What is Copper? Information on Copper element properties, symbol, What are the chemical, physical, mechanical, thermal properties?
COPPER; is a metallic element of great technological and historical importance. It is valued for its strength, malleability, ductility, corrosion resistance, and its ability to conduct electricity and heat. The metal is fairly abundant and has been used by man since prehistoric times for a wide variety of purposes, both by itself and as an alloy with other metals. In the ancient world copper was used for making tools and weapons, and the metal and its alloys have served as building and ornamental materials. Today copper is of importance in such diverse areas as electroplating, plumbing, and the manufacture of electric motors, television sets, airplanes, and satellites. Its compounds are important in agriculture and the chemical industry.
Properties
Copper is the 29th element in the periodic table; it has an atomic weight of 63.54 and is the first in the series of metallic elements that also contains silver and gold. Copper is a relatively heavy metal, with a specific gravity of 8.96. The pure element is salmon pink and has a bright metallic luster when polished. The metal is nonmagnetic, tough, and moderately hard, and it resists wear very well.
Chemical Properties.
A free atom of copper has an arrangement of electrons which can lead to the formation of a Cu+1 ion or a Cu+2 ion. A copper ion with a single electron removed is called a cuprous ion, while a copper ion with 2 electrons removed is called a cupric ion. The singly ionized cuprous ion occurs when an electron is removed from the outer electron shell of a copper atom, and the doubly ionized cupric ion results from the additional removal of an electron from an inner electron shell. (An unstable, triply ionized form of copper also occurs.) This difference in the way in which copper can be ionized accounts for the relatively different properties of chemical compounds of copper where different valences are involved. Removal of an electron from a free atom is often referred to as an oxidation reaction. For example, copper with 1 electron removed is said to be in a plus 1 oxidation state, while copper with 2 electrons removed is said to be in a plus 2 oxidation state. (The plus, in this case, refers to the sign of the charge on the ion involved.)
The chemical reactivity of copper in forming compounds involves both the plus 1 and the plus 2 oxidation states; chemical compounds of the plus 2 state are somewhat more stable than those of the plus 1 state. The chemical reaction of copper with basic solutions is minimal, except in the case of solutions containing ammonia. Copper is not replaced by hydrogen in acidic solutions, on the other hand, but it is easily dissolved in oxidizing acids such as nitric acid.
Within a copper crystal, the copper atoms are arranged in a face-centered cubic structure. As a result, each copper atom has 12 equidistant neighbors which are symmetrically distributed around the atom. This arrangement has the highest symmetry of any crystal structure in nature. The actual diameter of a single copper atom is about 2.5 angstrom units or 2.5 x 18 5 cm.
Electrical Conductivity.
One of the single most important properties of bulk copper is its very high electrical conductivity. This property accounts for the extensive use of copper in the electrical industry. The high electrical conductivity of copper is intimately associated with the fact that when free copper atoms are brought together to form bulk copper, the valence electrons of the copper are not restricted to their parent atoms but are free to migrate throughout the solid. On the basis of a unit volume, the electrical conductivity of copper (at room temperature) is exceeded only by the electrical conductivity of silver. Indeed, the electrical properties of copper are the basis of an international standard; the conductivity of a bar of copper 1 meter long and weighing 1 gram, at 20°C (68°F), is established as 100% conductivity. Even so, modern purification techniques easily produce a grade of copper which is 4% to 5% higher in conductivity than this standard.
Thermal Conductivity.
Another important consequence of the presence of free electrons in the solid is the very high thermal conductivity of copper, again only exceeded by the thermal conductivity of silver. Many of the extensive commercial applications of copper rely upon this high thermal conductivity. Some of these are refrigerators, evaporators, heating coils, and distilling apparatus in the chemical industry, in which high thermal conductivity is required.
Mechanical Properties.
Many of the industrial operations involved in the formation of copper into usable shapes involve extensive plastic (permanent) deformation of the metal. Copper, in contrast to iron, can be deformed in this manner —even at temperatures approaching absolute zero—without any serious loss of ductility. This is quite important, since the final forming operation of many products does not require heating the copper during the operation. Heating, if required, would seriously discolor the product. Also, copper would tend to oxidize when heated, and would be seriously embrittled.
The mechanical properties of copper vary over a wide range, depending strongly on the past history of the material. For example, extensive plastic deformation of single copper crystals starts at stresses as low as 15 psi (1 kg per sq cm) in polycrystalline copper, plastic deformation is initiated at 500 psi (35 kg per sq cm). Extensive cold-working of copper can introduce a further increase in the yield stress to a value of 10,000 psi (more than 700 kg per sq cm). However, in contrast to iron, copper shows extensive plastic deformation after extreme reductions in cross-sectional area. In fact, in wire drawing of copper, the material is often reduced to less than 1% of its original diameter.
Cold-worked copper can be annealed at temperatures as low as 392°F (200°C); extensive softening of the material occurs. Annealing at progressively higher temperatures leads to additional softening of the deformed material. Complete softening is reached at temperatures of about 1200°F (650°C).
Another important property of copper which lends itself to commercial use is its corrosion resistance, and especially its resistance to oxidation while carrying water. Furthermore, copper tubing, when used for carrying water, does not pick up a mineral deposit (as does iron pipe under similar circumstances). This accounts for the extensive use of copper for making water pipes and water valves and other fittings used in superior plumbing installations. On the other hand, the familiar corrosion product that appears on copper statuary is considered a highly desirable protective coating. This coating, or patina, is a mixture of the basic copper sulfates CuSO4 . Cu(OH)2 and CuSO4 • 3Cu(OH)2.
