Carbon

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 10 million known compounds. When united with oxygen it forms carbon dioxide which is absolutely 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.

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 methanoic acid, HCO₂H, 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, and the uncommon carbon suboxide, C₃O₂. 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 haemoglobin 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, C₂^2- 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 abnormaly 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

Main article: 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 from somewhere, and 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. 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, and 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.

Precautions

Carbon is relatively safe. Inhalation of fine soot in large quantities can be dangerous. Carbon may catch fire at very high temperatures and burn vigorously (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).

References

On Graphite Transformations at High Temperature and Pressure Induced by Absorption of the LHC Beam, J.M. Zazula, 1997
WebElements.com and EnvironmentalChemistry.com per the guidelines at Wikipedia's WikiProject Elements

Carbon

Organic compounds

Carbon chains

Carbon cycle

Isotopes

Precautions

References

See also

Elements in humans

Carbon

External links