has been one of the most useful metals for more than 5,000 years. In ancient times, the chief source of copper for the peoples near the Mediterranean Sea was the island of Cyprus. As a result, the metal became known as Cyprian metal. Both the word copper and the chemical symbol for the element, Cu, come from cuprum, the Roman name for Cyprian metal.

Chemical Properties

Copper is one of the Third Transition Metals. It has an atomic number of 29, and an atomic weight of 63.54. It melts at 1,083.4° C and boils at 2,567° C. Copper has a density of about 560 pounds per cubic foot (8,970 kilograms per cubic meter) and a specific gravity of 8.92. Cold-rolled copper has a tensile strength from 50,000 to 70,000 pounds per square inch (3,500 to 4,900 kilograms per square centimeter). Copper keeps its strength and toughness up to a temperature of about 400° F. (204° C).

Physical Properties

Copper is probably best known for its ability to conduct electricity. Silver is the only better conductor, but silver is too expensive for common use. Copper is also an excellent conductor of heat, making it useful in cooking utensils, radiators, and refrigerators.

Pure copper is highly malleable. It does not crack when hammered, stamped, forged, die-pressed, or spun into unusual shapes. It can be worked either hot or cold, and can be rolled into sheets less than 1/500 inch (0.05 millimeter) thick. Cold rolling changes the physical properties of copper and increases its strength.

Copper posses great ductility, the ability to be drawn into thin wires without breaking. A copper bar 4 inches (10 centimeters) square can be heated, rolled, and drawn into a round wire thinner than a human hair. Such a wire would be more than 20 million times longer than the bar used to make it.

Copper is very resistant to corrosion. In damp air, it turns from a reddish-orange to a reddish-brown color. After long exposure, copper becomes coated with a green film called patina, which protects it against further corrosion.

Sources

Most copper comes from about seven kinds of ores, most of which usually contain less than 4 per cent copper. The chief copper ores are sulfides, which include bornite, chalcocite (copper glance), and chalcopyrite (copper pyrite). Oxidized ores, such as azurite, cuprite, and malachite, also yield valuable amounts of copper. Almost pure copper, called native copper, rarely occurs in nature.

Every continent on Earth has copper deposits, but much of the world's copper comes from the mountain ranges extending from Alaska to the tip of South America. In some places, miners dig copper ore from mines far below the earth's surface. Elsewhere, they remove it from open-pit mines. Most copper in the United States comes from open pits.

Uses

Pure copper is used to make electrical wire, plumbing pipe, cooking utensils, roofing sheets, photoengraving plates, and many other products.

Combined with other metals, copper forms such alloys as brass (copper alloyed with zinc) and bronze (copper alloyed with tin), which in turn can be made into a wide variety of products. Perhaps the most familiar copper alloy product is the U.S. penny, which is made with bronze.

Chemical compounds of copper help improve soil and destroy harmful insects. Copper compounds in paint help protect materials against corrosion.

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