Editing Metalloid (section)

===Tellurium===
{{Main|Tellurium}}
[[File:Tellurium2.jpg|thumb|left|[[Tellurium]], described by [[Dmitri Mendeleev]] as forming a transition between [[metals]] and [[nonmetals]]<ref>[[#Mendeléeff1897a|Mendeléeff 1897, p.&nbsp;274]]</ref>|alt=A shiny silver-white medallion with a striated surface, irregular around the outside, with a square spiral-like pattern in the middle.]]
Tellurium is a silvery-white shiny solid.<ref>[[#Emsley2001|Emsley 2001, p.&nbsp;428]]</ref> It has a density of 6.24 g/cm<sup>3</sup>, is brittle, and is the softest of the commonly recognised metalloids, being marginally harder than sulfur.<ref name="GWM2011"/> Large pieces of tellurium are stable in air. The finely powdered form is oxidized by air in the presence of moisture. Tellurium reacts with boiling water, or when freshly precipitated even at 50&nbsp;°C, to give the dioxide and hydrogen: Te + 2 H<sub>2</sub>O → TeO<sub>2</sub> + 2 H<sub>2</sub>.<ref name=Kudryavtsev78>[[#Kudryavtsev1974|Kudryavtsev 1974, p.&nbsp;78]]</ref> It reacts (to varying degrees) with nitric, sulfuric, and hydrochloric acids to give compounds such as the [[sulfoxide]] TeSO<sub>3</sub> or [[tellurous acid]] H<sub>2</sub>TeO<sub>3</sub>,<ref>[[#Bagnall1966|Bagnall 1966, pp.&nbsp;32–33, 59, 137]]</ref> the basic nitrate (Te<sub>2</sub>O<sub>4</sub>H)<sup>+</sup>(NO<sub>3</sub>)<sup>−</sup>,<ref>[[#Swink1966|Swink et al. 1966]]; [[#Anderson1980|Anderson et al. 1980]]</ref> or the oxide sulfate Te<sub>2</sub>O<sub>3</sub>(SO<sub>4</sub>).<ref>[[#Ahmed2000|Ahmed, Fjellvåg & Kjekshus 2000]]</ref> It dissolves in boiling alkalis, to give the [[tellurite]] and [[telluride (chemistry)|telluride]]: 3 Te + 6 KOH = K<sub>2</sub>TeO<sub>3</sub> + 2 K<sub>2</sub>Te + 3 H<sub>2</sub>O, a reaction that proceeds or is reversible with increasing or decreasing temperature.<ref>[[#Chizhikov1970|Chizhikov & Shchastlivyi 1970, p.&nbsp;28]]</ref>

At higher temperatures tellurium is sufficiently plastic to extrude.<ref>[[#Kudryavtsev1974|Kudryavtsev 1974, p.&nbsp;77]]</ref> It melts at 449.51&nbsp;°C. Crystalline tellurium has a structure consisting of parallel infinite spiral chains. The bonding between adjacent atoms in a chain is covalent, but there is evidence of a weak metallic interaction between the neighbouring atoms of different chains.<ref name="Stuke1074p178">[[#Stuke1974|Stuke 1974, p.&nbsp;178]]; [[#Donohue1982|Donohue 1982, pp.&nbsp;386–87]]; [[#Cotton1999|Cotton et al. 1999, p.&nbsp;501]]</ref> Tellurium is a semiconductor with an electrical conductivity of around 1.0&nbsp;S•cm<sup>−1</sup><ref>[[#Becker1971|Becker, Johnson & Nussbaum 1971, p.&nbsp;56]]</ref> and a band gap of 0.32 to 0.38&nbsp;eV.<ref name=Berger90>[[#Berger1997|Berger 1997, p.&nbsp;90]]</ref> Liquid tellurium is a semiconductor, with an electrical conductivity, on melting, of around 1.9 × 10<sup>3</sup>&nbsp;S•cm<sup>−1</sup>.<ref name=Berger90/> [[Superheated]] liquid tellurium is a metallic conductor.<ref>[[#Chizhikov1970|Chizhikov & Shchastlivyi 1970, p.&nbsp;16]]</ref>

Most of the chemistry of tellurium is characteristic of a nonmetal.<ref>[[#Jolly1966|Jolly 1966, pp.&nbsp;66–67]]</ref>
It shows some cationic behaviour. The dioxide dissolves in acid to yield the trihydroxotellurium(IV) Te(OH)<sub>3</sub><sup>+</sup> ion;<ref>[[#Schwietzer2010|Schwietzer & Pesterfield 2010, p.&nbsp;239]]</ref>{{refn|1=Cotton et al.<ref>[[#Cotton1999|Cotton et al. 1999, p.&nbsp;498]]</ref> note that TeO<sub>2</sub> appears to have an ionic lattice; Wells<ref>[[#Wells1984|Wells 1984, p.&nbsp;715]]</ref> suggests that the Te–O bonds have "considerable covalent character".|group=n}} the red Te<sub>4</sub><sup>2+</sup> and yellow-orange Te<sub>6</sub><sup>2+</sup> ions form when tellurium is oxidized in [[fluorosulfuric acid]] (HSO<sub>3</sub>F), or liquid [[sulfur dioxide]] (SO<sub>2</sub>), respectively.<ref>[[#Wiberg2001|Wiberg 2001, p.&nbsp;588]]</ref> It can form alloys with aluminium, [[silver]], and tin.<ref>[[#Mellor1964a|Mellor 1964a, p.&nbsp; 30]]; [[#Wiberg2001|Wiberg 2001, p.&nbsp;589]]</ref> Tellurium shows fewer tendencies to anionic behaviour than ordinary nonmetals.<ref name=Cox/> Its solution chemistry is characterised by the formation of oxyanions.<ref name=Hiller225/> Tellurium generally forms compounds in which it has an oxidation state of −2, +4 or +6. The +4 state is the most stable.<ref name=Kudryavtsev78/> Tellurides of composition X<sub>''x''</sub>Te<sub>''y''</sub> are easily formed with most other elements and represent the most common tellurium minerals. [[Non-stoichiometric compound|Nonstoichiometry]] is pervasive, especially with transition metals. Many tellurides can be regarded as metallic alloys.<ref>[[#Greenwood2002|Greenwood & Earnshaw 2002, pp.&nbsp;765–66]]</ref> The increase in metallic character evident in tellurium, as compared to the lighter [[chalcogen]]s, is further reflected in the reported formation of various other oxyacid salts, such as a [[basic salt|basic]] selenate 2TeO<sub>2</sub>·SeO<sub>3</sub>  and an analogous perchlorate and [[periodate]] 2TeO<sub>2</sub>·HXO<sub>4</sub>.<ref>[[#Bagnall1966|Bagnall 1966, pp.&nbsp;134–51]]; [[#Greenwood2002|Greenwood & Earnshaw 2002, p.&nbsp;786]]</ref> Tellurium forms a polymeric,<ref name=Pudd59/> amphoteric,<ref name="Wiberg2001p764"/> glass-forming oxide<ref name=Rao22/> TeO<sub>2</sub>. It is a "conditional" glass-forming oxide – it forms a glass with a very small amount of additive.<ref name=Rao22/> Tellurium has an extensive organometallic chemistry (see [[Organotellurium chemistry]]).<ref>[[#Detty1994|Detty & O'Regan 1994, pp.&nbsp;1–2]]</ref>