Editing Metalloid (section)

===Carbon===
{{Main|Carbon}}
[[File:Graphite2.jpg|thumb|right|[[Carbon]] (as [[graphite]]). [[Delocalized electron|Delocalized valence electrons]] within the layers of graphite give it a metallic appearance.<ref>[[#Hill2000|Hill & Holman 2000, p.&nbsp;124]]</ref>|alt=A shiny grey-black cuboid nugget with a rough surface.]]
Carbon is ordinarily classified as a nonmetal<ref>[[#Chang2002|Chang 2002, p.&nbsp;314]]</ref> but has some metallic properties and is occasionally classified as a metalloid.<ref>[[#Kent1950|Kent 1950, pp.&nbsp;1–2]]; [[#Clark1960|Clark 1960, p.&nbsp;588]]; [[#Warren1981|Warren & Geballe 1981]]</ref> [[Graphite|Hexagonal graphitic carbon]] (graphite) is the most thermodynamically stable [[allotrope]] of carbon under ambient conditions.<ref>[[#Housecroft2008|Housecroft & Sharpe 2008, p.&nbsp;384]]; [[#IUPAC2006|IUPAC 2006–, rhombohedral graphite entry]]</ref> It has a lustrous appearance<ref>[[#Mingos1998|Mingos 1998, p.&nbsp;171]]</ref> and is a fairly good electrical conductor.<ref>[[#Wiberg2001|Wiberg 2001, p.&nbsp;781]]</ref> Graphite has a layered structure. Each layer consists of carbon atoms bonded to three other carbon atoms in a [[hexagonal lattice]] arrangement. The layers are stacked together and held loosely by [[van der Waals force]]s and [[delocalized electron|delocalized valence electrons]].<ref>[[#Charlier|Charlier, Gonze & Michenaud 1994]]</ref>

The electrical conductivity of graphite is high parallel to its planes (30 kS/cm at 25°C), and decreases with increasing temperature, indicating [[Semimetal|semimetallic]] behaviour along that direction. Perpendicular to the planes, graphite behaves as a [[semiconductor]]: the conductivity is low (5 S/cm) but increases as the temperature rises.<ref name="Atkins320">[[Metalloid#Atkins2006|Atkins et al. 2006, pp.&nbsp;320–21]]</ref>{{refn|1=Liquid carbon may<ref>[[#Savvatimskiy2005|Savvatimskiy 2005, p.&nbsp;1138]]</ref> or may not<ref>[[#Togaya2000|Togaya 2000]]</ref> be a metallic conductor, depending on pressure and temperature; see also.<ref>[[#Savvatimskiy2009|Savvatimskiy 2009]]</ref>|group=n}} The allotropes of carbon, including graphite, can accept foreign atoms or compounds into their structures via substitution, [[intercalation (chemistry)|intercalation]], or [[dopant|doping]]. The resulting materials are sometimes referred to as "carbon alloys".<ref>[[#Inagaki2000|Inagaki 2000, p.&nbsp;216]]; [[#Yasuda2003|Yasuda et al. 2003, pp.&nbsp;3–11]]</ref> Carbon can form ionic salts, including a hydrogen sulfate, perchlorate, and nitrate (C{{su|b=24|p=+}}X<sup>−</sup>.2HX, where X = HSO<sub>4</sub>, ClO<sub>4</sub>; and C{{su|b=24|p=+}}NO{{su|b=3|p=–}}.3HNO<sub>3</sub>).<ref>[[#O'Hare|O'Hare 1997, p.&nbsp;230]]</ref>{{refn|1=For the sulfate, the method of preparation is (careful) direct oxidation of graphite in concentrated sulfuric acid by an [[oxidising agent]], such as [[nitric acid]], [[chromium trioxide]] or [[ammonium persulfate]]; in this instance the concentrated sulfuric acid is acting as an [[inorganic nonaqueous solvent]].|group=n}} In [[organic chemistry]], carbon can form complex cations{{snd}}termed [[carbocation|''carbocations'']]{{snd}}in which the positive charge is on the carbon atom; examples are [[carbenium ion|{{chem|CH|3|+}}]] and [[carbonium ion|{{chem|CH|5|+}}]], and their derivatives.<ref>[[#Traynham1989|Traynham 1989, pp.&nbsp;930–31]]; [[#Prakash1997|Prakash & Schleyer 1997]]</ref>

Graphite is an established solid lubricant and behaves as a semiconductor in a direction perpendicular to its planes.<ref name=Atkins320/> Most of its chemistry is nonmetallic;<ref>[[#Bailar1989|Bailar et al. 1989, p.&nbsp;743]]</ref> it has a relatively high ionization energy<ref>[[#Moore1985|Moore et al. 1985]]</ref> and, compared to most metals, a relatively high electronegativity.<ref>[[#House2010|House & House 2010, p.&nbsp;526]]</ref> Carbon can form anions such as C<sup>4−</sup> ([[methanide]]), C{{su|b=2|p=2–}} ([[acetylide]]), and C{{su|b=4|p=3–}} ([[Sesquicarbide|sesquicarbide or allylenide]]), in compounds with metals of main groups 1–3, and with the [[lanthanide]]s and [[actinide]]s.<ref>[[#Wiberg2001|Wiberg 2001, p.&nbsp;798]]</ref> Its oxide [[carbon dioxide|CO<sub>2</sub>]] forms [[carbonic acid]] H<sub>2</sub>CO<sub>3</sub>.<ref>[[#Eagleson1994|Eagleson 1994, p.&nbsp;175]]</ref>{{refn|1=Only a small fraction of dissolved CO<sub>2</sub> is present in water as carbonic acid so, even though H<sub>2</sub>CO<sub>3</sub> is a medium-strong acid, solutions of carbonic acid are only weakly acidic.<ref>[[#Atkins2006|Atkins et al. 2006, p.&nbsp;121]]</ref>|group=n}}