1s² 2s²p²

History

It 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 carbon-nitrogen cycle.

The name of Carbon comes from Latin carbo, whence comes French charbon, meaning charcoal.  In German and Dutch, the names for carbon are Kohlenstoff and koolstof respectively, both literally meaning coal-stuff.

Characteristics

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 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, irrespective of its allotropic form.

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, Chlorine or any alkalis.  At elevated temperatures it of course reacts with oxygen in flames.

Because its formation requires a triple collision of alpha particles (Helium nuclei) that the rapid expansion and cooling of the universe prohibited, Carbon was not created during the Big Bang.  The universe initially expanded and cooled too fast for that to be possible.  The interiors of stars in the horizontal branch transform a Helium core into Carbon by means of the 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 forms second-generation star systems with planets accreted from such dust.

As the free element it forms allotropes from differing kinds of Carbon-Carbon bonds, such as graphite, coal, and diamond.  Recently discovered geometric forms include fullerenes and nanotubes.  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, CO₂, 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.

Occurrence

Carbon is the fourth most abundant chemical element in the universe by mass, after Hydrogen, Helium, and Oxygen.  Carbon is abundant in the sun, stars, comets, and in the atmospher 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 gigatons) 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 gigatons, and oil reserves around 150 gigatons.  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; 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.

According to studies from the Massachusetts Institute of Technology, an estimate of the global carbon budget is:

Applications

Carbon is a essential to all known living systems, and without it life as we know it could not exist.  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, CH₄,  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.

• The isotope Carbon-14 was discovered on February 27, 1940 and is used in radiocarabon dating. 
• Industrial Diamonds are used in the boring industry.
• 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.

The chemical and structural properties of fullerenes, in the form of Carbon nanotubes, has promising potential uses in the nascent field of nanotechnology.

Allotropes

The allotropes of Carbon are the different molecular configurations that pure Carbon can take.

The three relatively well-known allotropes of Carbon are amorphous carbon, graphite, and diamond.  Several exotic allotropes have also been synthesized or discovered, including fullerences, carbon nanotubes, lonsdaleite and aggregated diamond nanorods.

In its amorphous form, Carbon is essentially graphite but not held in a crystalline macrostructure.  It is, rather, present as a powder which is the main constituent of substances such as charcoal, lampblack (soot) and activated  Carbon.

Basic phase diagram of Carbon, which shows the state of matter for varying temperatures and pressures.  The hashed regions indicate conditions under which one phase is metastable, so that two phases can coexist.

At normal pressures carbon takes the form of graphite, in which each atom is bonded to three others in a plane composed of fused hexagonal rings, just like those in aromatic hydrocarbons.  The two known forms of graphite, alpha (hexagonal) and beta (rhombohedral), both have identical physical properties, except for their crystal structure.  Graphites that naturally occur have been found to contain up to 30% of the beta form, when synthetically-produced graphite only contains the alpha form.   The alpha form can be converted to the beta form through mechanical treatment and the beta form reverts to the alpha form when it is heated above 1000°C.

Because of the delocalization of the pi-cloud, graphite conducts electricity.  The material is soft and the sheets, frequently separated by other atoms, are held together only by Van der Waals forces, so easily slip past one another.

At very high pressures carbon forms an allotrope called diamond, in which each atom is bonded to four others.  Diamond has the same cubic structure as Silicon and Germanium and, thanks to the strength of the Carbon-Carbon bonds, is together with the isoelectronic Boron Nitride (BN) the hardest substance in terms of resistance to scratching.  The transition to graphite at room temperature is so slow as to be unnoticeable. Under some conditions, carbon crystallizes as Lonsdaleite, a form similar to diamond but hexagonal.

Fullerenes have a graphite-like structure, but instead of purely hexagonal packing, also contain pentagons (or possibly heptagons) of Carbon atoms, which bend the sheet into spheres, ellipses or cylinders.  The properties of fullerenes (also called "Buckyballs" and "Buckytubes") have not yet been fully analyzed.   All the names of fullerenes are after Buckminster Fuller, developer of the geodesic dome, which mimics the structure of "buckyballs".

A nanofoam allotrope has been discovered which is ferromagnetic.

Eight allotropes of carbon: Diamond, graphite, lonsdaleite, C60, C540, C70, amorphous carbon and a carbon nanotube.

Carbon allotropes include:

• Diamond: Hardest known natural mineral.  Structure: each atom is bonded tetrahedrally to four others, making a 3-dimensional network of puckered six-membered rings of atoms.
• Graphite: One of the softest substances. Structure: each atom is bonded trigonally to three other atoms, making a 2-dimensional network of flat six-membered rings; the flat sheets are loosely bonded.
• Fullerenes: Structure: comparatively large molecules formed completely of carbon bonded trigonally, forming spheroids (of which the best-known and simplest is the buckminsterfullerene or buckyball, because of its soccerball-shaped structure).
• Chaoite: A mineral believed to be formed in meteorite impacts.
• Lonsdaleite: A corruption of diamond.  Structure: similar to diamond, but forming a hexagonal crystal lattice.
• Amorphous Carbon: A glassy substance.  Structure: an assortment of carbon molecules in a non-crystalline, irregular, glassy state.
• Carbon Nanofoam (discovered in 1997): An extremely light magnetic web.  Structure: a low-density web of graphite-like clusters, in which the atoms are bonded trigonally in six- and seven-membered rings.
• Carbon Nanotubes: Tiny tubes. Structure: each atom is bonded trigonally in a curved sheet that forms a hollow cyclinder.
• Aggregated Diamond Nanorods (synthesised in 2005): The most recently discovered allotrope and the hardest substance known to man.
• Lampblack: Consists of small graphitic areas. These areas are randomly distributed, so the whole structure is isotropic.
• "Glassy Carbon": An isotropic substance that contains a high proportion of closed porosity.  Unlike normal graphite, the graphitic layers are not stacked like pages in a book, but have a more random arrangement.

Carbon fibers are similar to Glassy Carbon. Under special treatment (stretching of organic fibers and carbonization) it is possible to arrange the carbon planes in direction of the fiber.  Perpendicular to the fiber axis there is no orientation of the carbon planes. The result are fibers with a higher specific strength than steel.

The system of Carbon allotropes spans a range of extremes:

• Diamond is the hardest mineral known to man (although aggregated diamond nanorods are now believed to be even harder), while graphite is one of the softest.
• Diamond is the ultimate abrasive, while graphite is a very good lubricant.
• Diamond is an excellent electrical insulator, while graphite is a conductor of electricity.
• Diamond is an excellent thermal conductor, while some forms of graphite are used for thermal insulation (i.e. firebreaks and heatshields)
• Diamond is usually transparent, while graphite is opaque.
• Diamond crystallizes in the cubic system while graphite crystallizes in the hexagonal system.
• Amorphous carbon is completely isotropic, while carbon nanotubes are among the most anisotropic materials ever produced.

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, the uncommon Dicarbon Monoxide, C₂O 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, displacing oxygen, which has a lower binding affinity.  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, C₂^2- to form alloys with 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 diamonds.

Carbon has the ability to form long, indefinite chains with interconnecting C-C bonds. This property is called catenation.  Carbon-Carbon bonds are strong, and stable.   This property allows carbon to form an infinite number of compounds; in fact, there are more known carbon-containing compounds than all the compounds of the other chemical elements combined except those of hydrogen (because almost all carbon compounds contain hydrogen).

The simplest form of an organic molecule is the hydrocarbon - a large family of organic molecules that, by definition, are composed of Hydroen atoms bonded to a chain of carbon atoms. Chain length, side chains and functional groups all affect the properties of organic molecules.

Nearly ten million carbon compounds are known, and thousands of these are vital to life processes.  They are also many organic-based reactions of economic importance.

Carbon Cycle

Under terrestrial conditions, conversion of one element 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 petroleum or coal which can burn with the release of carbon dioxide should bacteria not consume it.

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 seconds..

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 years and has been used extensively for radiocarbon dating carbonaceous materials.

The exotic ¹⁹C exhibits a Nuclear halo.

Precautions

Although carbon is relatively safe due to low toxicity and resistance to most chemical attacks (including fire) at normal temperatures, inhalation of fine soot in large quantities can be dangerous.  Diamond dust can do harm as an abrasive if ingested or inhaled.  Carbon may also spawn flames at very high temperatures and burn vigorously and brightly.

The great variety of carbon compounds include such lethal poisons as Cyanide, CN- and Carbon Monoxide, CO; some are essential to life (Glucose).

(L. carbo, charcoal) Carbon, an element of prehistoric discovery, is very widely distributed in nature.  It is found in abundance in the sun, stars, comets, and atmospheres of most plants.  Carbon in the form of microscopic diamonds is found in some meteorites.  Natural diamonds are found in kimberlite of ancient volcanic "pipes," such as 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.  Carbon is found free in nature in three allotropic forms: amorphous, graphite, and diamond.  A fourth form, known as "white" carbon, is now thought to exist. Ceraphite is one of the softest known materials while diamond is one of the hardest. Graphite exists in two forms: alpha and beta.  These have identical physical properties, except for their crystal structure.  Naturally occurring graphites are reported to contain as much as 30% of the rhombohedral (beta) form, whereas synthetic materials contain only the alpha form.  The hexagonal alpha type can be converted to the beta by mechanical treatment, and the beta form reverts to the alpha on heating it above 1000^oC.  In 1969 a new allotropic form of carbon was produced during the sublimation of pyrolytic graphite at low pressures.   Under free-vaporization conditions above ~2550^oK, "white" carbon forms as small transparent crystals on the edges of the planes of graphite.   The interplanar spacings of "white" carbon are identical to those of carbon form noted in the graphite gneiss from the Ries (meteroritic) Crater of Germany.   "White" carbon is a transparent birefringent material.  Little information is presently available about this allotrope.  In combination, carbon is found as carbon dioxide in the atmosphere of the earth and dissolved in all natural waters.  It is a component of great rock masses in the form of carbonates of calcium (limestone), magnesium, and iron.  Coal, petroleum, and natural gas are chiefly hydrocarbons.  Carbon is unique among the elements in the vast number and variety of compounds it can form. With hydrogen, oxygen, nitrogen, and other elements, it forms a very large number of compounds, carbon atom often being linked to carbon atom.  There are close to ten million known carbon compounds, many thousands of which are vital to organic and life processes.  Whitout carbon, the basis for life would be impossible . While it has been thought that silicon might take the place of carbon in forming a host of similar compounds, it is now not possible to form stable compounds with very long chains of silicon atoms.  The atmosphere of Mars contains 96.2% CO₂.  Some of the most important compounds of carbon are carbon dioxide (CO₂), carbon monoxide (CO), carbon disulfide (CS₂), chloroform (CHCl₃), carbon tetrachloride (CCl₄), methane (CH₄), ethylene (C₂H₄), acetylene (C₂H₂), benzene (C₆H₆), acetic acid (CH₃COOH), and their derivatives. Carbon has seven isotopes.  In 1961 the International Union of Pure and Applied Chemistry adopted the isotope carbon-12 as the basis for atomic weights.  Carbon-14, an isotope wiht a half-life of 5715 years, has been widely used to date such materials as wood, archeological specimens, etc. Carbon-13 is now commercially available at a cost of $700/g.

Source: CRC Handbook of Chemistry and Physics, 1913-1995. David R. Lide, Editor in Chief. Author: C.R. Hammond

Carbon, the sixth most abundant element in the universe, has been known since ancient times.  Carbon is most commonly obtained from coal deposits, although it usually must be processed into a form suitable for commercial use.  Three naturally occurring allotropes of Carbon are known to exist: amorphous, graphite and diamond.

Amorphous Carbon is formed when a material containing Carbon is burned without enough Oxygen for it to burn completely. This black soot, also known as lampblack, gas black, channel black or Carbon black, is used to make inks, paints and rubber products.  It can also be pressed into shapes and is used to form the cores of most dry cell batteries, among other things.

Graphite, one of the softest materials known, is a form of Carbon that is primarily used as a lubricant.  Although it does occur naturally, most commercial graphite is produced by treating petroleum coke, a black tar residue remaining after the refinement of crude oil, in an Oxygen-free oven.  Naturally occurring graphite occurs in two forms, alpha and beta. T hese two forms have identical physical properties but different crystal structures.  All artificially produced graphite is of the alpha type.  In addition to its use as a lubricant, graphite, in a form known as coke, is used in large amounts in the production of steel.  Coke is made by heating soft coal in an oven without allowing oxygen to mix with it.  Although commonly called Lead, the black material used in pencils is actually graphite.

Diamond, the third naturally occurring form of Carbon, is one of the hardest substances known.  Although naturally occurring diamond is typically used for jewelry, most commercial quality diamonds are artificially produced.  These small diamonds are made by squeezing graphite under high temperatures and pressures for several days or weeks and are primarily used to make things like diamond tipped saw blades.  Although they posses very different physical properties, graphite and diamond differ only in their crystal structure.

A fourth allotrope of Carbon, known as White Carbon, was produced in 1969.  It is a transparent material that can split a single beam of light into two beams, a property known as birefringence.  Very little is known about this form of Carbon.

Large molecules consisting only of Carbon, known as buckminsterfullerenes, or buckyballs, have recently been discovered and are currently the subject of much scientific interest.  A single buckyball consists of 60 or 70 carbon atoms (C₆₀ or C₇₀) linked together in a structure that looks like a soccer ball.  They can trap other atoms within their framework, appear to be capable of withstanding great pressures and have magnetic and superconductive properties.

Carbon-14, a radioactive isotope of Carbon with a half-life of 5,730 years, is used to find the age of formerly living things through a process known as radiocarbon dating.   The theory behind carbon dating is fairly simple.  Scientists know that a small amount of naturally occurring Carbon is carbon-14.  Although Carbon-14 decays into Nitrogen-14 through beta decay, the amount of carbon-14 in the environment remains constant because new Carbon-14 is always being created in the upper atmosphere by cosmic rays.  Living things tend to ingest materials that contain Carbon, so the percentage of Carbon-14 within living things is the same as the percentage of Carbon-14 in the environment.  Once an organism dies, it no longer ingests much of anything.  The Carbon-14 within that organism is no longer replaced and the percentage of Carbon-14 begins to decrease as it decays.  By measuring the percentage of Carbon-14 in the remains of an organism, and by assuming that the natural abundance of Carbon-14 has remained constant over time, scientists can estimate when that organism died.  For example, if the concentration of Carbon-14 in the remains of an organism is half of the natural concentration of carbon-14, a scientist would estimate that the organism died about 5,730 years ago, the half-life of Carbon-14.

There are nearly ten million known Carbon compounds and an entire branch of chemistry, known as organic chemistry, is devoted to their study.  Many Carbon compounds are essential for life as we know it.  Some of the most common Carbon compounds are: Carbon Dioxide (CO₂), Carbon Monoxide (CO), Carbon Disulfide (CS₂), Chloroform (CHCl₃), Carbon Tetrachloride (CCl₄), Methane (CH₄), Ethylene (C₂H₄), Acetylene (C₂H₂), Benzene (C₆H₆), Ethyl Alcohol (C₂H₅OH) and Acetic Acid (CH₃COOH).