Since we're now in chemistry class, it can be noted that "oxidation" doesn't necessarily involve a reaction with oxygen, although that's how it originally got that name. It's actually the loss of electrons from the oxidized atom to the other "reduced" atom, which may be oxygen, but also others such as chlorine.
Copper when oxidized by oxygen shows the colors exhibited by progressively older pennies, from the reddish-brown cuprous oxide(Cu(2)O)to the almost black cupric oxide(CuO). A greenish color on copper is the result of oxidation by chlorine to the chloride in the presence of moisture.
