Carbon: the essentials
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.
Carbon: historical information
Carbon as charcoal, soot and coal has been used since prehistoric times. Carbon as diamond has also been known since very ancient times. The recognition that soot (amorphous carbon), graphite (another form of carbon) and diamond are all forms of carbon.
A fourth form, buckminsterfullerene, formula C60, whose framework is reminiscent of the seams in an Association Football ("soccer") ball, is the subject of considerable interest at present and was only discovered a few years ago in work involving Harry Kroto, a Sheffield graduate.
Sometime prior to the autumn of 1803, the Englishman John Dalton was able to explain the results of some of his studies by assuming that matter is composed of atoms and that all samples of any given compound consist of the same combination of these atoms. Dalton also noted that in series of compounds, the ratios of the masses of the second element that combine with a given weight of the first element can be reduced to small whole numbers (the law of multiple proportions). This was further evidence for atoms. Dalton's theory of atoms was published by Thomas Thomson in the 3rd edition of his System of Chemistry in 1807 and in a paper about strontium oxalates published in the Philosophical Transactions. Dalton published these ideas himself in the following year in the New System of Chemical Philosophy. The symbol used by Dalton for carbon is shown below. [See History of Chemistry, Sir Edward Thorpe, volume 1, Watts & Co, London, 1914.]
Carbon: physical properties
Carbon: orbital properties
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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