Copper is in group 11 on the periodic table, along with silver and gold. There is also one other element that theoretically belongs in this group, roentgenium, which has a half life of 26 seconds and has only ever been formed under laboratory conditions.
This group of precious metals is sometimes referred to as the coinage metals, as they have a number of properties that have made them popular for use in money throughout history. Some of these properties include their durability, resistance to tarnishing and the fact that they can easily be identified. The fact that they are hard to counterfeit is another reason they have often been used for coins.