Pengguna:Agung.karjono/Bak pasir/Karbon: Perbedaan antara revisi

{{Kotak info karbon}}

 

 

==Karakteristik==

 

Perbendaan bentuk atau ''[[alotropi]]'' karbon (lihat di bawah) meliputi salah satu bahan yang dikenal palilng lunak, [[grafit]], dan juga bahan terkeras yang terbentuk secara alami, [[intan]]. Selain itu, karbon mempunyai afinitas membentuk [[ikatan kimia|ikatan]] dengan atom kecil lainnya, termasuk atom karbon lainnya, dan mampu membentuk ikatan [[kovalen]] multi-stabil dengan atom-atom ini. Alhasil, karbon dikenal membentuk hampir sepuluh juta senyawa yang berbeda; mayoritas dari seluruh [[senyawa kimia]].<ref name=lanl/> Karbon juga mempunyai titik [[sublimasi (kimia)|sublimasi]] tertinggi di antara unsur-unsur kimia. Pada [[tekanan atmosfer]], karbon tidak memiliki titik lebur karena [[titik tripel|titik tripelnya]] adalah 10,8 ± 0,2&nbsp;MPa and 4.600 ± 300 K (~4.330&nbsp;°C or 7.820&nbsp;°F),<ref name=triple2/><ref name=triple3/> sehingga ia menyublim pada sekitar 3.900&nbsp;K.<ref name="triple">{{cite journal|journal=Nature|volume=276|pages=695–696|date=1978|doi=10.1038/276695a0|title=The controversial carbon solid−liquid−vapour triple point|first=A.|last=Greenville Whittaker|issue=5689|bibcode=1978Natur.276..695W }}</ref><ref>{{cite news|url=http://lbruno.home.cern.ch/lbruno/documents/Bibliography/LHC_Note_78.pdf|title=On Graphite Transformations at High Temperature and Pressure Induced by Absorption of the LHC Beam|first=J. M.|last=Zazula|date=1997|accessdate=2009-06-06|publisher=CERN}}</ref>

{{main|Alotrop karbon}}

[[Atom karbon]] adalah spesies dengan umur paling pendek dan, oleh sebab itu, karbon distabilkan dalam beragam struktur multi atom dengan konfigurasi molekul yang berbeda yang disebut [[alotrop]]. Tiga alotrop karbon yang relatif cukup dikenal adalah [[karbon amorf]], [[grafit]], dan [[intan]]. Setelah dianggap eksotis, [[fulerena]] yang saat ini sering disintesis dan digunakan dalam penelitian; mereka mulai mengungkap juga ''[[Bulkyball (molekul)|bulkyballs]]'',<ref name="buckyballs"/><ref name="nanotubes">{{cite book|editor=Ebbesen, T. W.|date=1997|title=Carbon nanotubes—preparation and properties|publisher=CRC Press|location=Boca Raton, Florida|isbn=0-8493-9602-6}}</ref> [[karbon nanotube]],<ref name="nanotubes2">{{cite journal|editor=Dresselhaus, M. S.|editor2= Dresselhaus, G.|editor3= Avouris, Ph.|date=2001|title=Carbon nanotubes: synthesis, structures, properties and applications|journal=Topics in Applied Physics|volume=80|isbn=3-540-41086-4|publisher=Springer|location=Berlin}}</ref> [[karbon nanobud]]<ref name="nanobuds">{{cite journal|date=2007|title=A novel hybrid carbon material|journal=Nature Nanotechnology|volume=2|pages=156–161|doi=10.1038/nnano.2007.37|last1=Nasibulin|first1=Albert G.|pmid=18654245|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.|issue=3|bibcode=2007NatNa...2..156N|display-authors=8 }}</ref> dan [[Karbon nanofiber|nanofiber]].<ref>{{cite journal|date=2007|title=Investigations of NanoBud formation|journal=Chemical Physics Letters|volume=446|pages=109–114|doi=10.1016/j.cplett.2007.08.050|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.|bibcode=2007CPL...446..109N }}</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|volume=274|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> Beberapa alotrop eksotis lainnya juga telah ditemukan, seperti [[lonsdaleit]],<ref name="lonsdaletite">{{cite journal|date=1967|title=Lonsdaleite, a new hexagonal polymorph of diamond|journal=Nature|volume=214|pages=587–589|doi=10.1038/214587a0|first=Frondel|last=Clifford|last2=Marvin|first2=Ursula B.|issue=5088|bibcode=1967Natur.214..587F }}</ref> ''[[glassy carbon]]'',<ref name="glassy carbon"/> [[karbon 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|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.|issue=7}}</ref> dan [[karbon asetilen linear]] (karbin) ({{lang-en|carbyne}}).<ref name=LAC>{{cite book|author=Heimann, Robert Bertram|author2=Evsyukov, Sergey E.|author3=Kavan, Ladislav|last-author-amp=yes|title=Carbyne and carbynoid structures|url=http://books.google.com/books?id=swSQZcTmo_4C&pg=PA1|accessdate=2011-06-06|date=28 February 1999|publisher=Springer|isbn=978-0-7923-5323-2|pages=1–}}</ref>

 

Bentuk [[amorf]] adalah campuran beragam atom karbon dalam bentuk non-kristal, iregular, kondisi glassy, yang secara esensi adalah [[grafit]] tetapi tidak mempertahankan struktur makro kristalnya. Karbon ini hadir dalam bentuk serbuk, dan merupakan konstituen utama dalam [[arang]], [[jelaga]], dan [[karbon aktif]]. Pada tekanan normal, karbon berada dalam bentuk [[grafit]], di mana masing-masing atom terikat secara trigonal dengan tiga atom karbon lainnya pada satu bidang cincin [[Heksagon|heksagonal]], seperti yang diperlihatkan oleh [[hidrokarbon aromatik]].<ref>{{cite book|title=The polymorphism of elements and compounds|last=Jenkins|first=Edgar|date=1973|publisher=Taylor & Francis|isbn=0-423-87500-0|page=30|url=http://books.google.com/books?id=XNYOAAAAQAAJ&pg=PA30|accessdate=2011-05-01}}</ref> Hasilnya adalah 2-dimensi datar yang tersusun dan terikat lemah melalui [[gaya van der Waals]].<!-- no evidence for upper case van der Waals; see [[Talk:Van der Waals#Van should be capitalized unless preceded by first name]] rebuttal -->Hal ini menyumbang sifat grafit yang lunak dan mudah patah.

 

 

 

 

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|volume=678|issue=1|date=March 26, 2004|author=Schewe, Phil|author2=Stein, Ben|last-author-amp=yes|journal=Physics News Update}}</ref> Similarly, [[glassy carbon]] contains a high proportion of closed [[porosity]],<ref name="glassy carbon"/> 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=LAC/> has the chemical structure<ref name="LAC"/> -(C:::C){{sub|n}}-. Carbon in this modification is linear with ''sp'' [[orbital hybridization]], and is a [[polymer]] with alternating single and triple bonds. This type of carbyne is of considerable interest to [[nanotechnology]] as its [[Young's modulus]] is forty times that of the hardest known material&nbsp;– diamond.<ref>{{cite journal|title=Harder than Diamond: Determining the Cross-Sectional Area and Young's Modulus of Molecular Rods|author=Itzhaki, Lior|doi=10.1002/anie.200502448|journal=Angew. Chem. Int. Ed.|date=2005|volume=44|last2=Altus|first2=Eli|last3=Basch|first3=Harold|last4=Hoz|first4=Shmaryahu|pmid=16240306|issue=45|pages=7432–5}}</ref>

Carbon is the [[Abundance of the chemical elements|fourth most abundant chemical element]] in the universe by mass after hydrogen, helium, and oxygen. Carbon is abundant in the [[Sun]], [[star]]s, [[comet]]s, and in the [[celestial body's atmosphere|atmospheres]] of most [[planet]]s.<ref name="NASA-20140221" /> Some [[meteorite]]s contain microscopic diamonds that were formed when the [[solar system]] was still a [[protoplanetary disk]]. Microscopic diamonds may also be formed by the intense pressure and high temperature at the sites of meteorite impacts.<ref>{{cite book|author=Mark, Kathleen|date=1987|title=Meteorite Craters|publisher=University of Arizona Press|isbn=0-8165-0902-6}}</ref>

 

 

It has been estimated that the solid earth as a whole contains 730 [[parts per million|ppm]] of carbon, with 2000 ppm in the core and 120 ppm in the combined mantle and crust.<ref>William F McDonough [http://quake.mit.edu/hilstgroup/CoreMantle/EarthCompo.pdf The composition of the Earth] in {{cite book|title=Earthquake Thermodynamics and Phase Transformation in the Earth's Interior|date=2000|isbn=978-0126851854}}</ref> Since the mass of the earth is {{val|5.972|e=24|u=kg}}, this would imply 4360 million [[gigatonne]]s of carbon. This is much more than the amounts in the oceans or atmosphere (below).

[[Isotope]]s of carbon are [[atomic nucleus|atomic nuclei]] that contain six [[proton]]s plus a number of [[neutron]]s (varying from 2 to 16). Carbon has two stable, naturally occurring [[isotope]]s.<ref name="isotopes"/> The isotope [[carbon-12]] ({{sup|12}}C) forms 98.93% of the carbon on Earth, while [[carbon-13]] ({{sup|13}}C) forms the remaining 1.07%.<ref name="isotopes"/> The concentration of {{sup|12}}C is further increased in biological materials because biochemical reactions discriminate against {{sup|13}}C.<ref>{{cite journal|last=Gannes|first=Leonard Z.|last2=Del Rio|first2=Carlos Martı́nez|last3=Koch|first3=Paul|title=Natural Abundance Variations in Stable Isotopes and their Potential Uses in Animal Physiological Ecology|journal=Comparative Biochemistry and Physiology&nbsp;– Part A: Molecular & Integrative Physiology|volume=119|issue=3|pages=725–737|date=1998|doi=10.1016/S1095-6433(98)01016-2}}</ref> In 1961, the [[International Union of Pure and Applied Chemistry]] (IUPAC) adopted the isotope [[carbon-12]] as the basis for [[atomic weight]]s.<ref>{{cite web|url=http://www.bipm.org/en/si/base_units/|title=Official SI Unit definitions|accessdate=2007-12-21}}</ref> Identification of carbon in [[NMR]] experiments is done with the isotope {{sup|13}}C.

 

 

There are 15 known isotopes of carbon and the shortest-lived of these is {{sup|8}}C which decays through [[proton emission]] and [[alpha decay]] and has a half-life of 1.98739x10{{sup|−21}} [[Second|s]].<ref>{{cite web|url=http://barwinski.net/isotopes/query_select.php|title=Use query for carbon-8|accessdate=2007-12-21|publisher=barwinski.net}}</ref> The exotic {{sup|19}}C exhibits a [[nuclear halo]], which means its [[radius]] is appreciably larger than would be expected if the [[Atomic nucleus|nucleus]] were a [[sphere]] of constant [[density]].<ref>{{cite journal|url=http://www.sciencemag.org/cgi/content/full/286/5437/28?ck=nck|title=Beaming Into the Dark Corners of the Nuclear Kitchen|doi=10.1126/science.286.5437.28|pages=28–31|date=1999|last1=Watson|first1=A.|journal=Science|volume=286|issue=5437}}</ref>

===Formation in stars===

{{main|Triple-alpha process|CNO cycle}}

 

Rotational transitions of various isotopic forms of carbon monoxide (for example, {{sup|12}}CO, {{sup|13}}CO, and C{{sup|18}}O) are detectable in the [[submillimetre astronomy|submillimeter]] wavelength range, and are used in the study of [[Star formation|newly forming stars]] in [[molecular clouds]].<ref>{{cite book|author=Pikelʹner, Solomon Borisovich|title=Star formation|url=http://books.google.com/books?id=qbGLgcxnfpIC&pg=PA38|accessdate=2011-06-06|date=1977|publisher=Springer|isbn=978-90-277-0796-3|pages=38–}}</ref>