Editing Chalcogen (section)

===With pnictogens===

[[File:Sulfid bismutitý.PNG|thumb|Bismuth sulfide, a pnictogen chalcogenide]]
Compounds with chalcogen-[[phosphorus]] bonds have been explored for more than 200 years. These compounds include unsophisticated phosphorus chalcogenides as well as large molecules with biological roles and phosphorus-chalcogen compounds with metal clusters. These compounds have numerous applications, including organo-phosphate insecticides, [[Match#The strike-anywhere match|strike-anywhere matches]] and [[quantum dot]]s. A total of 130,000 compounds with at least one phosphorus-sulfur bond, 6000 compounds with at least one phosphorus-selenium bond, and 350 compounds with at least one phosphorus-tellurium bond have been discovered.{{citation needed|date=September 2014}} The decrease in the number of chalcogen-phosphorus compounds further down the periodic table is due to diminishing bond strength. Such compounds tend to have at least one phosphorus atom in the center, surrounded by four chalcogens and [[side chain]]s. However, some phosphorus-chalcogen compounds also contain hydrogen (such as secondary [[phosphine]] chalcogenides) or nitrogen (such as dichalcogenoimidodiphosphates). [[Phosphorus selenide]]s are typically harder to handle that phosphorus sulfides, and compounds in the form P<sub>x</sub>Te<sub>y</sub> have not been discovered. Chalcogens also bond with other [[pnictogens]], such as [[arsenic]], [[antimony]], and [[bismuth]]. Heavier chalcogen pnictides tend to form [[ribbon]]-like polymers instead of individual molecules. Chemical formulas of these compounds include Bi<sub>2</sub>S<sub>3</sub> and Sb<sub>2</sub>Se<sub>3</sub>. Ternary chalcogen pnictides are also known. Examples of these include P<sub>4</sub>O<sub>6</sub>Se and P<sub>3</sub>SbS<sub>3</sub>. [[Salt (chemistry)|salts]] containing chalcogens and pnictogens also exist. Almost all chalcogen pnictide salts are typically in the form of [Pn<sub>x</sub>E<sub>4x</sub>]<sup>3−</sup>, where Pn is a pnictogen and E is a chalcogen.{{dubious|date=September 2014}} Tertiary phosphines can react with chalcogens to form compounds in the form of R<sub>3</sub>PE, where E is a chalcogen. When E is sulfur, these compounds are relatively stable, but they are less so when E is selenium or tellurium. Similarly, secondary phosphines can react with chalcogens to form secondary phosphine chalcogenides. However, these compounds are in a state of [[Chemical equilibrium|equilibrium]] with chalcogenophosphinous acid. Secondary phosphine chalcogenides are [[weak acids]].<ref name="handbook"/> Binary compounds consisting of antimony or arsenic and a chalcogen. These compounds tend to be colorful and can be created by a reaction of the constituent elements at temperatures of {{convert|500|to|900|C|F}}.<ref>{{Citation|author1=A. Earnshaw |author2=Norman Greenwood |url = https://books.google.com/books?id=EvTI-ouH3SsC&q=chalcogen|title = Chemistry of the Elements|date = November 11, 1997|publisher=Elsevier |access-date = February 12, 2014|isbn = 9780080501093}}</ref>