Symbol Cu A ductile, malleable, reddish-brown metallic element that is an excellent conductor of heat and electricity and is widely used for electrical wiring, water piping, and corrosion-resistant parts, either pure or in alloys such as brass and bronze. Atomic number 29; atomic weight 63.54; melting point 1,083°C; boiling point 2,595°C; specific gravity 8.96