The copper wire used in electrical wiring is a pure substance. It has identical atoms that cannot be separated through chemical means. Copper wires should have a very high level of purity for efficient conductivity; copper wires sold in stores have a 99.99 percent purity.
Copper is extracted from copper ores by roasting the ores in a series of furnaces with air and silicon dioxide. Then, the copper is put through a carbon reduction, followed by electrolysis, which purifies the copper, making it a good conductor of electricity. Copper reacts with oxidizing agents. When it is exposed to air, it forms a green patina that provides a natural protection against weathering and corrosion.