Copper is a chemical element; it has symbol Cu (from Latin cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orange color. Copper is used as a conductor of heat and electricity, as a building material, and as a constituent of various metal alloys, such as sterling silver used in jewelry, cupronickel used to make marine hardware and coins, and constantan used in strain gauges and thermocouples for temperature measurement.
Copper is one of the few native metals, meaning metals that occur naturally in a directly usable, unalloyed metallic form. This led to very early human use in several regions, from c.8000 BC. Thousands of years later, it was the first metal to be smelted from sulfide ores, c.5000 BC; the first metal to be cast into a shape in a mold, c.4000 BC; and the first metal to be purposely alloyed with another metal, tin, to create bronze, c.3500 BC.
Commonly encountered compounds are copper(II) salts, which often impart blue or green colors to such minerals as azurite, malachite, and turquoise, and have been used widely and historically as pigments.
Copper used in buildings, usually for roofing, oxidizes to form a green patina of compounds called verdigris. Copper is sometimes used in decorative art, both in its elemental metal form and in compounds as pigments. Copper compounds are used as bacteriostatic agents, fungicides, and wood preservatives.
Copper is essential to all aerobic organisms. It is particularly associated with oxygen metabolism. For example, it is found in the respiratory enzyme complex cytochrome c oxidase, in the oxygen carrying hemocyanin, and in several hydroxylases. Adult humans contain between 1.4 and 2.1mg of copper per kilogram of body weight.