The name is derived from the Latin cuprum, "copper," from the earlier Latin Cyprium, "Cyprian metal." The discovery of the metal dates from prehistoric times, and it is estimated that copper was first used about 5000 BC or even earlier. In Roman times much of the copper was obtained from the island of Cyprus, as the name implies. Copper today is mined in many parts of the world, the largest producers at present being Chile, Peru, Poland, the United States, Zaire, and Zambia.
More than 160 minerals containing copper are known. Copper constitutes 70 parts per million of the Earth's crust and is present to the extent of 0.020-0.001 parts per million in seawater. In its native state such as that found in the Lake Superior region of North America it is often so pure that it requires only melting with a flux to produce "lake copper," which for many years was the world standard for pure copper. About 80% of all copper mined today, however, is derived from low grade ores containing 2% or less of the element. Half of the world's copper deposits are in the form of chalcopyrite ore. All important copper-bearing ores fall into two main classes: oxidized ores and sulfide ores.
Sulfide ores are more important commercially. Ores are removed either by open-pit or by underground mining. Ores containing as little as 0.4% copper can be mined profitably in open-pit mining, but underground mining is profitable only if an ore contains 0.7%-6% copper. The oxidized ores, such as cuprite and tenorite, can be reduced directly to metallic copper by heating with carbon in a furnace, but the sulfide ores, such as chalcopyrite and chalcocite, require a more complex treatment in which low-grade ores have to be enriched before smelting begins. This involves the ore-flotation process, in which the ore is crushed and powdered before it is agitated with water containing a foaming agent and an agent to make the copper bearing particles water-repellent. These particles accumulate in the froth on the surface of the flotation tank, and this froth is skimmed off and heated to about 800 deg C to remove some of the water as well as antimony, arsenic, and sulfur, which are also present. The residue is then mixed with silica and melted in a furnace at 1,400 deg 1,500 deg. C. This produces two liquid layers: a lower layer of copper matte (cuprous sulfide mixed with iron sulfide and oxides), and an upper layer of silicate slag, which is drawn off. Silica or siliceous copper ore is added to the liquid matte in a converter, and air under pressure is blown through the liquid. Upon removal of the iron slag, the copper(I) sulfide that remains is reduced to copper by heating in a controlled amount of air. The remaining molten copper, which is 98%- 99% pure, is either cast into blocks of blister copper or into anodes. The final stage of purification is mainly by electrolytic refining, which yields copper of 99.95% - 99.97% purity. The impure copper is made the anode of an electrolytic cell that contains pure strips of copper as the cathode and an electrolyte of aqueous copper (II) sulfate. During electrolysis, copper is transferred from the anode to the cathode. An anode sludge containing silver and gold is produced during this process, and this increases its economic feasibility.
Eleven isotopes of copper are known, two of which are not radioactive and occur with a natural abundance of 69.09% and 30.91%, respectively. Copper melts at 1,083.4 deg plus or minus 0.2 deg C (in a vacuum), boils at 2,567 deg C, and has a density of 8.96 at 20 deg C. The element has a hardness of 3, takes on a bright metallic luster, has a cubic crystal structure, and is malleable, ductile, and a good conductor of heat and electricity, second only to silver in electrical conductivity. Copper exhibits oxidation states of +2 (the most common, forming Cu (II) compounds), and + 1 (Cu(I), stable only in aqueous solution if part of a stable complex ion); a few compounds of copper (III) are also known. Although the electronic configuration of copper is formally similar to that of the alkali metals (Group IA) in general and potassium in particular, the behavior of copper is considerably different from that of the alkali metals. The shielding of the outer electron from the attraction of the nucleus is stronger than in copper. Thus the outer electron in copper is more tightly bound, resulting in a comparatively high first ionization potential and a relatively small ionic radius for copper. The outstanding feature of copper and the other metals of Group IB (gold and silver ) is their resistance to chemical attack. Copper is slowly attacked by moist air, and its surface gradually becomes covered with the characteristic green patina that consists of basic sulfate. At about 300 deg C copper is attacked by air or oxygen, and a black coating of copper(II) oxide forms at the surface; at a temperature of 1,000 deg C copper(I) oxide is formed instead. The metal is attacked by sulfur vapor, with the formation of copper (I) sulfide; and by the halogens, which form copper (II) halides, except iodine, which forms copper (I) iodide. When copper is not attacked by water or steam, and dilute nonoxidizing acids, such as dilute hydrochloric and dilute sulfuric acids, have no effect in the absence of an oxidizing agent. The metal is attacked by boiling concentrated hydrochloric acid with the evolution of hydrogen, by hot concentrated sulfuric acid, and by dilute or concentrated nitric acid.