What is interesting about copper's electron configuration is that one electron is taken from the 4s shell and given to the 3d shell to complete it. According to the rules of filling electron shells, copper should have a configuration of 1s2 2s2 2p6 3s2 3p6 4s2 3d9 instead, but it does not. The unpaired 4s electron allows copper to attract a magnetic field.
Copper ions usually exists in either the +1 or +2 forms. The +2, or cupric, ion is more stable than the +1 cuprous ion. Generally, copper is not a very reactive element and can be found existing in its free elemental form in nature.
