The metal carbides. Theyhave properties ranging from

The metal carbides. Theyhave properties ranging from

The History of CarbonI. IntroductionA. The History of CarbonII. Occurrences in NatureA. DiamondB. GraphiteC. Coal and CharcoalD.

Amorphous CarbonIII. Carbon CompoundsA. InorganicB. OrganicIV.

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The Carbon CycleIV. ConclusionCarbon, an element discovered before history itself, is one of the mostabundant elements in the universe. It can be found in the sun, the stars,comets, and the atmospheres of most planets. There are close to ten millionknown carbon compounds, many thousands of which are vital to the basis of lifeitself (WWW 1).

Carbon occurs in many forms in nature. One of its purest forms is diamond.Diamond is the hardest substance known on earth. Although diamonds found innature are colorless and transparent, when combined with other elements itscolor can range from pastels to black. Diamond is a poor conductor of heat andelectricity. Until 1955 the only sources of diamond were found in deposits ofvolcanic origin.

Since then scientists have found ways to make diamond fromgraphite and other synthetic materials. Diamonds of true gem quality are notmade in this way (Beggott 3-4).Graphite is another form of carbon. It occurs as a mineral in nature, but itcan be made artificially from amorphous carbon. One of the main uses forgraphite is for its lubricating qualities. Another is for the lead in pencils.Graphite is used as a heat resistant material and an electricity conductor.

Itis also used in nuclear reactors as a lubricator (Kino*censored*a 119-127).Amorphous carbon is a deep black powder that occurs in nature as a component ofcoal. It may be obtained artificially from almost any organic substance byheating the substance to very high temperatures without air.

Using this method,coke is produced from coal, and charcoal is produced from wood. Amorphouscarbon is the most reactive form of carbon. Because amorphous carbon burnseasily in air, it is used as a combustion fuel.

The most important uses foramorphous carbon are as a filler for rubber and as a black pigment in paint (WWW2).There are two kinds of carbon compounds. The first is inorganic. Inorganiccompounds are binary compounds of carbon with metals or metal carbides. Theyhave properties ranging from reactive and saltlike; found in metals such assodium, magnesium, and aluminum, to an unreactive and metallic, such as titaniumand niobium (Beggott 4).

Carbon compounds containing nonmetals are usually gases or liquids with lowboiling points. Carbon monoxide, a gas, is odorless, colorless, and tasteless.It forms during the incomplete combustion of carbon (Kino*censored*a 215-223).

It ishighly toxic to animals because it inhibits the transport of oxygen in the bloodby hemoglobin (WWW 2). Carbon dioxide is a colorless, almost odorless gas thatis formed by the combustion of carbon. It is a product that results fromrespiration in most living organisms and is used by plants as a source of carbon.Frozen carbon dioxide, known as dry ice, is used as a refrigerant.Fluorocarbons, such as Freon, are used as refrigerants (Kino*censored*a 225-226).

Organic compounds are those compounds that occur in nature. The simplestorganic compounds consist of only carbon and hydrogen, the hydrocarbons. Thestate of matter for organic compounds depends on how many carbons are containedin it. If a compound has up to four carbons it is a gas, if it has up to 20carbons it is a liquid, and if it has more than 20 carbons it is a solid(Kino*censored*a 230-237).

The carbon cycle is the system of biological and chemical processes that makecarbon available to living things for use in tissue building and energy release(Kino*censored*a 242). All living cells are composed of proteins consisting of carbon,hydrogen, oxygen, and nitrogen in various combinations, and each living organismputs these elements together according to its own genetic code. To do this theorganism must have these available in special compounds built around carbon.These special compounds are produced only by plants, by the process ofphotosynthesis.

Photosynthesis is a process in which chlorophyll traps and usesenergy from the sun in the form of light. Six molecules of carbon dioxidecombine with six molecules of water to form one molecule of glucose (sugar).The glucose molecule consists of six atoms of carbon, twelve of hydrogen, andsix of oxygen. Six oxygen molecules, consisting of two oxygen atoms each, arealso produced and are discharged into the atmosphere unless the plant needsenergy to live. In that case, the oxygen combines with the glucose immediately,releasing six molecules of carbon dioxide and six of water for each molecule ofglucose (Beggott 25-32). The carbon cycle is then completed as the plantobtains the energy that was stored by the glucose.

The length of time requiredto complete the cycle varies. In plants without an immediate need for energy,the chemical processes continue in a variety of ways. By reducing the hydrogenand oxygen content of most of the sugar molecules by one water molecule andcombining them to form large molecules, plants produce substances such as starch,inulin , and fats and store them for future use. Regardless of whether thestored food is used later by the plant or consumed by some other organism, themolecules will ultimately be digested and oxidized, and carbon dioxide and waterwill be 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, eventuallythese too are oxidized and form carbon dioxide and water as cells wear out andare broken down, or as the organisms die.

In either case, a new set oforganisms, ranging from fungi to the large scavengers, use the waste products ortissues for food, digesting and oxidizing the substances for energy release (WWW1).At various times in the Earth’s history, some plant and animal tissues havebeen protected by erosion and sedimentation from the natural agents ofdecomposition and converted into substances such as peat, lignite, petroleum,and coal. The carbon cycle, temporarily interrupted in this manner, iscompleted as fuels are burned, and carbon dioxide and water are again added tothe atmosphere for reuse by living things, and the solar energy stored byphotosynthesis ages ago is released (Kino*censored*a 273-275).Almost everything around us today has some connection with carbon or a carboncompound. Carbon is in every living organism. Without carbon life would notexist as we know it.Science Essays

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