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CARBON

(L. carbo, charcoal)

C  at. wt. 12 exactly (C12)
   at. wt. (natural carbon) 12.011100
   at. no. 6
   graphite sublimes at 3367 ±25°C
   m.p.   3550°C
   b.p.   4827°C 
   sp. gr. amorphous 1.8-2.1
   sp. gr. graphite 1.9-2.3
   sp. gr. diamond 3.15-3.53 (Gem 3.513) (25°C)
   valence 2, 3, or 4.
Electronic configuration
 SHELL  K L M N O P Q
 SUB  SHELL He Neon Argon Krypton Xenon Radon Eka-radon
1s 2s 2p 3s 3p 3d 4s 4p 4d 5s 5p 4f 5d 6s 6p 5f 6d 7s 7p
Carbon 1s22s22p2          
Symbol 3P0
Carbon, an element of prehistoric discoyery, is very widely distributed in nature, It is found in abundance in the sun, stars, comets, and atmospheres of most planets. Carbon in the form of microscopic diamonds is found in some meteor- ites. 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 fouith form, known as "white" carbon, is now thought to exist. Graphite is one of the softest known materials while diamond is one of the hardest. Graphite exists in two forms: alpha 4nd 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 10000C. In 1969 a new allotropic form of carbon was produced during the sublimation of pyrolytic graphite at low pressures. Under free-vaporization condi- tions above 25500K, "white" carbon forms as small trans- parent crystals on the edges of the basal planes of graphite. The interplanar spacings of "white" carbon are identical to those of a carbon form noted in the graphitic gneiss from the Ries (meteoritic) 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 com pounds it can form. With hydrogen, oxygen, and nitrogen, and other elements, it forms an infinite number of com- pounds, carbon atom often being linked to carbon atom. There are upwards of a million or more known carbon compounds, many thousands of which are vital to organic and life processes. Without 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 com- pounds, it is now not p6ssible to form stable compounds with very long chains of silicon atoms. Some of the most important compounds of carbon are: carbon dioxide (C02), carbon monoxide (CO), carbon disulfide (C52), chloroform (CHCl3), carbon tetrachloride (CCI4), methane (CH4), ethylene (C2H4), acetylene (C2H2), benzene (C6H6), ethyl alcohol (C2H5OH), acetic acid (CH3COOH), and their derivatives. Carbon has seven isotopes. In 1961 the Inter- national Union of Pure and Applied Chemistry adopted the isotope carbon- 12 as the basis for atomic weights. Carbon- 14, an isotope with a half-life of 5730 yrs, has been widely used to date such materials as wood, archeological speci- mens, etc. Carbon-13 is now commercially available at a cost of $700/gm.

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