is one of the most important chemical elements, yet it makes up less than 0.03 per cent of the Earth's crust. It has been known since prehistoric times. The name carbon comes from carbo, or charcoal.

Chemical Properties

Carbon is a member of the Boron and Carbon Families of elements. It has an atomic number of 6 and an atomic weight of 12.01115. It does not melt, but it sublimes at about 3,500° C. That is, it changes from a solid directly to a gas. At room temperature, pure carbon does not react chemically, but its compounds unite easily with other elements and compounds. Pure carbon will not dissolve in any common solvent.

Forms of Carbon

Pure carbon exists in nature in the form of diamonds, and in graphite, such as that used in some lead pencils. Both forms are pure carbon with different crystal structures. Another form of pure carbon, called amorphous carbon, consists of graphitelike particles too tiny to see without a microscope.

Occurence

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 (calcium carbonate), and fuels such as coal and petroleum. Carbon compounds make up the living tissues of all animals and plants. There are about one million known carbon compounds, which combine in various ways to produce an almost unlimited number of carbon-containing substances.

Uses

Diamonds are highly prized in and of themselves as precious gems. In diamond, the carbon atoms are arranged in a close framework that makes diamond one of the hardest substances known to man. Diamonds are used to cut other hard materials. In contrast, graphite is so soft that it can be 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.

If oil, natural gas, or other petroleum fuels are burned in limited supplies of air, a powdery-black soot of amorphous carbon, called carbon black (also called lampblack) is formed. Carbon black is used in printing inks, paint, and rubber products.

Animal charcoal, also called boneblack, results from heating bones without exposing them to air. Wood charcoal results from heating wood without enough air to burn it completely. The various kinds of charcoal are used to remove the brown color from sugar and to filter impurities and odors from the air. Charcoal is also used as a cooking fuel.

Coke, an important fuel used in making steel, results from heating soft coal without oxygen, as in making charcoal. Ivory black, made by heating ivory, is sometimes used as a pigment in paint.

Carbon in its almost endless variety of compounds is an indispensable source of such varied everyday products as nylon and gasoline, perfume and plastics, shoe polish, and TNT.