CARBON

Carbon is a chemical element that has the symbol C and atomic number 6. An abundant nonmetallic, tetravalent element, carbon has several allotropic forms.

The abundance of carbon in the universe, along with the unusual polymer-forming ability of carbon-based compounds at the common temperatures encountered on Earth, make this element the basis of the chemistry of all known life.
The name "carbon" comes from Latin language carbo, coal. In some Romance languages, the word can refer both to the element and to coal.

As the free element it forms allotropes from differing kinds of carbon-carbon bonds, such as in graphite and diamond. Coal is the main source of carbon in mineral form, containing up to 95% of carbon in anthracite. Recently discovered nanostructured forms called fullerenes include buckyballs such as C60, nanotubes, and nanofibers. Because of their high strength-to-weight ratio, it is hoped that many of these carbon compounds will soon be practical for use in advanced structural composite materials.
Not only can carbon also bond with itself, but it can also form chains with a wide variety of other elements, forming nearly ten million known compounds.
Carbon-containing polymers, often with oxygen and nitrogen atoms included at regular intervals in the main polymer chain, form the basis of nearly all industrial commercial plastics.

Carbon occurs in all organic life and is the basis of organic chemistry. When united with oxygen, carbon forms carbon dioxide, which is the main carbon source for plant growth. When united with hydrogen, it forms various flammable compounds called hydrocarbons which are essential to industry in the form of fossil fuels, and also other important living plant components like carotenoids and terpenes. When combined with oxygen and hydrogen, carbon can form many groups of important biological compounds including sugars, celluloses, lignans, chitins, alcohols, fats, and aromatic esters. With nitrogen it forms alkaloids, and with the addition of sulfur also it forms antibiotics, amino acids and proteins. With the addition of phosphorus to these other elements, it forms DNA and RNA, the chemical codes of life.

Carbon exhibits remarkable properties, some paradoxical. 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 is capable of forming multiple stable covalent bonds with such atoms. 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 atmospheri 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, irrespective of its allotropic form. Although thermodynamically prone to oxidation, it resists oxidation more effectively than some elements (like iron and even copper)that are weaker reducing agents at room temperature.

Although it forms an incredible 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 (such as fluorine and nitric acid). It does not react with sulfuric acid, hydrochloric acid, chlorine or any alkalis. At elevated temperatures it of course reacts with oxygen in flames and with sulfur vapors; it also combines with some metals at high temperatures to form metallic carbides and reduces such metal oxides as iron oxide.
Formation of the carbon atomic nucleus requires a nearly simultaneous triple collision of alpha particles (helium nuclei). This happens in temperature and helium concentration conditions that the rapid expansion and cooling of the early universe prohibited, and therefore no significant carbon was created during the Big Bang. Instead, the interiors of stars in the horizontal branch transform three helium nuclei into carbon by means of this triple-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, in supernovae explosions, as part of the material which later forms second-generation star systems which have planets accreted from such dust. The solar system is one such second-generation star, made from carbon in the dust of dozens of supernovae in its local area of the galaxy.

Carbon is essential to all known living systems, and without it life as we know it could not exist (see alternative biochemistry). The major economic use of carbon not in living or formerly-living material (such as food and wood) 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 isotope carbon-14 was discovered on February 27, 1940 and is used in radiocarbon dating.
Industrial diamonds are used in cutting, drilling, and polishing technologies.
Graphite is combined with clays to form the 'lead' used in pencils. It is also used as a lubricant and a pigment.
Diamond is used for decorative purposes, and also as drill bits and other applications making use of its hardness.
Carbon (usually as coke) is used to reduce iron ore into iron.
Carbon is added to iron to make steel.
Carbon is used as a neutron moderator in nuclear reactors.
Carbon fiber, which is mainly used for composite materials, as well as high-temperature gas filtration.
Carbon black is used as a filler in rubber and plastic compounds.
Graphite carbon in a powdered, caked form is used as charcoal for grilling, artwork and other uses.
Activated charcoal is used in medicine (as powder or compounded in tablets or capsules) to absorb toxins, poisons, or gases from the digestive system.
Carbon, due to its non-reactivity with many substances that corrode most materials, is often used as an electrode.
Carbon is the most commonly used element in nanotubes.
Rotational transitions of various isotopic forms of carbon monoxide (e.g. 12CO, 13CO, and 18CO) are detectable in the submillimeter regime, and are used in the study of newly forming stars in molecular clouds.
The chemical and structural properties of fullerenes, in the form of carbon nanotubes, has promising potential uses in the nascent field of nanotechnology.