Copper, silver, and gold have been chosen as currency for so long because they are durable and they do not readily react with many other materials. They generally do not oxidize in air, unless it is particularly moist in copper's case. These metals also display high levels of the physical properties of metals; copper, silver, and gold are all particularly malleable, ductile and are also good conductors.These metals use their d orbital in chemical bonding, just like other transition metals and so they exist in several oxidation states, which can be seen in the table listing several of the properties of the coinage metals. They can also form complex ions and demonstrate paramagnetism.
Silver does oxidize. However, it usually doesn't harm the metal any, just like a tarnishing. I had to google the term "Group 11" and came up with this interesting article. http://en.wikipedia.org/wiki/Group_11_element
Nowadays, it feels like all money is this Group 11 metal: http://en.wikipedia.org/wiki/Roentgenium It disappears quickly.
