Editing Carbon (section)

===Allotropes===
{{Main|Allotropes of carbon}}
[[Atomic carbon]] is a very short-lived species and, therefore, carbon is stabilized in various multi-atomic structures with diverse molecular configurations called [[allotrope]]s. The three relatively well-known allotropes of carbon are [[amorphous carbon]], [[graphite]], and diamond. Once considered exotic, [[fullerene]]s are nowadays commonly synthesized and used in research; they include [[buckyball]]s,<ref name="Unwin-2007"/><ref name="Ebbesen-1997">{{cite book |editor=Ebbesen, T. W. |editor-link=Thomas Ebbesen |date=1997 |title=Carbon nanotubes—preparation and properties |publisher=CRC Press |location=Boca Raton, Florida |isbn=978-0-8493-9602-1}}</ref> [[carbon nanotube]]s,<ref name="Springer-2001">{{cite book |editor=Dresselhaus, M. S. |editor-link1=Mildred Dresselhaus |editor2=Dresselhaus, G. |editor3=Avouris, Ph. |editor-link3=Phaedon Avouris |date=2001 |title=Carbon nanotubes: synthesis, structures, properties and applications |series=Topics in Applied Physics |volume=80 |isbn=978-3-540-41086-7 |location=Berlin |publisher=Springer}}</ref> [[carbon nanobud]]s<ref name="Nasibulin-2007">{{cite journal |date=2007 |title=A novel hybrid carbon material |journal=Nature Nanotechnology |volume=2 |issue=3 |pages=156–161 |doi=10.1038/nnano.2007.37 |pmid=18654245 |s2cid=6447122 |bibcode=2007NatNa...2..156N |doi-access=free |last1=Nasibulin |first1=Albert G. |author-link1=Albert Nasibulin |last2=Pikhitsa |first2=P. V. |last3=Jiang |first3=H. |last4=Brown |first4=D. P. |last5=Krasheninnikov |first5=A. V. |last6=Anisimov |first6=A. S. |last7=Queipo |first7=P. |last8=Moisala |first8=A. |last9=Gonzalez |first9=D. |display-authors=8}}</ref> and [[carbon nanofibers|nanofibers]].<ref>{{cite journal |date=2007 |title=Investigations of NanoBud formation |journal=Chemical Physics Letters |volume=446 |issue=1 |pages=109–114 |doi=10.1016/j.cplett.2007.08.050 |bibcode=2007CPL...446..109N |last1=Nasibulin |first1=A. |last2=Anisimov |first2=Anton S. |last3=Pikhitsa |first3=Peter V. |last4=Jiang |first4=Hua |last5=Brown |first5=David P. |last6=Choi |first6=Mansoo |last7=Kauppinen |first7=Esko I.}}</ref><ref>{{cite journal |date=2004 |title=Synthesis and characterisation of carbon nanofibers with macroscopic shaping formed by catalytic decomposition of C{{sub |2}}H{{sub|6}}/H{{sub|2}} over nickel catalyst |journal=Applied Catalysis A: General|volume=274|issue=1–2|pages=1–8|doi=10.1016/j.apcata.2004.04.008 |author=Vieira, R |last2=Ledoux|first2=Marc-Jacques |last3=Pham-Huu|first3=Cuong}}</ref> Several other exotic allotropes have also been discovered, such as [[lonsdaleite]],<ref name="Frondel-1967">{{cite journal |date=1967 |title=Lonsdaleite, a new hexagonal polymorph of diamond |journal=Nature |volume=214 |pages=587–589 |issue=5088 |bibcode=1967Natur.214..587F |s2cid=4184812 |doi=10.1038/214587a0 |first1=Clifford |last1=Frondel |last2=Marvin |first2=Ursula B. |author-link2=Ursula Marvin}}</ref> [[glassy carbon]],<ref name="Harris-2004"/> [[carbon nanofoam]]<ref>{{cite journal |date=1999 |title=Structural analysis of a carbon foam formed by high pulse-rate laser ablation |journal=Applied Physics A: Materials Science & Processing |volume=69 |pages=S755–S758 |doi=10.1007/s003390051522 |issue=7 |bibcode=1999ApPhA..69S.755R |s2cid=96050247 |author=Rode, A. V. |last2=Hyde |first2=S. T. |last3=Gamaly |first3=E. G. |last4=Elliman |first4=R. G. |last5=McKenzie |first5=D. R. |last6=Bulcock |first6=S.}}</ref> and [[linear acetylenic carbon]] (carbyne).<ref name="Heimann-1999">{{cite book |author=Heimann, Robert Bertram |author2=Evsyukov, Sergey E. |author3=Kavan, Ladislav |name-list-style=amp |title=Carbyne and carbynoid structures |url=https://books.google.com/books?id=swSQZcTmo_4C&pg=PA1 |access-date=2011-06-06 |date=28 February 1999 |publisher=Springer |isbn=978-0-7923-5323-2 |pages=1– |url-status=live |archive-url=https://web.archive.org/web/20121123153424/http://books.google.com/books?id=swSQZcTmo_4C&pg=PA1 |archive-date=23 November 2012}}</ref>

[[Graphene]] is a two-dimensional sheet of carbon with the atoms arranged in a hexagonal lattice. As of 2009, graphene appears to be the strongest material ever tested.<ref name="Lee-2008">{{cite journal |last1=Lee |first1=C. |last2=Wei |first2=X. |last3=Kysar |first3=J. W. |last4=Hone |first4=J. |date=2008 |title=Measurement of the Elastic Properties and Intrinsic Strength of Monolayer Graphene |journal=Science |volume=321 |issue=5887 |pages=385–8 |bibcode=2008Sci...321..385L |doi=10.1126/science.1157996 |pmid=18635798 |s2cid=206512830}}
* {{cite press release |author=Phil Schewe |date=July 28, 2008 |title=World's Strongest Material |website=Inside Science News Service |url=http://www.aip.org/isns/reports/2008/027.html |archive-url=https://web.archive.org/web/20090531134104/http://www.aip.org/isns/reports/2008/027.html |archive-date=2009-05-31}}</ref> The process of separating it from graphite will require some further technological development before it is economical for industrial processes.<ref name="Sanderson-2008">{{cite web |url=http://www.nypost.com/seven/08252008/news/regionalnews/toughest_stuff__known_to_man_125993.htm |title=Toughest Stuff Known to Man : Discovery Opens Door to Space Elevator |last=Sanderson |first=Bill |date=2008-08-25 |publisher=nypost.com |access-date=2008-10-09 |url-status=live |archive-url=https://web.archive.org/web/20080906171324/http://www.nypost.com/seven/08252008/news/regionalnews/toughest_stuff__known_to_man_125993.htm |archive-date=2008-09-06}}</ref> If successful, graphene could be used in the construction of a [[space elevator]]. It could also be used to safely store hydrogen for use in a hydrogen based engine in cars.<ref>{{cite journal |last1=Jin |first1=Zhong |last2=Lu |first2=Wei |last3=O'Neill |first3=Kevin J. |last4=Parilla |first4=Philip A. |last5=Simpson |first5=Lin J. |last6=Kittrell |first6=Carter |last7=Tour |first7=James M. |date=2011-02-22 |title=Nano-Engineered Spacing in Graphene Sheets for Hydrogen Storage |journal=Chemistry of Materials |volume=23 |issue=4 |pages=923–925 |doi=10.1021/cm1025188 |issn=0897-4756}}</ref>

[[File:Glassy carbon and a 1cm3 graphite cube HP68-79.jpg|thumb|left|A large sample of glassy carbon]] The [[amorphous]] form is an assortment of carbon atoms in a non-crystalline, irregular, glassy state, not held in a crystalline macrostructure. It is present as a powder, and is the main constituent of substances such as charcoal, [[lampblack]] (soot), and [[activated carbon]]. At normal pressures, carbon takes the form of graphite, in which each atom is bonded trigonally to three others in a plane composed of fused [[hexagon]]al rings, just like those in [[aromatic hydrocarbon]]s.<ref>{{cite book |title=The polymorphism of elements and compounds |last=Jenkins |first=Edgar |date=1973 |publisher=Taylor & Francis |isbn=978-0-423-87500-3 |page=30 |url=https://books.google.com/books?id=XNYOAAAAQAAJ&pg=PA30 |access-date=2011-05-01 |url-status=live |archive-url=https://web.archive.org/web/20121123204229/http://books.google.com/books?id=XNYOAAAAQAAJ&pg=PA30 |archive-date=2012-11-23}}</ref> The resulting network is 2-dimensional, and the resulting flat sheets are stacked and loosely bonded through weak [[van der Waals force]]s.<!-- no evidence for upper case van der Waals; see [[Talk:Van der Waals#Van should be capitalized unless preceded by first name]] rebuttal --> This gives graphite its softness and its [[cleavage (crystal)|cleaving]] properties (the sheets slip easily past one another). Because of the delocalization of one of the outer electrons of each atom to form a [[delocalized electron|π-cloud]], graphite conducts [[electricity]], but only in the plane of each [[covalently bonded]] sheet. This results in a lower bulk [[electrical conductivity]] for carbon than for most metals. The delocalization also accounts for the energetic stability of graphite over diamond at room temperature.{{sfn|Greenwood|Earnshaw|1997|pages=274-278}}

[[File:Eight Allotropes of Carbon.svg|thumb|upright=1.35|Some allotropes of carbon: a) [[diamond]]; b) [[graphite]]; c) [[lonsdaleite]]; d–f) [[fullerene]]s (C{{sub|60}}, C{{sub|540}}, C{{sub|70}}); g) [[amorphous carbon]]; h) [[carbon nanotube]]]]

At very high pressures, carbon forms the more compact allotrope, diamond, having nearly twice the density of graphite. Here, each atom is bonded [[tetrahedron|tetrahedrally]] to four others, forming a 3-dimensional network of puckered six-membered rings of atoms. Diamond has the same [[cubic structure]] as [[silicon]] and [[germanium]], and because of the strength of the carbon-carbon [[chemical bond|bonds]], it is the hardest naturally occurring substance measured by [[Mohs scale|resistance to scratching]]. Contrary to the popular belief that ''"diamonds are forever"'', they are thermodynamically unstable ([[Standard Gibbs free energy of formation|Δ<sub>f</sub>''G''°]](diamond, 298&nbsp;K) = 2.9&nbsp;kJ/mol<ref>{{cite journal |last1=Rossini |first1=F. D. |last2=Jessup |first2=R. S. |date=1938 |title=Heat and Free Energy of Formation of Carbon Dioxide and of the Transition Between Graphite and Diamond |journal=Journal of Research of the National Bureau of Standards |volume=21 |issue=4 |pages=491 |doi=10.6028/jres.021.028 |doi-access=free}}</ref>) under normal conditions (298&nbsp;K, 10<sup>5</sup>&nbsp;Pa) and should theoretically transform into graphite.<ref name="World of Carbon">{{cite web |url=http://invsee.asu.edu/nmodules/Carbonmod/point.html |archive-url=https://web.archive.org/web/20010531203728/http://invsee.asu.edu/nmodules/Carbonmod/point.html |url-status=dead |archive-date=2001-05-31 |title=World of Carbon&nbsp;– Interactive Nano-visulisation in Science & Engineering Education (IN-VSEE) |access-date=2008-10-09}}</ref> But due to a high [[activation energy]] barrier, the transition into graphite is so slow at normal temperature that it is unnoticeable. However, at very high temperatures diamond will turn into graphite, and diamonds can burn up in a house fire. The bottom left corner of the phase diagram for carbon has not been scrutinized experimentally. Although a computational study employing [[density functional theory]] methods reached the conclusion that as {{nowrap|''T'' → 0 K}} and {{nowrap|''p'' → 0 Pa}}, diamond becomes more stable than graphite by approximately 1.1&nbsp;kJ/mol,<ref>{{cite journal |last=Grochala |first=Wojciech |date=2014-04-01 |title=Diamond: Electronic Ground State of Carbon at Temperatures Approaching 0 K |journal=Angewandte Chemie International Edition |language=en |volume=53 |issue=14 |pages=3680–3683 |doi=10.1002/anie.201400131 |pmid=24615828 |issn=1521-3773 |s2cid=13359849}}</ref> more recent and definitive experimental and computational studies show that graphite is more stable than diamond for {{nowrap|''T'' < 400 K}}, without applied pressure, by 2.7&nbsp;kJ/mol at ''T''&nbsp;=&nbsp;0&nbsp;K and 3.2&nbsp;kJ/mol at ''T''&nbsp;=&nbsp;298.15&nbsp;K.<ref>{{cite journal |first1=Mary Anne |last1=White |author-link1=Mary Anne White |first2=Samer |last2=Kahwaji |first3=Vera L. S. |last3=Freitas |first4=Riko |last4=Siewert |first5=Joseph A. |last5=Weatherby |first6=Maria D. M. C. |last6=Ribeiro da Silva |first7=Sergey P. |last7=Verevkin |first8=Erin R. |last8=Johnson |first9=Josef W. |last9=Zwanziger |date=2021 |title=The Relative Thermal Stability of Diamond and Graphite |journal=Angewandte Chemie International Edition |language=en |volume=60 |issue=3 |pages=1546–1549 |doi=10.1002/anie.202009897 |issn=1433-7851 |pmid=32970365 |s2cid=221888151}}</ref> Under some conditions, carbon crystallizes as [[lonsdaleite]], a [[hexagonal crystal family|hexagonal crystal lattice]] with all atoms covalently bonded and properties similar to those of diamond.<ref name="Frondel-1967"/>

[[Fullerene]]s are a synthetic crystalline formation with a graphite-like structure, but in place of flat [[hexagonal crystal system|hexagonal cells]] only, some of the cells of which fullerenes are formed may be pentagons, nonplanar hexagons, or even heptagons of carbon atoms. The sheets are thus warped into spheres, ellipses, or cylinders. The properties of fullerenes (split into buckyballs, buckytubes, and nanobuds) have not yet been fully analyzed and represent an intense area of research in [[nanomaterial]]s. The names ''fullerene'' and ''buckyball'' are given after [[Richard Buckminster Fuller]], popularizer of [[geodesic dome]]s, which resemble the structure of fullerenes. The buckyballs are fairly large molecules formed completely of carbon bonded trigonally, forming [[spheroid]]s (the best-known and simplest is the soccerball-shaped C{{sub|60}} [[buckminsterfullerene]]).<ref name="Unwin-2007"/> Carbon nanotubes (buckytubes) are structurally similar to buckyballs, except that each atom is bonded trigonally in a curved sheet that forms a hollow [[cylinder]].<ref name="Ebbesen-1997"/><ref name="Springer-2001"/> Nanobuds were first reported in 2007 and are hybrid buckytube/buckyball materials (buckyballs are covalently bonded to the outer wall of a nanotube) that combine the properties of both in a single structure.<ref name="Nasibulin-2007"/>

[[File:C2014_Q2.jpg|thumb|Comet [[C/2014 Q2 (Lovejoy)]] surrounded by glowing carbon vapor]]
Of the other discovered allotropes, carbon nanofoam is a ferromagnetic allotrope discovered in 1997. It consists of a low-density cluster-assembly of carbon atoms strung together in a loose three-dimensional web, in which the atoms are bonded trigonally in six- and seven-membered rings. It is among the lightest known solids, with a density of about 2&nbsp;kg/m{{sup|3}}.<ref>{{cite journal |url=http://www.aip.org/pnu/2004/split/678-1.html |title=Carbon Nanofoam is the World's First Pure Carbon Magnet |journal=Physics News Update |url-status=live |volume=678 |issue=1 |date=March 26, 2004 |author=Schewe, Phil |author2=Stein, Ben |name-list-style=amp |archive-url=https://web.archive.org/web/20120307104655/http://www.aip.org/pnu/2004/split/678-1.html |archive-date=March 7, 2012}}</ref> Similarly, [[glassy carbon]] contains a high proportion of closed [[porosity]],<ref name="Harris-2004"/> but contrary to normal graphite, the graphitic layers are not stacked like pages in a book, but have a more random arrangement. [[Linear acetylenic carbon]]<ref name="Heimann-1999"/> has the chemical structure<ref name="Heimann-1999"/> −(C≡C){{sub|{{mvar|n}}}}−&nbsp;. Carbon in this modification is linear with ''sp'' [[orbital hybridization]], and is a [[polymer]] with alternating single and triple bonds. This carbyne is of considerable interest to [[nanotechnology]] as its [[Young's modulus]] is 40&nbsp;times that of the hardest known material&nbsp;– diamond.<ref>{{cite journal |last1=Itzhaki |first1=Lior |last2=Altus |first2=Eli |last3=Basch |first3=Harold |last4=Hoz |first4=Shmaryahu |year=2005 |title=Harder than diamond: Determining the cross-sectional area and Young's modulus of molecular rods |journal=Angew. Chem. Int. Ed. |volume=44 |issue=45 |pages=7432–7435 |pmid=16240306 |doi=10.1002/anie.200502448}}</ref>

In 2015, a team at the [[North Carolina State University]] announced the development of another allotrope they have dubbed [[Q-carbon]], created by a high-energy low-duration laser pulse on amorphous carbon dust. Q-carbon is reported to exhibit ferromagnetism, [[fluorescence]], and a hardness superior to diamonds.<ref>{{cite press release |title=Researchers find new phase of carbon, make diamond at room temperature |date=2015-11-30 |website=news.ncsu.edu |url=https://news.ncsu.edu/2015/11/narayan-q-carbon-2015/ |access-date=2016-04-06 |url-status=live |archive-url=https://web.archive.org/web/20160406002158/https://news.ncsu.edu/2015/11/narayan-q-carbon-2015/ |archive-date=2016-04-06}}</ref>

In the vapor phase, some of the carbon is in the form of highly reactive [[diatomic carbon]] dicarbon ({{chem2|C2}}). When excited, this gas glows green.<ref>{{cite journal | title = Chemistry of the singlet and triplet C<sub>2</sub> molecules. Mechanism of acetylene formation from reaction with acetone and acetaldehyde | first1 = Philip S. | last1 = Skell | author-link = Philip Skell | first2 = James H. | last2 = Plonka | journal = [[Journal of the American Chemical Society]] | year = 1970 | volume = 92 | issue = 19 | pages = 5620–5624| doi = 10.1021/ja00722a014| bibcode = 1970JAChS..92.5620S }}</ref><ref>{{cite journal |author1=J. Borsovszky |author2=K. Nauta |author3=J. Jiang |author4=C.S. Hansen |author5=L.K. McKemmish |author6=R.W. Field |author7=J.F. Stanton |author8=S.H. Kable |author9=T.W. Schmidt |title=Photodissociation of dicarbon: How nature breaks an unusual multiple bond |journal=Proceedings of the National Academy of Sciences of the United States of America |date=2021 |volume=118 |issue=52 |page=e2113315118 |doi=10.1073/pnas.2113315118 |doi-access=free |pmid=34930845 |pmc=8719853 |bibcode=2021PNAS..11813315B |language=en}}</ref>