Editing Metalloid (section)

===Silicon===
{{Main|Silicon}}
[[File:SiliconCroda.jpg|thumb|left|[[Silicon]] has a blue-grey metallic [[lustre (mineralogy)|lustre]].|alt=A lustrous blue grey potato-shaped lump with an irregular corrugated surface.]]
Silicon is a crystalline solid with a blue-grey metallic lustre.<ref name=Greenwood331>[[#Greenwood2002|Greenwood & Earnshaw 2002, p.&nbsp;331]]</ref> Like boron, it is less dense (at 2.33 g/cm<sup>3</sup>) than aluminium, and is hard and brittle.<ref>[[#Wiberg2001|Wiberg 2001, p.&nbsp;824]]</ref> It is a relatively unreactive element.<ref name=Greenwood331/> According to Rochow,<ref>[[#Rochow1973|Rochow 1973, pp.&nbsp;1337‒38]]</ref> the massive crystalline form (especially if pure) is "remarkably inert to all acids, including [[hydrofluoric acid|hydrofluoric]]".{{refn|1=In air, silicon forms a thin coating of amorphous silicon dioxide, 2 to 3 nm thick.<ref name=R393/> This coating is dissolved by [[hydrogen fluoride]] at a very low pace – on the order of two to three hours per nanometre.<ref>[[#Zhang|Zhang 2002, p.&nbsp;70]]</ref> Silicon dioxide, and silicate glasses (of which silicon dioxide is a major component), are otherwise readily attacked by hydrofluoric acid.<ref>[[#Sacks|Sacks 1998, p.&nbsp;287]]</ref>|group=n}} Less pure silicon, and the powdered form, are variously susceptible to attack by strong or heated acids, as well as by steam and fluorine.<ref>[[#Rochow1973|Rochow 1973, pp.&nbsp;1337, 1340]]</ref> Silicon dissolves in hot aqueous [[alkali]]s with the evolution of [[hydrogen]], as do metals<ref>[[#Allen1968|Allen & Ordway 1968, p.&nbsp;152]]</ref> such as beryllium, aluminium, zinc, gallium or indium.<ref>[[#Eagleson1994|Eagleson 1994, pp.&nbsp;48, 127, 438, 1194]]; [[#Massey2000|Massey 2000, p.&nbsp;191]]</ref> It melts at 1414&nbsp;°C. Silicon is a semiconductor with an electrical conductivity of 10<sup>−4</sup>&nbsp;S•cm<sup>−1</sup><ref>[[#Orton2004|Orton 2004, p.&nbsp;7]]. This is a typical value for high-purity silicon.</ref> and a band gap of about 1.11&nbsp;eV.<ref name=R393>[[#Russell2005|Russell & Lee 2005, p.&nbsp;393]]</ref> When it melts, silicon becomes a reasonable metal<ref>[[#Coles1976|Coles & Caplin 1976, p.&nbsp;106]]</ref> with an electrical conductivity of 1.0–1.3 × 10<sup>4</sup>&nbsp;S•cm<sup>−1</sup>, similar to that of liquid mercury.<ref>[[#Glazov1969|Glazov, Chizhevskaya & Glagoleva 1969, pp.&nbsp;59–63]]; [[#Allen1987|Allen & Broughton 1987, p.&nbsp;4967]]</ref>

The chemistry of silicon is generally nonmetallic (covalent) in nature.<ref>[[#Cotton1995|Cotton, Wilkinson & Gaus 1995, p.&nbsp;393]]</ref> It is not known to form a cation.<ref>[[#Wiberg2001|Wiberg 2001, p.&nbsp;834]]</ref>{{refn|1=The bonding in [[silicon tetrafluoride]], a gas, has been referred to as predominately ionic<ref name=Gillespie1998/> a description which was subsequently described as misleading.<ref name=Haaland/>|group=n}} Silicon can form alloys with metals such as iron and copper.<ref>[[#Partington1944|Partington 1944, p.&nbsp;723]]</ref> It shows fewer tendencies to anionic behaviour than ordinary nonmetals.<ref name=Cox>[[#Cox2004|Cox 2004, p.&nbsp;27]]</ref> Its solution chemistry is characterised by the formation of oxyanions.<ref name=Hiller225>[[#Hiller1960|Hiller & Herber 1960, inside front cover; p.&nbsp;225]]</ref> The high strength of the [[silicon–oxygen bond]] dominates the chemical behaviour of silicon.<ref>[[#Kneen1972|Kneen, Rogers and Simpson 1972, p.&nbsp;384]]</ref> Polymeric silicates, built up by tetrahedral SiO<sub>4</sub> units sharing their oxygen atoms, are the most abundant and important compounds of silicon.<ref name="Bailar513"/> The polymeric borates, comprising linked trigonal and tetrahedral BO<sub>3</sub> or BO<sub>4</sub> units, are built on similar structural principles.<ref>[[#Cotton1995|Cotton, Wilkinson & Gaus 1995, pp.&nbsp;319, 321]]</ref> The oxide SiO<sub>2</sub> is polymeric in structure,<ref name=Pudd59/> weakly acidic,<ref>[[#Smith1990|Smith 1990, p.&nbsp;175]]</ref>{{refn|1=Although SiO<sub>2</sub> is classified as an acidic oxide, and hence reacts with alkalis to give silicates, it reacts with phosphoric acid to yield a silicon oxide orthophosphate Si<sub>5</sub>O(PO<sub>4</sub>)<sub>6</sub>,<ref>[[#Poojary1993|Poojary, Borade & Clearfield 1993]]</ref> and with hydrofluoric acid to give [[hexafluorosilicic acid]] H<sub>2</sub>SiF<sub>6</sub>.<ref>[[#Wiberg2001|Wiberg 2001, pp.&nbsp;851, 858]]</ref> The latter reaction "is sometimes quoted as evidence of basic [that is, metallic] properties".<ref>[[#Barnett|Barmett & Wilson 1959, p.&nbsp;332]]</ref>|group=n}} and a glass former.<ref name=Rao22/> Traditional organometallic chemistry includes the carbon compounds of silicon (see [[organosilicon]]).<ref>[[#Powell1988|Powell 1988, p.&nbsp;1]]</ref>