Editing Period 2 element (section)

===Carbon===
{{main article|Carbon}}
[[File:Diamond-and-graphite-with-scale.jpg|thumb|left|150px|Diamond and graphite, two different [[allotrope]]s of carbon]]

Carbon is the chemical element with atomic number 6, occurring as <sup>12</sup>C, <sup>13</sup>C and <sup>14</sup>C.<ref name=wec>[http://www.webelements.com/carbon/ Carbon] at WebElements.</ref> At standard temperature and pressure, carbon is a solid, occurring in [[Allotropes of carbon|many different allotropes]], the most common of which are [[graphite]], [[diamond]], the [[fullerenes]] and [[amorphous carbon]].<ref name=wec/> Graphite is a soft, [[hexagonal crystal system|hexagonal crystalline]], opaque black [[semimetal]] with very good [[electrical conductor|conductive]] and [[thermodynamic equilibrium|thermodynamically stable]] properties. Diamond however is a highly [[transparency (optics)|transparent]] [[Transparency and translucency|colourless]] [[cubic crystal system|cubic crystal]] with poor conductive properties, is the [[Mohs scale of mineral hardness|hardest known naturally occurring mineral]] and has the highest [[refractive index]] of all [[gemstones]]. In contrast to the [[crystal lattice]] structure of diamond and graphite, the [[fullerenes]] are [[molecules]], named after [[Richard Buckminster Fuller]] whose architecture the molecules resemble. There are several different fullerenes, the most widely known being the "buckeyball" C<sub>60</sub>. Little is known about the fullerenes and they are a current subject of research.<ref name=wec/> There is also amorphous carbon, which is carbon without any crystalline structure.<ref>{{cite book |chapter=Amorphous carbon |chapter-url=http://iupac.org/goldbook/A00294.html |title=IUPAC Compendium of Chemical Terminology |publisher=International Union of Pure and Applied Chemistry |year=1997|edition=2nd |access-date=2008-09-24}}</ref> In [[mineralogy]], the term is used to refer to [[soot]] and [[coal]], although these are not truly amorphous as they contain small amounts of graphite or diamond.<ref>{{cite journal |url=http://gltrs.grc.nasa.gov/reports/1996/CR-198469.html |format=PDF |title=Soot Precursor Material: Spatial Location via Simultaneous LIF-LII Imaging and Characterization via TEM |journal=NASA Contractor Report |last=Vander Wal |first=R. |issue=198469 |date=May 1996 |access-date=2008-09-24 }}{{dead link|date=June 2021|bot=medic}}{{cbignore|bot=medic}}</ref><ref>{{cite book |chapter=diamond-like carbon films |chapter-url=https://goldbook.iupac.org/terms/view/D01673 |title=IUPAC Compendium of Chemical Terminology |publisher=International Union of Pure and Applied Chemistry |year=1997|edition=2nd |doi=10.1351/goldbook.D01673 |access-date=2008-09-24}}</ref> Carbon's most common isotope at 98.9% is <sup>12</sup>C, with six protons and six neutrons.<ref name=slide>[http://www.scienceschool.usyd.edu.au/media/17-dasgupta-slides.pdf Presentation about isotopes] {{webarchive|url=https://web.archive.org/web/20080719061754/http://www.scienceschool.usyd.edu.au/media/17-dasgupta-slides.pdf |date=2008-07-19 }} by Mahananda Dasgupta of the Department of Nuclear Physics at Australian National University.</ref> <sup>13</sup>C is also stable, with six protons and seven neutrons, at 1.1%.<ref name=slide/> Trace amounts of <sup>14</sup>C also occur naturally but this [[radioisotope|isotope is radioactive]] and decays with a half life of 5730 years; it is used for [[radiocarbon dating]].<ref>{{cite journal |last=Plastino |first=W. |author2=Kaihola, L. |author3=Bartolomei, P. |author4=Bella, F. |year=2001 |title=Cosmic Background Reduction In The Radiocarbon Measurement By Scintillation Spectrometry At The Underground Laboratory Of Gran Sasso |journal=Radiocarbon |volume=43 |issue=2A |pages=157–161 |doi=10.1017/S0033822200037954 |doi-access=free }}</ref> Other [[isotopes of carbon]] have also been synthesised. Carbon forms covalent bonds with other non-metals with an oxidation state of −4, −2, +2 or +4.<ref name=wec/>

Carbon is the fourth most abundant element in the universe by mass after [[hydrogen]], [[helium]] and oxygen<ref>[http://plymouthlibrary.org/faqelements.htm Ten most abundant elements in the universe, taken from ''The Top 10 of Everything'', 2006, Russell Ash, page 10. Retrieved October 15, 2008.] {{webarchive|url=https://web.archive.org/web/20100210170504/http://plymouthlibrary.org/faqelements.htm |date=February 10, 2010 }}</ref> and is the second [[Chemical makeup of the human body|most abundant element in the human body]] by mass after oxygen,<ref>{{cite book
 | last = Chang
 | first = Raymond
 | title = Chemistry, Ninth Edition
 | publisher = McGraw-Hill
 | year = 2007
 | pages = 52
 | isbn = 978-0-07-110595-8 }}</ref> the third most abundant by number of atoms.<ref name="Freitas">{{cite book |first=Robert A. Jr. |last=Freitas |title=Nanomedicine |url=http://www.foresight.org/Nanomedicine/Ch03_1.html |publisher=Landes Bioscience |year=1999 |page=Tables 3–1 & 3–2 |isbn=1-57059-680-8 |no-pp=true }}</ref> There are an almost infinite number of compounds that contain carbon due to carbon's ability to form long stable chains of C&nbsp;— C bonds.<ref name="hydrocarbon"/><ref name=acell>{{cite book |last = Alberts |first = Bruce|author2=Alexander Johnson |author3=Julian Lewis |author4=Martin Raff |author5=Keith Roberts |author6=Peter Walter  |title = Molecular Biology of the Cell | chapter=The Chemical Components of a Cell |publisher = Garland Science |url = https://www.ncbi.nlm.nih.gov/books/bv.fcgi?highlight=carbon&rid=mboc4.section.165|year = 2002}}</ref> The simplest carbon-containing molecules are the [[hydrocarbon]]s, which contain carbon and hydrogen,<ref name="hydrocarbon"/> although they sometimes contain other elements in [[functional group]]s. Hydrocarbons are used as [[fossil fuels]] and to manufacture [[plastics]] and [[petrochemicals]]. All [[organic compound]]s, those essential for life, contain at least one atom of carbon.<ref name="hydrocarbon">{{cite web| title = Structure and Nomenclature of Hydrocarbons | publisher = Purdue University| url = http://chemed.chem.purdue.edu/genchem/topicreview/bp/1organic/organic.html| access-date = 2008-03-23}}</ref><ref name=acell/> When combined with oxygen and hydrogen, carbon can form many groups of important biological compounds<ref name=acell/> including [[sugar]]s, [[lignan]]s, [[chitin]]s, [[Alcohol (chemistry)|alcohol]]s, [[fat]]s, and aromatic [[ester]]s, [[carotenoids]] and [[terpenes]]. With [[nitrogen]] it forms [[alkaloid]]s, and with the addition of sulfur also it forms [[antibiotic]]s, [[amino acid]]s, and [[rubber]] products. With the addition of phosphorus to these other elements, it forms [[DNA]] and [[RNA]], the chemical-code carriers of life, and [[adenosine triphosphate]] (ATP), the most important energy-transfer molecule in all living cells.<ref name=acell/>