Copper (Cu) is a transition metal with an atomic weight of 63.5, it has an electron configuration of [Ar] 3d10 4s1 enabling it to form oxidation states of +1 and +2. In its purest form it is a distinctive reddish-brown colour; however, once exposed to the atmosphere it slowly reacts forming a black oxide layer upon its surface. In solution, Copper has the ability to form ligands and depending on the ligand, the colour of the solution can change. For example, in water, copper is chemically known as a hexaaquacopper(II) ion, [Cu(H20)6]2+ . However, in the presence of Chloride ions, ligand exchange occurs and a tetrachlorocopper(II) ion, [CuCl4]2- .
It is mined as copper ores (mostly copper sulphides) which contain on average only 0.6% copper. It is commonly used in wiring because of its high thermal and electrical conductivity, as well as in pipe work as it is very ductile.