I.Introduction A.The History of CarbonII.Occurrences in Nature A.Diamond B.Graphite C.Coal and Charcoal D.Amorphous CarbonIII.Carbon Compounds A.Inorganic B.OrganicIV.The Carbon CycleIV.ConclusionCarbon, an element discovered before history itself, is one of themost abundant elements in the universe. It can be found in the sun, thestars, comets, and the atmospheres of most planets. There are close to tenmillion known carbon compounds, many thousands of which are vital to thebasis of life itself (WWW 1). Carbon occurs in many forms in nature. One of its purest forms isdiamond. Diamond is the hardest substance known on earth. Althoughdiamonds found in nature are colorless and transparent, when combined withother elements its color can range from pastels to black. Diamond is apoor conductor of heat and electricity. Until 1955 the only sources ofdiamond were found in deposits of volcanic origin. Since then scientistshave found ways to make diamond from graphite and other syntheticmaterials. Diamonds of true gem quality are not made in this way (Beggott3-4). Graphite is another form of carbon. It occurs as a mineral innature, but it can be made artificially from amorphous carbon. One of themain uses for graphite is for its lubricating qualities. Another is forthe “lead” in pencils. Graphite is used as a heat resistant material andan electricity conductor. It is also used in nuclear reactors as alubricator (Kinoshita 119-127). Amorphous carbon is a deep black powder that occurs in nature as acomponent of coal. It may be obtained artificially from almost any organicsubstance by heating the substance to very high temperatures without air. Using this method, coke is produced from coal, and charcoal is producedfrom wood. Amorphous carbon is the most reactive form of carbon. Becauseamorphous carbon burns easily in air, it is used as a combustion fuel. Themost important uses for amorphous carbon are as a filler for rubber and asa black pigment in paint (WWW 2). There are two kinds of carbon compounds. The first is inorganic. Inorganic compounds are binary compounds of carbon with metals or metalcarbides. They have properties ranging from reactive and saltlike; foundin metals such as sodium, magnesium, and aluminum, to an unreactive andmetallic, such as titanium and niobium (Beggott 4). Carbon compounds containing nonmetals are usually gases or liquidswith low boiling points. Carbon monoxide, a gas, is odorless, colorless,and tasteless. It forms during the incomplete combustion of carbon(Kinoshita 215-223). It is highly toxic to animals because it inhibits thetransport of oxygen in the blood by hemoglobin (WWW 2). Carbon dioxide isa colorless, almost odorless gas that is formed by the combustion ofcarbon. It is a product that results from respiration in most livingorganisms and is used by plants as a source of carbon. Frozen carbondioxide, known as dry ice, is used as a refrigerant. Fluorocarbons, suchas Freon, are used as refrigerants (Kinoshita 225-226). Organic compounds are those compounds that occur in nature. Thesimplest organic compounds consist of only carbon and hydrogen, thehydrocarbons. The state of matter for organic compounds depends on howmany carbons are contained in it. If a compound has up to four carbons it
is a gas, if it has up to 20 carbons it is a liquid, and if it has morethan 20 carbons it is a solid (Kinoshita 230-237). The carbon cycle is the system of biological and chemical processesthat make carbon available to living things for use in tissue building andenergy release (Kinoshita 242). All living cells are composed of proteinsconsisting of carbon, hydrogen, oxygen, and nitrogen in variouscombinations, and each living organism puts these elements togetheraccording to its own genetic code. To do this the organism must have theseavailable in special compounds built around carbon. These specialcompounds are produced only by plants, by the process of photosynthesis. Photosynthesis is a process in which chlorophyll traps and uses energy fromthe sun in the form of light. Six molecules of carbon dioxide combine withsix molecules of water to form one molecule of glucose (sugar). Theglucose molecule consists of six atoms of carbon, twelve of hydrogen, andsix of oxygen. Six oxygen molecules, consisting of two oxygen atoms each,are also produced and are discharged into the atmosphere unless the plantneeds energy to live. In that case, the oxygen combines with the glucoseimmediately, releasing six molecules of carbon dioxide and six of water foreach molecule of glucose (Beggott 25-32). The carbon cycle is thencompleted as the plant obtains the energy that was stored by the glucose. The length of time required to complete the cycle varies. In plantswithout an immediate need for energy, the chemical processes continue in avariety of ways. By reducing the hydrogen and oxygen content of most ofthe sugar molecules by one water molecule and combining them to form largemolecules, plants produce substances such as starch, inulin , and fatsand store them for future use. Regardless of whether the stored food isused later by the plant or consumed by some other organism, the moleculeswill ultimately be digested and oxidized, and carbon dioxide and water willbe discharged. Other molecules of sugar undergo a series of chemicalchanges and are finally combined with nitrogen compounds to form proteinsubstances, which are then used to build tissues (WWW 2). Although protein substances may pass from organism to organism,eventually these too are oxidized and form carbon dioxide and water ascells wear out and are broken down, or as the organisms die. In eithercase, a new set of organisms, ranging from fungi to the large scavengers,use the waste products or tissues for food, digesting and oxidizing thesubstances for energy release (WWW 1). At various times in the Earth’s history, some plant and animaltissues have been protected by erosion and sedimentation from the naturalagents of decomposition and converted into substances such as peat,lignite, petroleum, and coal. The carbon cycle, temporarily interrupted inthis manner, is completed as fuels are burned, and carbon dioxide and waterare again added to the atmosphere for reuse by living things, and the solarenergy stored by photosynthesis ages ago is released (Kinoshita 273-275). Almost everything around us today has some connection with carbonor a carbon compound. Carbon is in every living organism. Without carbonlife would not exist as we know it.
1.Beggott, Jim Great Balls of Carbon New Scientist, July 6, 19912.Kinoshita, Kim Carbon Compounds Random, New York 119-27519873.WWW Carbon http://www.usc.edu/chem/carbon.html 19954.WWW Carbon Compounds http://www.harvard.edu/depts/chem/carbon.html1995