CARBON

                             

                                              
CARBON

Carbon is the 15th most abundant element in the Earth's crust, and the fourth most abundant element in the universe by mass after hydrogen, helium, and oxygen. It is present in all known life forms, and in the human body carbon is the second most abundant element by mass (about 18.5%) after oxygen. This abundance, along with the unique diversity of organic compounds and their unusual catenation ability at the temperatures commonly encountered on Earth, make this element the chemical basis of all known life.

HISTORICAL BACKGROUND

Carbon was first discovered as charcoal in prehistoric times. The name of the discoverer will probably never be known. The element's name in many languages is derived from the words for charcoal or for coal; the English "carbon" is derived from the Latin name for burnt wood (carbo). Carbon wasn't recognized as an element until the seventeenth century, after Robert Boyle suggested that an element was a substance that could not be decomposed into simpler substances. Antoine Lavoisier's pioneering chemistry textbook Traité Élémentaire de Chimie, published in Paris in 1789, lists carbon as an "oxidizable and acidifiable nonmetallic element 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. Three naturally occurring allotropes (i.e the existence of a substance in different forms in the same physical state) of carbon are known to exist as diamond,  graphite, and buckminsterfullerene.

SIGNIFICANCE

All living organisms contain carbon; the human body is about 18% carbon by weight. In green plants   carbon dioxide and water are combined to form simple sugars (carbohydrates);  light from the sun provides the energy for this process (photosynthesis ).  The energy from the sun is stored in the chemical bonds of the sugar molecule. Anabolism, the synthesis of complex compounds (such as fats , proteins , and nucleic acids ) from simpler substances, involves the utilization of energy stored by photosynthesis. Catabolism is the release of stored energy by the oxidative destruction of organic compounds; water and carbon dioxide are two byproducts of catabolism. This continuing synthesis and degradation involving carbon dioxide is known as the biological carbon cycle .Carbon compounds have plenty of uses. Carbon dioxide is used in drinks carbonatation, in fire extinguishers and, in solid state, as a cooler (dry ice). Carbon monoxide is used as reduction agent in many metallurgic processes. Carbon tetrachloride and carbon disulphide are important industrial solvents. Freon is used in cooling systems. Calcium carbide is used to prepare acetylene; it’s used for welding and cutting metals, as well as for preparation of other organic compounds. Other metallic carbides have important uses as heat-resistants and metal cutters.

ADVERSE EFFECTS

Elemental carbon is of very low toxicity. Chronic inhalation exposure to carbon black may result in temporary or permanent damage to lungs and heart. Pneumoconiosis has been found in workers engaged in the production of carbon black. Skin conditions such as inflammation of the hair follicles, and oral mucosal lesions have also been reported from skin exposure. Carcinogenicity- Carbon black has been listed by the International Agency for Research on Cancer (IARC) within Group 3 (The agent is not classifiable as to its

carcinogenicity to humans). Some simple carbon compound can be very toxic, such as

carbon monoxide (CO) or cyanide (CN-). Carbon 14 is one of the radionuclides involved in

atmospheric testing of nuclear weapons, which began in 1945, with a US test, and ended in 1980 with a Chinese test. It is among the long-lived radionuclides that have produced and will continue to produce increased cancers risk for decades and centuries to come. It also can cross

the placenta, become organically bound in developing cells and hence endanger fetuses.

Most  we eat is made up of compounds of carbon, giving a total carbon intake og 300 g/day. Digestion consist of breaking these compounds down into molecules than can be adsorbed to the wall of the stomach or intestine. There they are transported by the blood to sites where

they are utilized or oxidised to release the energy they contain.