Copper is a chemical element with the symbol Cu (Latin: cuprum) and atomic number 29. It is a ductile metal, with very high thermal and electrical conductivity. Pure copper is rather soft and malleable, and a freshly exposed surface has a reddish-orange color. It is used as a thermal conductor, an electrical conductor, a building material, and a constituent of various metal alloys.
Copper metal and alloys have been used for thousands of years. In the Roman era, copper was principally mined on Cyprus, hence the origin of the name of the metal as Cyprium, “metal of Cyprus”, later shortened to Cuprum.
There may be insufficient reserves to sustain current high rates of copper consumption. Some countries, such as Chile and the United States, still have sizeable reserves of the metal which are extracted through large open pit mines.
Copper compounds are commonly encountered as salts of Cu2+, which often impart blue or green colors to minerals such as turquoise and have been used historically widely as pigments. Copper metal architectural structures and statuary eventually corrode to acquire a characteristic green patina. Copper as both metal and pigmented salt, has a significant presence in decorative art.
Copper(II) ions (Cu2+) are soluble in water, where they function at low concentration as bacteriostatic substances, fungicides, and wood preservatives. In sufficient amounts, copper salts can be poisonous to higher organisms as well. However, despite universal toxicity at high concentrations, the Cu2+ ion at lower concentrations is an essential trace nutrient to all higher plant and animal life. In animals, including humans, it is found widely in tissues, with concentration in liver, muscle, and bone. It functions as a co-factor in various enzymes and in copper-based pigments.
Copper occupies the same family of the periodic table as silver and gold, since they each have one s-orbital electron on top of a filled electron shell which forms metallic bonds. Like silver and gold, copper is easily worked, being both ductile and malleable. The ease with which it can be drawn into wire makes it useful for electrical work as does its excellent electrical conductivity. Copper is normally supplied, as with nearly all metals for industrial and commercial use, in a fine grained polycrystalline form. Polycrystalline metals have greater strength than monocrystalline forms, and the difference is greater for smaller grain (crystal) sizes.
Copper just above its melting point keeps its pink luster color when enough light outshines the orange incandescence color.
Comparison between unoxidized copper wire (left) and normal oxidized copper (right).
Copper has a reddish, orangish, or brownish color owing to a thin layer of tarnish (including oxides). Pure copper, is pink- or peach-coloured. Copper, osmium (blueish) and gold (yellow) are the only three elemental metals with a natural color other than gray or silver. Copper’s characteristic color results from its band structure: copper is the exception to Madelung’s rule, with only one electron in the 4s subshell instead of two. The energy of a photon of blue or violet light is sufficient for a d band electron to absorb it and transition to the half-full s band. Thus, the light reflected by copper is missing some blue/violet components and appears red. This phenomenon is exhibited by gold which has a corresponding 5s/4d structure. Liquid copper appears somewhat greenish, a characteristic shared with gold in the absence of bright ambient light.
Crystals of native copper 12 × 8.5 cm.
Copper can be found as native copper in mineral form (for example, in Michigan’s Keweenaw Peninsula). It is a polycrystal, with the largest single crystals measuring 4.4×3.2×3.2 cm. Minerals such as the sulfides: chalcopyrite (CuFeS2), bornite (Cu5FeS4), covellite (CuS), chalcocite (Cu2S) are sources of copper, as are the carbonates: azurite (Cu3(CO3)2(OH)2) and malachite (Cu2CO3(OH)2) and the oxide: cuprite (Cu2O).
Copper is found in a variety of enzymes and proteins, including the cytochrome c oxidase and certain superoxide dismutases. Copper is used for biological electron transport, e.g. the blue copper proteins azurin and plastocyanin. The name “blue copper” comes from their intense blue color arising from a ligand-to-metal charge transfer (LMCT) absorption band around 600 nm. Most molluscs and some arthropods such as the horseshoe crab use the copper-containing pigment hemocyanin rather than iron-containing hemoglobin for oxygen transport, so their blood is blue when oxygenated rather than red.
info soure: wikipedia