Why is copper useful?
Copper has many uses as a metal, in alloys and in ionic compounds. Much of copper's usefulness is due to it's metallic properties. It's a very good electrical conductor, second only to silver. it's malleable and ductile and doesn't corrode easily.
The most common use of copper is for electrical wiring. It's used for this purpose in buildings, in electrical transmission lines and in electric motors. Its conductivity and ductility (ability to be drawn into a wire) make it useful for this purpose.
Another common use of copper is for water pipes in buildings. It's less reactive than hydrogen so it doesn't react with water. Plastics have started replacing copper for this purpose due to its cost.
Copper is used to make U.S. pennies, although they now have only a thin layer of copper over a zinc core. It's also used for jewelry, cookware, architectural elements and decorative items. Copper is one of the oldest metals to be used by humans. It's easily worked due to its malleability When used outdoors it develops an attractive turquoise-colored oxide that protects it from further oxidation.
Alloys of copper such as brass and bronze are used for musical instruments. Disrupting the metallic crystal structure with another size of atom improves the resonance of the material. Copper alloys have other uses as well because of their strength and corrosion resistance.
Copper's antimicrobial property makes its ionic compounds useful as algaecides and bacteria inhibitors.