronegative to allow ionic or metallic bonding in the interpnictogens.</ref><ref name="Holleman&Wiberg">{{Holleman&Wiberg|pages=585–586}}</ref>
==Known binary interchalcogens== {| class="wikitable" style="margin: 1em auto 1em auto" ! || O |- | '''O''' || <div class="center">{{chem2|O2, O3, O4, O8}}</div> || bgcolor="#eeeeee" | {{center|'''S'''}} |- | '''S''' || <div class="center">{{chem2|S2O, SO, S2O2, SO2, SO3}}</div> || <div class="center">{{chem2|S2, S3, S6, S7, S8, S_{∞}}}</div> || bgcolor="#eeeeee" | {{center|'''Se'''}} |- | '''Se''' || <div class="center">{{chem2|SeO2, SeO3}}</div> || <div class="center">{{chem2|Se_{''x''}S_{''y''}|}}</div> || <div class="center">{{chem2|Se6, Se7, Se8, Se_{∞}}}</div> || bgcolor="#eeeeee | {{center|'''Te'''}} |- | '''Te''' || <div class="center">{{chem2|TeO, TeO2, TeO3, Te2O5}}</div> || <div class="center">{{chem2|Te_{''x''}S_{''y''}|}} (many unknown)</div> || <div class="center">{{chem2|Te_{''x''}Se_{''y''}|}} (many unknown)</div>|| <div class="center">{{chem2|Te_{∞}}}</div> || bgcolor="#eeeeee" |{{center|'''Po'''}} |- | '''Po''' || <div class="center">{{chem2|PoO, PoO2, PoO3}}</div> || {{center|PoS}} (many unknown) || <div class="center">{{chem2|Po_{''x''}Se_{''y''}|}}</div> (many unknown) || <div class="center">{{chem2|Po_{''x''}Te_{''y''}|}}</div> (unknown) || <div class="center">{{chem2|Po_{∞}}}</div> |}
==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), {{chem2|O2}} and {{chem2|O3}} are purely covalent, {{chem2|SO2}} and {{chem2|SO3}} are polar molecules, {{chem2|SeO2}} forms chained polymers (stretching in one dimension), {{chem2|TeO2}} forms layered polymers (stretching in two dimensions), and {{chem2|PoO2}} is ionic with the fluorite structure (spatial polymers, stretching in three dimensions); in the bottom row of the table (with bonds to polonium), {{chem2|PoO2}} and PoS are ionic, {{chem2|Po_{''x''}Se_{''y''}|}} and {{chem2|Po_{''x''}Te_{''y''}|}} are semimetallic, and {{chem2|Po_{∞}|}} is metallic.<ref name="Holleman&Wiberg"/>
==Summary of known binary interchalcogens==
===Sulfur chalcogenides=== [[File:Sulfur-monoxide-3D-vdW.png|thumb|150px|right|Molecular structure of sulfur monoxide.]] *Lower sulfur oxides, {{chem2|S_{''x''}O_{''y''}|}} where the ratio ''x'':''y'' is greater than 1:2 **Disulfur monoxide, {{chem2|S2O}} **Disulfur dioxide, {{chem2|S2O2}} **Sulfur monoxide, SO *Sulfur dioxide, {{chem2|SO2}} *Sulfur trioxide, {{chem2|SO3}} *Higher sulfur oxides, {{chem2|SO_{''x''}|}} where ''x'' > 3
===Selenium chalcogenides=== [[File:Selenium-trioxide-3D-spacefill.png|thumb|150px|right|Molecular structure of selenium trioxide.]] *Selenium dioxide, {{chem2|SeO2}} *Selenium trioxide, {{chem2|SeO3}} *Many "alloys" of selenium and sulfur in different concentrations with semimetallic bonding, {{chem2|Se_{''x''}S_{''y''}|}} **"Selenium monosulfide", SeS **"Selenium disulfide", {{chem2|SeS2}}, actually a 2:1 mixture of ''cyclo''-{{chem2|Se3S5}} and ''cyclo''-{{chem2|Se2S6}} **"Selenium trisulfide", {{chem2|SeS3}}, actually occurring as an 8-membered cyclic compound {{chem2|Se2S6}} (diselenacyclooctasulfane), where two sulfur atoms in the molecule of cyclooctasulfur are replaced by selenium atoms
===Tellurium chalcogenides=== [[File:Cryst struct teo2.png|thumb|150px|right|Crystal structure of tellurium dioxide.]] *Tellurium monoxide, TeO (unstable transient species) *Tellurium dioxide, {{chem2|TeO2}} *Tellurium trioxide, {{chem2|TeO3}} *Ditellurium pentoxide, {{chem2|Te2O5}}<ref>{{Cite journal|url=http://scripts.iucr.org/cgi-bin/paper?S0567740873003092|doi = 10.1107/S0567740873003092|title = The crystal structure of ditellurium pentoxide, Te2O5|year = 1973|last1 = Lindqvist|first1 = O.|last2 = Moret|first2 = J.|journal = Acta Crystallographica Section B: Structural Crystallography and Crystal Chemistry|volume = 29|issue = 4|pages = 643–650|url-access = subscription}}</ref> *Many "alloys" of tellurium and sulfur in different concentrations with semimetallic bonding, {{chem2|Te_{''x''}S_{''y''}|}} *Many "alloys" of tellurium and selenium in different concentrations with semimetallic bonding, {{chem2|Te_{''x''}Se_{''y''}|}}
===Polonium chalcogenides=== [[File:Fluorite-unit-cell-3D-balls.png|thumb|150px|right|Unit cell of polonium dioxide (cubic modification). Po: white; O: yellow.]] *Polonium monoxide, PoO *Polonium dioxide, {{chem2|PoO2}} *Polonium trioxide, {{chem2|PoO3}} *Polonium monosulfide, PoS *Many "alloys" of polonium and selenium in different concentrations with semimetallic bonding, {{chem2|Po_{''x''}Se_{''y''}|}} *Many "alloys" of polonium and tellurium in different concentrations with semimetallic bonding, {{chem2|Po_{''x''}Te_{''y''}|}}
==See also== *Interhalogen *Hydrogen chalcogenide
==Notes== {{reflist|group=note}}
==References== {{reflist}}
* Category:Chalcogens