Carbon is one of the most important chemical elements. Industry uses it in a wide variety of products, and all living things are based on carbon. Without carbon, life would be impossible! Yet carbon makes up less than 0.03 percent of the earth’s crust. Pure carbon exists in nature in the form of diamonds, and in graphite. Both forms are pure carbon with different crystal structures. Another form of pure carbon, called amorphous carbon, consists of graphite-like particles too tiny to see without a microscope.
Diamonds and graphite have important industrial uses. But much of the carbon used in industry is amorphous carbon. Amorphous carbon and ash result when materials containing carbon are burned or heated without enough oxygen for them to burn completely. For example, if oil, natural gas, or other petroleum fuels are burned in limited supplies of air, powdery-black soot of amorphous carbon, called carbon black, is formed. Carbon black is used in rubber products and paint. Charcoal is used as a cooking fuel and ivory black, made by heating ivory, is used as a pigment in paint.
Most carbon occurs in combination with other elements. For example, the carbon dioxide in the air is a compound of carbon and oxygen. Other compounds containing carbon include minerals such as limestone, and fuels such as coal and petroleum. Carbon compounds make up the living tissues of all animals and plants. There are over one million known carbon compounds (still growing rapidly every year), which is over the sum total of all the other elements combined. The largest group of these compounds are the ones composed of carbon and hydrogen. Carbon also forms another series of compounds, which is classified as inorganic, but is a much smaller number than the organic compounds. These millions of compounds combine in various ways to produce an almost unlimited number of carbon-containing substances. Organic chemistry, which is the name given to the study of compounds made by and derived from living organisms, is primarily a study of carbon compounds.
Carbon and its compounds are found widely dispersed in nature. It is estimated that carbon makes up 0.032% of the Earth’s crust. Free carbon is found in large deposits as coal, an amorphous form of the element that contains additional complex carbon-hydrogen-nitrogen compounds. Pure crystalline carbon is found as graphite and in small amounts as diamonds.
Extensive amounts of carbon are found in the form of its compounds. In the atmosphere, carbon is present in amounts up to 0.03% by volume as carbon dioxide. Various minerals such as limestone, dolomite, marble, and chalk all contain carbon in the form of carbonate. All plant and animal life is composed of complex organic compounds containing carbon combined with hydrogen, oxygen, nitrogen, and other elements. The remains of past plant and animal life are found as deposits of petroleum, asphalt, and bitumen. Deposits of natural gas contain compounds that are composed of carbon and hydrogen.
The forms of pure carbon vary widely depending upon which crystal structure the atoms take. In diamond, the carbon atoms are arranged in a close framework that makes diamond one of the hardest substances known. Diamonds are used to cut other hard materials. However, graphite is so soft that it is widely used to lubricate moving machine parts. Its carbon atoms are arranged in flat sheets or layers that can easily slide back and forth over each other.
Carbon has many other uses, ranging from ornamental applications of the diamond in jewelry to the black-colored pigment of carbon black in automobile tires and printing inks. Another form of carbon, graphite, is used for high-temperature crucibles, arc light and dry-cell electrodes, lead pencils, and as a lubricant. It is also used in fishing rods, golf clubs, and tent poles. Charcoal is used as an absorbent for gases and as a decoloring agent.
The compounds of carbon also have many uses. Carbon dioxide is used for the carbonation of beverages, for fire extinguishers, and in the solid state as a refrigerant. Another oxide of carbon, carbon monoxide, finds use as a reducing agent for many metallurgical processes. Carbon tetrachloride and carbon disulfide are important solvents for industrial uses. Gaseous dichlorodifluoromethane, commonly known as Freon, is used in refrigeration devices. Calcium carbide is used to prepare acetylene, which is used for the welding and