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Carbon (IPA: ) is a chemical element in the periodic table that has the symbol C and atomic number 6. An abundant nonmetallic, tetravalent element, carbon has several allotropic forms.
Overview Carbon occurs in all organic life and is the basis of organic chemistry. This nonmetal also has the interesting chemical property of being able to bond with itself and a wide variety of other elements, forming nearly ten million known compounds. When united with oxygen it forms carbon dioxide, which is vital to plant growth. When united with hydrogen, it forms various compounds called hydrocarbons which are essential to industry in the form of fossil fuels. When combined with both oxygen and hydrogen it can form many groups of compounds including fatty acids, which are essential to life, and esters, which give flavor to many fruits. The isotope carbon-14 is commonly used in radioactive dating. Notable characteristics Carbon is a remarkable element for many reasons. Its different forms include the hardest naturally occurring substance (diamond) and one of the softest substances (graphite) known. Moreover, it has a great affinity for bonding with other small atoms, including other carbon atoms, and its small size makes it capable of forming multiple bonds. Because of these properties, carbon is known to form nearly ten million different compounds, the large majority of all chemical compounds. Carbon compounds form the basis of all life on Earth and the carbon-nitrogen cycle provides some of the energy produced by the Sun and other stars. Moreover, carbon has the highest melting/sublimation point of all elements. At atmospheric pressure it has no actual melting point as its triple point is at 10 MPa (100 bar) so it sublimates above 4000 K. Thus it remains solid at higher temperatures than the highest melting point metals like tungsten or rhenium, regardless of its allotropic form. Carbon was not created during the Big Bang due to the fact that it needs a triple collision of alpha particles (helium nuclei) to be produced. The universe initially expanded and cooled too fast for that to be possible. It is produced, however, in the interior of stars in the horizontal branch, where stars transform a helium core into carbon by means of the triple-alpha process. It was also created in a multi-atomic state. Applications Carbon is a very important component of all known living systems, and without it life as we know it could not exist (see alternative biochemistry). The major economic use of carbon is in the form of hydrocarbons, most notably the fossil fuel methane gas and crude oil (petroleum). Crude oil is used by the petrochemical industry to produce, amongst others, gasoline and kerosene, through a distillation process, in refineries. Crude oil forms the raw material for many synthetic substances, many of which are collectively called plastics. Other uses The chemical and structural properties of fullerenes, in the form of carbon nanotubes, has promising potential uses in the nascent field of nanotechnology. History and Etymology Carbon was discovered in prehistory and was known to the ancients, who manufactured it by burning organic material in insufficient oxygen (making charcoal). It is also found in abundance in the sun, stars, comets, and atmospheres of most planets. Carbon in the form of microscopic diamonds is found in some meteorites. Natural diamonds are found in kimberlite of ancient volcanic "pipes," found in South Africa, Arkansas, and elsewhere. Diamonds are now also being recovered from the ocean floor off the Cape of Good Hope. About 30% of all industrial diamonds used in the U.S. are now made synthetically. The energy of the sun and stars can be attributed at least in part to the well-known carbon-nitrogen cycle. The name of Carbon comes from Latin carbo, whence comes French charbone, meaning charcoal. In German and Dutch, the names for carbon are Kohlenstoff and koolstof respectively, both literally meaning "coal-stuff". Allotropes
Occurrence There are nearly ten million carbon compounds known to science. Many thousands of these are vital to life processes. They are also many organic-based reactions of economic importance. Carbon is abundant in the sun, stars, comets, and in the atmospheres of most planets. Some meteorites contain microscopic diamonds that were formed when the solar system was still a protoplanetary disk. In combination with other elements, carbon is found in the earth's atmosphere (around 810 gigatonnes) and dissolved in all water bodies (around 36000 gigatonnes). Around 1900 gigatonnes are present in the biosphere. Hydrocarbons (such as coal, petroleum, and natural gas) contain carbon as well--coal "reserves" (not "resources") amount to around 1000 gigatonnes, and oil reserves around 150 gigatonnes. With smaller amounts of calcium, magnesium, and iron, carbon is a major component of very large masses carbonate rock (limestone, dolomite, marble etc.). Graphite is found in large quantities in New York and Texas, the United States; Russia; Mexico; Greenland and India. Natural diamonds occur in the mineral kimberlite found in ancient volcanic "necks," or "pipes". Most diamond deposits are in Africa, notably in South Africa, Namibia, Botswana, the Republic of the Congo and Sierra Leone. There are also deposits in Arkansas, Canada, the Russian Arctic, Brazil and in Northern and Western Australia. Organic compounds The most prominent oxide of carbon is carbon dioxide, CO2. This is a minor component of the Earth's atmosphere, produced and used by living things, and a common volatile elsewhere. In water it forms trace amounts of carbonic acid, H2CO3, but as most compounds with multiple single-bonded oxygens on a single carbon it is unstable. Through this intermediate, though, resonance-stabilized carbonate ions are produced. Some important minerals are carbonates, notably calcite. Carbon disulfide, CS2, is similar. The other oxides are carbon monoxide, CO, the uncommon carbon suboxide, C3O2 and even carbon trioxide, CO3. Carbon monoxide is formed by incomplete combustion, and is a colorless, odorless gas. The molecules each contain a triple bond and are fairly polar, resulting in a tendency to bind permanently to hemoglobin molecules, so that the gas is highly poisonous. Cyanide, CN-, has a similar structure and behaves a lot like a halide ion; the nitride cyanogen, (CN)2, is related. With reactive metals, such as tungsten, carbon forms either carbides, C-, or acetylides, C22- to form alloys with very high melting points. These anions are also associated with methane and acetylene, both very weak acids. All in all, with an electronegativity of 2.5, carbon prefers to form covalent bonds. A few carbides are covalent lattices, like carborundum, SiC, which resembles diamond. Carbon chains Carbon has the ability to form long chains with interconnecting C-C bonds. This property is called catenation. Carbon-carbon bonds are fairly strong, and abnormally stable. This property is important as it allows carbon to form a huge number of compounds; in fact, there are more known carbon-containing compounds than all the compounds of the other chemical elements combined. The simplest form of an organic molecule is the hydrocarbon - a large family of organic molecules that, by definition, are composed of hydrogen atoms bonded to a chain of carbon atoms. Chain length, side chains and functional groups all affect the properties of organic molecules. Carbon cycle Under terrestrial conditions, conversion of one isotope to another is very rare. Therefore, for practical purposes, the amount of carbon on Earth is constant. Thus processes that use carbon must obtain it somewhere, dispose of it somewhere. The paths that carbon follows in the environment are called the carbon cycle. For example, plants draw carbon dioxide out of the environments and use it to build biomass as in carbon respiration. Some of this biomass is eaten by animals, where some of it is exhaled 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 become sedimentary rock, so forth. Isotopes Carbon has two stable, naturally-occurring isotopes: carbon-12, or 12C, (98.89%) and carbon-13, or 13C, (1.11%), and one unstable, naturally-occurring, radioisotope; carbon-14 or 14C. There are 15 known isotopes of carbon and the shortest-lived of these is 8C which decays through proton emission and alpha decay. It has a half-life of 1.98739x10-21 s. In 1961 the International Union of Pure and Applied Chemistry adopted the isotope carbon-12 as the basis for atomic weights. Carbon-14 has a half-life of 5730 y and has been used extensively for radiocarbon dating carbonaceous materials. The exotic 19C exhibits a Nuclear halo Precautions Carbon is relatively safe. Inhalation of fine soot in large quantities can be dangerous. Carbon may spawn flames at very high temperatures and burn vigorously and brightly (as in the Windscale fire). There are a tremendous number of carbon compounds; some are lethally poisonous (cyanide, CN-), and some are essential to life (glucose). See also | ||||||||||
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