Carbon

Carbon: the essentials

 Brief description: carbon is a Group 14 element and is distributed very widely in nature. It is found in abundance in the sun, stars, comets, and atmospheres of most planets.

Carbon is found free in nature in three allotropic forms: amorphous, graphite, and diamond (further details). Graphite is one of the softest known materials while diamond is one of the hardest. Carbon, as microscopic diamonds, is found in some meteorites. Natural diamonds are found in ancient volcanic "pipes" such as found in South Africa. Diamonds are also recovered from the ocean floor off the Cape of Good Hope.

Table: basic information about and classifications of carbon.

Name: Carbon Symbol: C Atomic number: 6 Atomic weight: 12.0107 (8) [see notes g r] Standard state: solid at 298 K CAS Registry ID: 7440-44-0

Group in periodic table: 14 Group name: (none) Period in periodic table: 2 Block in periodic table: p-block Colour: graphite is black, diamond is colourless Classification: Non-metallic

A diamond ring.

More recently, another form of carbon, buckminsterfullerene, C₆₀, has been discovered. This new form of carbon is the subject of great interest in research laboratories today.

Carbon is present as carbon dioxide in the atmosphere and dissolved in all natural waters. It is a component of rocks as carbonates of calcium (limestone), magnesium, and iron. The atmosphere of Mars contains 96 % CO₂.

Coal, petroleum, and natural gas are chiefly hydrocarbons. Carbon is unique among the elements in the vast number of variety of compounds it can form. Organic chemistry, a 1/112th subset of inorganic chemistry, is the study of carbon and its compounds. While silicon might take the place of carbon in forming a host of related compounds, it is not possible currently to form stable compounds with very long chains of silicon atoms.

In 1961 the International Union of Pure and Applied Chemistry (IUPAC) adopted the isotope ¹²C as the basis for atomic weights. Carbon-14, ¹⁴C, an isotope with a half-life of 5730 years, is used to date such materials as wood, archeological specimens, etc. Carbon-13, ¹³C, is particularly useful for isotopic labelling studies since it is not radioactive, but is a spin I = ¹/₂ nucleus and therefore a good NMR nucleus.

Cartoon by Nick D Kim (nearingzero.net, used by permission).

This sample is from The Elements Collection, an attractive and safely packaged collection of the 92 naturally occurring elements that is available for sale.

Isolation

Isolation: carbon is available in nature as graphite and (to a much lesser extent!) as diamond. Artificial graphite is made by the reaction of coke with silica (SiO₂).

SiO₂ + 3C (2500°C) → "SiC" → Si (g) + C(graphite)

Artificial diamonds are made by the application of heat and pressure (> 125 kBar) in the presence of a catalyst such as iron, chromium or platinum. It seems that the metal melts on the carbon surface, the graphite dissolves in the metal film, and the less soluble diamond precipitates out. The introduction of nitrogen as an impurity gives yellowish diamonds while boron impurities give bluish colours.

A new form of carbon, buckminsterfullerene with formula C₆₀ is formed in the treatment of graphite by lasers and is now commercially available in small quantities.

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Carbon	Carbone
Kohlenstoff	Koolstof
Carbonio	Carbono
Kol	Carbono