Kárbọ̀nù

Kárbọ̀nù(látiLátìnì:carbo"èédú") jeipilese kemikato niami-idamoCatinomba atomu6. Gẹ́gẹ́ bí ìkan nínúẹgbẹ́ 14lórítábìlì ìdásìkò àwọn ẹ́límẹ̀ntì, ó jẹ́aláìjẹ́-mẹ́tàlìàtiafagbáramẹ́rindìmú—èyí jẹ́ pé ẹ̀lẹ́ktrọ́nù mẹ́rin wà láti dá ìsopọ̀ kẹ́míkààjọfagbáradìmú. Àwọnísótòpùkárbọ̀nù mẹ́ta ni wọ́n wà fún ra wọn,CàtiCjẹ́ dídúró, nígbàtíCjẹ́onítítànyindin, tóúntúká díẹ̀díẹ̀ pẹ̀lúàsìkò àbọ̀-ìgbéayétó tó bíi ọdún 5,730.Kárbọ̀nù ni ìkan nínú àwọn ẹ́límẹ̀ntì díẹ̀ tí wọ́n ti jẹ́ dídámọ̀ láti ìgbà àtijọ́.
Orísiàwọn álótrópù kárbọ̀nùlọ́wà tí èyí tó gbajúmọ̀ nínú wọn jẹ́gráfáìt,díámọ́ndì, àtikárbọ̀nù àìlétòara.Àwọnìní oníṣeẹ̀dákárbọ̀nù yàtọ̀ gẹ́gẹ́bí irú álótrópù bá ṣe rí. Fún àpẹrẹ, díámọ́ndì jẹ́híhannú, nígbàtí gráfáìt jẹ́dídinútó sì dúdú. Díámọ́ndì jẹ́ ìkan nínú àwọn èròjà tó le jùlọ, nígbàtí gráfáìt jẹ́ dídẹra dáadáa tó bẹ̀ẹ̀ láti fi kọ ìwé. Díámọ́ndì níìgbéwọra oníṣetannátó kéré gidi, nígbàtí gráfáìt jẹ́olùgbéwọrató dára gidigidi. Lábẹ́ àwọn ìṣẹ̀lẹ̀ onídéédé, díámọ́ndì,nánótúbù kárbọ̀nùàtigrafínnìníìgbéwọra onígbígbónátó gajùlọ ní àrinàwọn èròjà tí a mọ̀.
Gbogbo àwọn álótrópù kárbọ̀nù jẹ́ aláralíle ní abẹ́ ìṣẹ̀lẹ̀ onídéédé tí gráfáìt jẹ́ irú èyí tó jẹ́ dídúró jùlọníagbára onítigbígbóná. Wọ́n jẹ́ olódì sí kẹ́míkà bẹ́èsìni wọ́n fẹ́ ìgbónásí gíga láti túndaramọ́ra gan mọ́ ọ́ksíjìn. The most commonIpòàyè ìsọdiọ̀ksídìkárbọ̀nù nínú àwọnàdàpọ̀ aláìníọ́rgánìni +4, nígbàtí +2 wà nínúmónọ́ksídì kárbọ̀nùàti àwọnmetali irekojakarbonilimiran. Orisun totobijulo karbonu alainiorgani niokuta-efun,dolomaitiatidioksidi karbonu, sugbon opo re tun wa ninu awon ìwalẹ̀ oniorganièédú,peat,epo petroliomuatiklatarati methani. Karbonu se Carbon forms moreadapoju awon elimenti yiowu lo, bi milionu mewaadapo oniorganiogidi lo wa titi doni, sibe awon yi ko ju ida die lo ninu gbogbo iye iru adapo karbonu to se e se labe isele onideede.
Karbonu ni elimenti 15kto gbalejuloni inu iwule Aye, atielimenti kerin to gbale julo ninu agbala-aye gegebi iye akojoleyinháídrójìn,hílíọ̀mù, atiọ́ksíjìn. O wa ninu gbogbo iru eda ohun alaye, be sini ninu ara eniyan karbonu ni elimenti keji to gbalejulo gegebi iye akojo (bi 18.5%) leyin oksijin.Igbale yi, lapapo mo ipinsorisirisi awonadapo organikiati agbara won lati da polimeri ni ibi igbonasi to wopo ni ileAye, so elimenti yi di ipile kemika gbogbo ohun elemi.
Àwọn orísi ìdá tàbíálótrópùkárbọ̀nù (ẹ wo ìsàlẹ̀) ní nínú wọn ohun tó le jùlọ ní ìdáyé,díámọ̀ndì, àti èyi tó jẹ́ ìkan nínú ohun rírọ̀ jùlọ,gráfáìtì. Bákannáà, ó ní ìfẹ́ fúnìsopọ̀mọ́ àwọnátọ̀mùkékeré míràn, bíi àwọn átọ̀mù kárbọ̀nù míràn, ó sí le dá ọ̀pọ̀ìsopọ̀ àjọfagbáradìmúafẹsẹ̀múlẹ̀ mọ́ àwọn átọ̀mú báyìí. Nítorí ẹ̀yí, kárbọ̀nù le dá orísirísi àdàpọ̀ tó pọ̀ tó mílíọ́mù mẹ́ẹ̀wá; ogunlọ́gọ̀ gbogbo àwọnàdápọ̀ kẹ́míkà.Carbon also has the highestsublimationpoint of all elements. Atatmospheric pressureit has no melting point as itstriple pointis at 10.8 ± 0.2 MPa and 4,600 ± 300 K (~4,330 °C or 7,820 °F),so it sublimates at about 3,900 K.
Carbon sublimes in a carbon arc which has a temperature of about 5,800 K (5,530 °C; 9,980 °F). Thus, irrespective of its allotropic form, carbon remains solid at higher temperatures than the highest melting point metals such astungstenorrhenium. Although thermodynamically prone to oxidation, carbon resists oxidation more effectively than elements such as iron and copper that are weaker reducing agents at room temperature.
Carbon compounds form the basis of all known life onEarth, and thecarbon-nitrogen cycleprovides some of the energy produced by theSunand other stars. Although it forms an extraordinary variety of compounds, most forms of carbon are comparatively unreactive under normal conditions. At standard temperature and pressure, it resists all but the strongest oxidizers. It does not react withsulfuric acid,hydrochloric acid,chlorineor any alkalis. At elevated temperatures carbon reacts with oxygen to form carbon oxides, and will reduce such metal oxides as iron oxide to the metal. Thisexothermicreaction is used in the iron and steel industry to control the carbon content of steel:
withsulfurto formcarbon disulfideand with steam in the coal-gas reaction:
Carbon combines with some metals at high temperatures to form metallic carbides, such as the iron carbidecementitein steel, andtungsten carbide, widely used as anabrasiveand for making hard tips for cutting tools.
As of 2009,grapheneappears to be the strongest material ever tested.However, the process of separating it fromgraphitewill require some technological development before it is economical enough to be used in industrial processes.
The system of carbon allotropes spans a range of extremes:
Atomic carbonis a very short-lived species and, therefore, carbon is stabilized in various multi-atomic structures with different molecular configurations calledallotropes. The three relatively well-known allotropes of carbon areamorphous carbon,graphite, anddiamond. Once considered exotic,fullerenesare nowadays commonly synthesized and used in research; they includebuckyballs,carbon nanotubes,carbon nanobudsandnanofibers.Several other exotic allotropes have also been discovered, such aslonsdaleite,glassy carbon,carbon nanofoamandlinear acetylenic carbon(carbyne).
Theamorphousform is an assortment of carbon atoms in a non-crystalline, irregular, glassy state, which is essentiallygraphitebut not held in a crystalline macrostructure. It is present as a powder, and is the main constituent of substances such ascharcoal,lampblack(soot) andactivated carbon. At normal pressures carbon takes the form ofgraphite, in which each atom is bonded trigonally to three others in a plane composed of fusedhexagonalrings, just like those inaromatic hydrocarbons.The resulting network is 2-dimensional, and the resulting flat sheets are stacked and loosely bonded through weakvan der Waals forces. This gives graphite its softness and itscleavingproperties (the sheets slip easily past one another). Because of the delocalization of one of the outer electrons of each atom to form aπ-cloud, graphite conductselectricity, but only in the plane of eachcovalently bondedsheet. This results in a lower bulkelectrical conductivityfor carbon than for mostmetals. The delocalization also accounts for the energetic stability of graphite over diamond at room temperature.
At very high pressures carbon forms the more compact allotropediamond, having nearly twice the density of graphite. Here, each atom is bondedtetrahedrallyto four others, thus making a 3-dimensional network of puckered six-membered rings of atoms. Diamond has the samecubic structureassiliconandgermaniumand because of the strength of the carbon-carbonbonds, it is the hardest naturally occurring substancein terms of resistance to scratching. Contrary to the popular belief that"diamonds are forever", they are in fact thermodynamically unstable under normal conditions and transform intographite.However, due to a high activation energy barrier, the transition into graphite is so extremely slow at room temperature as to be unnoticeable. Under some conditions, carbon crystallizes aslonsdaleite. This form has ahexagonalcrystallattice where all atoms are covalently bonded. Therefore, all properties of lonsdaleite are close to those of diamond.
Fullereneshave a graphite-like structure, but instead of purelyhexagonalpacking, they also contain pentagons (or even heptagons) of carbon atoms, which bend the sheet into spheres, ellipses or cylinders. The properties of fullerenes (split intobuckyballs,buckytubesandnanobuds) have not yet been fully analyzed and represent an intense area of research innanomaterials. The names"fullerene"and"buckyball"are given afterRichard Buckminster Fuller, popularizer ofgeodesic domes, which resemble the structure of fullerenes. The buckyballs are fairly large molecules formed completely of carbon bonded trigonally, formingspheroids(the best-known and simplest is the soccerball-shaped C60buckminsterfullerene).Carbon nanotubes are structurally similar to buckyballs, except that each atom is bonded trigonally in a curved sheet that forms a hollowcylinder.Nanobuds were first reported in 2007 and are hybrid bucky tube/buckyball materials (buckyballs are covalently bonded to the outer wall of a nanotube) that combine the properties of both in a single structure.
Of the other discovered allotropes,carbon nanofoamis aferromagneticallotrope 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 kg/m.Similarly,glassy carboncontains a high proportion of closedporosity,but contrary to normal graphite, the graphitic layers are not stacked like pages in a book, but have a more random arrangement.Linear acetylenic carbonhas the chemical structure-(C:::C)n-. Carbon in this modification is linear withsporbital hybridization, and is apolymerwith alternating single and triple bonds. This type of carbyne is of considerable interest tonanotechnologyas itsYoung's modulusis forty times that of the hardest known material – diamond.
Carbon is thefourth most abundant chemical elementin the universe by mass after hydrogen, helium, and oxygen. Carbon is abundant in theSun,stars,comets, and in theatmospheresof mostplanets. Somemeteoritescontain microscopic diamonds that were formed when thesolar systemwas still aprotoplanetary disk. Microscopic diamonds may also be formed by the intense pressure and high temperature at the sites of meteorite impacts.
In combination withoxygenincarbon dioxide, carbon is found in the Earth's atmosphere (approximately 810gigatonnesof carbon) and dissolved in all water bodies (approximately 36,000 gigatonnes of carbon). Around 1,900 gigatonnes of carbon are present in thebiosphere.Hydrocarbons(such ascoal,petroleum, andnatural gas) contain carbon as well—coal"reserves" (not "resources")amount to around 900 gigatonnes, andoil reservesaround 150 gigatonnes. Proven sources of natural gas are about 175 10cubic metres (representing about 105 gigatonnes carbon), but it is estimated that there are also about 900 10cubic metres of "unconventional" gas such asshale gas, representing about 540 gigatonnes of carbon.(In the past, quantities of hydrocarbons were greater. In the period from 1751 to 2008 about 347 gigatonnes of carbon were released as carbon dioxide to the atmosphere from burning of fossil fuels.)		
Carbon is also locked up asmethaneandmethane hydratesin polar regions. It is estimated that at least 1,400Gtof carbon is in this form just in (and under) the submarinepermafrostof theSiberian Shelf.
Carbon is a major component in very large masses ofcarbonaterock (limestone,dolomite,marbleand so on).Coalis the largest commercial source of mineral carbon, accounting for 4,000 gigatonnes or 80% of fossil carbon fuel.It is also rich in carbon – for example,anthracitecontains 92–98%.
As for individual carbon allotropes, graphite is found in large quantities in theUnited States(mostly inNew YorkandTexas),Russia,Mexico,Greenland, andIndia. Natural diamonds occur in the rockkimberlite, found in ancientvolcanic"necks", or "pipes". Most diamond deposits are inAfrica, notably inSouth Africa,Namibia,Botswana, theRepublic of the Congo, andSierra Leone. There are also deposits inArkansas,Canada, the RussianArctic,Braziland in Northern and WesternAustralia. Diamonds are now also being recovered from the ocean floor off theCape of Good Hope. However, though diamonds are found naturally, about 30% of all industrial diamonds used in the U.S. are now made synthetically.
Carbon-14 is formed in upper layers of the troposphere and the stratosphere, at altitudes of 9–15 km, by a reaction that is precipitated bycosmic rays.Thermal neutronsare produced that collide with the nuclei of nitrogen-14, forming carbon-14 and a proton.
Isotopesof carbon areatomic nucleithat contain sixprotonsplus a number ofneutrons(varying from 2 to 16). Carbon has two stable, naturally occurringisotopes.The isotopecarbon-12(C) forms 98.93% of the carbon on Earth, whilecarbon-13(C) forms the remaining 1.07%.The concentration ofC is further increased in biological materials because biochemical reactions discriminate againstC.In 1961, theInternational Union of Pure and Applied Chemistry(IUPAC) adopted the isotopecarbon-12as the basis foratomic weights.Identification of carbon inNMRexperiments is done with the isotopeC.
Carbon-14(C) is a naturally occurringradioisotopewhich occurs in trace amounts on Earth of up to 1 part pertrillion(0.0000000001%), mostly confined to the atmosphere and superficial deposits, particularly ofpeatand other organic materials.This isotope decays by 0.158 MeVβemission. Because of its relatively shorthalf-lifeof 5730 years,C is virtually absent in ancient rocks, but is created in theupper atmosphere(lowerstratosphereand uppertroposphere) by interaction ofnitrogenwithcosmic rays.The abundance ofC in theatmosphereand in living organisms is almost constant, but decreases predictably in their bodies after death. This principle is used inradiocarbon dating, invented in 1949, which has been used extensively to determine the age of carbonaceous materials with ages up to about 40,000 years.
There are 15 known isotopes of carbon and the shortest-lived of these isC which decays throughproton emissionandalpha decayand has a half-life of 1.98739x10s.The exoticC exhibits anuclear halo, which means itsradiusis appreciably larger than would be expected if thenucleuswere asphereof constantdensity.
Formation of the carbon atomic nucleus requires a nearly simultaneous triple collision ofalpha particles(heliumnuclei) within the core of agiantorsupergiantstar which is known as thetriple-alpha process, as the products of further nuclear fusion reactions of helium with hydrogen or another helium nucleus producelithium-5andberyllium-8respectively, both of which are highly unstable and decay almost instantly back into smaller nuclei.This happens in conditions of temperatures over 100 megakelvin and helium concentration that the rapid expansion and cooling of the early universe prohibited, and therefore no significant carbon was created during theBig Bang. Instead, the interiors of stars in thehorizontal branchtransform three helium nuclei into carbon by means of thistriple-alpha process.In order to be available for formation of life as we know it, this carbon must then later be scattered into space as dust, insupernovaexplosions, as part of the material which later forms second, third-generation star systems which have planets accreted from such dust.TheSolar Systemis one suchthird-generation starsystem. Another of the fusion mechanisms powering stars is theCNO cycle, in which carbon acts as acatalystto allow the reaction to proceed.
Rotational transitions of various isotopic forms of carbon monoxide (for example,CO,CO, and CO) are detectable in thesubmillimeterwavelength range, and are used in the study ofnewly forming starsinmolecular clouds.
Under terrestrial conditions, conversion of one element to another is very rare. Therefore, the amount of carbon on Earth is effectively constant. Thus, processes that use carbon must obtain it somewhere and dispose of it somewhere else. The paths that carbon follows in the environment make up thecarbon cycle. For example, plants drawcarbon dioxideout of their environment and use it to build biomass, as incarbon respirationor theCalvin cycle, a process ofcarbon fixation. Some of this biomass is eaten by animals, whereas some carbon is exhaled by animals as carbon dioxide. The carbon cycle is considerably more complicated than this short loop; for example, some carbon dioxide is dissolved in the oceans; dead plant or animal matter may becomepetroleumorcoal, which can burn with the release of carbon, should bacteria not consume it.