6
  C  
12.010700
Carbon

Name: Carbon
Symbol: C
Atomic Number: 6
Atomic Weight: 12.010700
Family:  Non Metals
CAS RN: 7440-44-0
Description: As graphite is black as diamond is colorless.
State (25C): Solid
Oxidation states: +2, +4, -4

Molar Volume: 5.34 cm3/mole
Valence Electrons: 2p2

Boiling Point:  5100K, 4827C, 8721F
Melting Point:
3773K, 3500C, 6332F
Electrons Energy Level: 2, 4
Isotopes: 12 + 2 Stable
Heat of Vaporization: 355.8 kJ/mol
Heat of Fusion: unknown
Density: 2.26 g/cm3 @ 300K
Specific Heat: 0.71 J/gK
Atomic Radius: 0.91
Ionic Radius: unknown
Electronegativity: 2.55 (Pauling); 2.5 (Allrod Rochow)
Vapor Pressure: 0 mmHg @ 20C
Carbon is the sixth most abundant element in the known universe but not nearly as common on the earth, despite the fact that living organisms contain significant amounts of the element.   Common carbon compounds in the environment include the gases carbon dioxide (CO2) and methane (CH4).

Carbon exists in several forms called allotropes.   Diamond is one form with a very strong crystal lattice, known as a precious gem from the most ancient records.  Graphite is another allotrope in which the carbon atoms are arranged in planes which are loosely attracted to one another (hence its use as a lubricant).  The recently discovered fullerenes are yet another form of carbon.

Most elemental carbon is taken from the ground in the form of coal but certainly diamonds should not be ignored! Carbon has a very high melting and boiling point and rapidly combines with oxygen at elevated temperatures. In small amounts it is an excellent hardener for iron, yielding the various steel alloys upon which so much of modern construction depends.

An important (but rare) radioactive isotope of carbon, C-14, is used to date ancient objects of organic origin. It has a half-life of 5730 years but there is only 1 atom of C-14 for every 1012 atoms of C-12 (the usual isotope of carbon).

6
C
12.02
14
Si
28.08
32
Ge
72.15
50
Sn
118.7
82
Pb
207.2
114
Uuq
285.0

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.

1s2
2s2 2p2

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:

Biosphere, oceans, atmosphere.......3.7 x 1018 moles

Crust
Organic Carbon ...............................1100 x 1018 moles
Carbonates.......................................5200 x 1018 moles

Earths Mantle...........................100000 x 1018 moles

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

Allotropes

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.  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.

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

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.

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  charcoal, lampblack (soot), gas black, channel black, Carbon black and activated Carbon, 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.

300px-Carbon_basic_phase_diagram.jpg (17433 bytes)

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.

Graphite forms at normal pressures whereby 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 1000C.  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.  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.  Although commonly called Lead, the black material used in pencils is actually graphite.

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.

Diamond, the third naturally occurring form of Carbon, is one of the hardest substances known.  Formed at very high pressures each atom is bonded to four others.  Diamond has the same cubic structure as Silicon and Germanium and, because of the strength of the Carbon-Carbon bonds, is together with the isoelectronic Boron Nitride (BN) the hardest substance in terms of resistance to scratching.  Under some conditions, carbon crystallizes as Lonsdaleite, a form similar to diamond but hexagonal.  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.

White Carbon, a fourth (lesser known) allotrope of 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.

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".

These large molecules also known as buckminsterfullerenes (Buckyballs) 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 non-carbon atoms within their framework and appear to be capable of withstanding great pressures.  They also have magnetic and superconductive properties.

A nanofoam allotrope has been discovered which is ferromagnetic.

333px-Eight_Allotropes_of_Carbon.jpg (48757 bytes)

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

Carbon allotropes include:

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:

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, C22- 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 Dioxide, CO2 Carbon Monoxide, CO
Carbon Disulfide, CS2 Chloroform, CHCl3
Carbon Tetrachloride, CCl4 Methane, CH4
Ethylene, C2H4 Acetylene, C2H2
Benzene, C6H6 Ethyl Alcohol, C2H5OH
Acetic Acid, CH3COOH Carbon Suboxide, C3O2
Dicarbon Monoxide, C2O Carbon Trioxide, CO3
Carborundum, SiC Carbonic Acid, H2CO3

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.

Carbon-14, the radioactive isotope of Carbon with a half-life of 5,730 years, is central in finding the age of formerly living things through a process known as radiocarbon dating.   This theory is based on the following:  Scientists know that a small amount of naturally occurring Carbon is carbon-14.  While Carbon-14 decays into Nitrogen-14 through beta decay, the amount of carbon-14 in the environment remains constant due to new Carbon-14 being created in the upper atmosphere by cosmic rays.  Living things ingest materials that contain Carbon, thus 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 Carbon containing material.  The Carbon-14 within the organism is no longer replaced and the percentage of Carbon-14 begins to decline 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.

atom.gif (700 bytes)

Isotope Atomic Mass Half-Life
C8 8.0377 230 keV
C9 9.031 126.5 ms
C10 10.0169 19.255 seconds
C11 11.0114 20.39 minutes
C12 12. Stable
C13 13.0034 Stable
C14 14.0032 5730 years
C15 15.0106 2.449 seconds
C16 16.0147 0.747 seconds
C17 17.0226 193 ms
C18 18.0268 95 ms
C19 19.035 46 ms
C20 20.04 14 ms
C21 21.049  
C22 22.056 >200 ns

Precautions

80px-Flammable.jpg (2186 bytes) 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.

40px-Skull_and_crossbones.svg.jpg (1420 bytes) The great variety of carbon compounds include such lethal poisons as Cyanide, CN- and Carbon Monoxide, CO; some are essential to life (Glucose).

atom.gif (700 bytes)

Carbon Data

Atomic Radius (): 0.91
Atomic Volume cm3/mol : 4.58cm3/mol
Covalent Radius: 0.77
Crystal Structure: Hexagonal
Ionic Radius: unknown

Chemical Properties

Electrochemical Equivalents: unknown
Electron Work Function: unknown
Electronegativity: 2.55 (Pauling); 2.5 (Allrod Rochow)
Heat of Fusion: unknown
Incompatibilities: Very Strong Oxidizers such as Fluorine, Chlorine Trifluoride & Potassium Peroxide
First Ionization Potential: 11.26
Second Ionization Potential: 24.383
Third Ionization Potential: 47.887
Valence Electron Potential: unknown
Ionization Energy (eV): 11.260 eV

Physical Properties

Atomic Mass Average: 12.011
Boiling Point: 5100K, 4827C, 8721F
Melting Point: 3773K, 3500C, 6332F
Heat of Vaporization: 355.8 kJ/mol
Coefficient of Lineal Thermal Expansion/K-1: 1.19E-6
Electrical Conductivity: 0.00061 106/cm
Thermal Conductivity: 1.29 W/cmK
Density: 2.26 g/cm3 @ 300K
Enthalpy of Atomization: unknown
Enthalpy of Fusion: 104.6 kJ/mole
Enthalpy of Vaporization: 716.7 kJ/mole
Flammability Class: Combustible solid (graphite)
Molar Volume: 5.34 cm3/mole
Optical Refractive Index: 2.417 (diamond)
Relative Gas Density (Air=1): unknown
Specific Heat: 0.71 J/gK
Vapor Pressure: 0 mmHg @ 20C
Estimated Crustal Abundance: 2.00102 milligrams per kilogram
Estimated Oceanic Abundance: 2.8101 milligrams per liter


(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 1000oC.  In 1969 a new allotropic form of carbon was produced during the sublimation of pyrolytic graphite at low pressures.   Under free-vaporization conditions above ~2550oK, "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