Matter & Energy

Matter is composed of atoms or groups of atoms called molecules. The arrangement of particles in a material depends on the physical state of the substance. In a solid, particles form a compact structure that resists flow. Particles in a liquid have more energy than those in a solid. They can flow past one another, but they remain close. Particles in a gas have the most energy. They move rapidly and are separated from one another by relatively large distances.


Copper (element), symbol Cu, brownish-red metallic element that is one of the most widely used of metals. Copper is one of the transition elements of the periodic table (see Periodic Law). The atomic number of copper is 29.

Copper was known to prehistoric people and was probably the first metal from which useful articles were made. Copper objects have been found among the remains of many ancient civilizations, including those of Egypt, Asia Minor, China, southeastern Europe, Cyprus (from which the word copper is derived), and Crete (KrĂ­ti). It was known to Native Americans, and American ores were found by the European explorers. It is also found in the pure state.


Copper melts at about 1083° C (about 1981° F), boils at about 2567° C (about 4753° F), and has a specific gravity of 8.9. The atomic weight of copper is 63.546.

Because of its many desirable properties, such as its conductivity of electricity and heat, its resistance to corrosion, its malleability and ductility, and its beauty, copper has long been used in a wide variety of applications. The principal uses are electrical, because of copper's extremely high conductivity, which is second only to that of silver. Because copper is very ductile, it can be drawn into wires of any diameter from about 0.025 mm (about 0.001 in) upward. The tensile strength of drawn copper wire is about 4200 kg/sq cm (about 60,000 lb/sq in); it can be used in outdoor power lines and cables, as well as in house wiring, lamp cords, and electrical machinery such as generators, motors, controllers, signaling devices, electromagnets, and communications equipment.

Copper has been used for coins throughout recorded history and has also been fashioned into cooking utensils, vats, and ornamental objects. Copper was at one time used extensively for sheathing the bottom of wooden ships to prevent fouling. Copper can easily be electroplated, alone or as a base for other metals. Large amounts are used for this purpose, particularly in making electrotypes, reproductions of type for printing.