Copper (Cuprum) is a metal element and a transition element, with chemical symbol Cu, English copper and atomic number 29. Pure copper is a kind of soft metal. When it is just cut, its surface is reddish-orange with metallic luster, and its simple substance is purplish red.

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Cu2+ salt is the most common copper compound, and its hydrated ions are often blue, while chlorine as ligand is green. It is the source of the color of chalcocite and turquoise, and has been widely used as a pigment in history. Copper buildings will produce verdigris (basic copper carbonate) after corrosion. Decorative arts mainly use metallic copper and pigments containing copper.

Copper is one of the earliest metals used by human beings. As early as prehistoric times, people began to mine open-pit copper mines and use the obtained copper to make weapons, tools and other utensils. The use of copper had a far-reaching impact on the progress of early human civilization. Copper is a metal that exists in the earth's crust and ocean. The copper content in the crust is about 0.0 1%, and in some copper deposits, the copper content can reach 3% ~ 5%. Most of the copper in nature exists in the form of compounds, that is, copper ores.