Editing Tellurium (section)

===Oxocompounds===
[[File:TeO2powder.jpg|thumb|alt=A sample of pale yellow powder|A sample of tellurium dioxide powder]]
Tellurium monoxide was first reported in 1883 as a black amorphous solid formed by the heat decomposition of {{chem|TeSO|3}} in vacuum, disproportionating into [[tellurium dioxide]], {{chem|TeO|2}} and elemental tellurium upon heating.<ref>{{cite encyclopedia|encyclopedia = Encyclopedia of materials, parts, and finishes|title = Tellurium|first = Mel M.|last = Schwartz|edition = 2nd|publisher = CRC Press|date = 2002|isbn = 1-56676-661-3}}</ref><ref name="divers">{{Cite journal|journal = Journal of the Chemical Society|title = On a new oxide of tellurium|first1 = Edward|last1 = Divers|first2 = M.|last2 = Shimosé|volume = 43|doi = 10.1039/CT8834300319|date = 1883|pages = 319–323|url = https://zenodo.org/record/2170636}}</ref> Since then, however, existence in the solid phase is doubted and in dispute, although it is known as a vapor fragment; the black solid may be merely an equimolar mixture of elemental tellurium and tellurium dioxide.<ref name="dutton">{{cite journal |last1 = Dutton |first1 = W. A. |last2 = Cooper |first2 = W. Charles |title = The Oxides and Oxyacids of Tellurium |journal = Chemical Reviews |volume = 66 |pages = 657–675 |date = 1966 |doi = 10.1021/cr60244a003 |issue = 6}}</ref>

Tellurium dioxide is formed by heating tellurium in air, where it burns with a blue flame.<ref name="roscoe">{{Cite book|title = A treatise on chemistry|volume = 1|first1 = Henry Enfield|last1 = Roscoe|author-link1 = Henry Enfield Roscoe|first2 = Carl|author-link2 = Carl Schorlemmer|publisher = Appleton|date = 1878|pages = 367–368|last2 = Schorlemmer}}</ref> Tellurium trioxide, β-{{chem|TeO|3}}, is obtained by thermal decomposition of {{chem|Te(OH)|6}}. The other two forms of trioxide reported in the literature, the α- and γ- forms, were found not to be true oxides of tellurium in the +6 oxidation state, but a mixture of {{chem|Te|4+}}, {{chem|OH|-}} and {{chem|O|2|-}}.<ref name="wickleder">{{Cite book|title = Handbook of chalcogen chemistry: new perspectives in sulfur, selenium and tellurium|url = https://archive.org/details/handbookchalcoge00devi_741|url-access = limited|chapter = Chalcogen-Oxygen Chemistry|first1 = Mathias S.|last1 = Wickleder|editor = Francesco A. Devillanova|publisher = Royal Society of Chemistry|date = 2007|isbn = 978-0-85404-366-8|pages = [https://archive.org/details/handbookchalcoge00devi_741/page/n366 348]–350}}</ref> Tellurium also exhibits mixed-valence oxides, {{chem|Te|2|O|5}} and {{chem|Te|4|O|9}}.<ref name="wickleder" />

The tellurium oxides and hydrated oxides form a series of acids, including [[tellurous acid]] ({{chem|H|2|TeO|3}}), [[telluric acid|orthotelluric acid]] ({{chem|Te(OH)|6}}) and metatelluric acid ({{chem|(H|2|TeO|4|)|''n''}}).<ref name="dutton" /> The two forms of telluric acid form ''[[tellurate]]'' salts containing the TeO{{su|b=4|p=2–}} and TeO{{su|b=6|p=6−}} anions, respectively. Tellurous acid forms ''[[tellurite]]'' salts containing the anion TeO{{su|b=3|p=2−}}.<ref>[[#Greenwood|Greenwood]], p. 748</ref>