Copper, silver and gold, situated in group 11 of the periodic table, are known collectively as the coinage metals, and are characterized by their general resistance to corrosion. Copper is the most reactive, gold the least.
All three are resistant to attack by oxygen, although copper oxidizes at red heat. Both copper and silver react with sulphurous gases present in the atmosphere: silver acquires a black coating of silver sulphide, and copper a green coating of a basic sulphate (eggs, which contain sulphur, rapidly tarnish silver). Gold, however, does not react in such a way.
The three are resistant to attack by many acids, but copper and silver dissolve in nitric acid and hot concentrated sulphuric acid, and gold dissolves in aqua regia. Gold will also dissolve in solutions of some halogens.
All three metals are excellent conductors of heat and electricity. Silver is the best conductor of all the chemical elements, copper the second, and gold the third. They are also characterized by their great malleability and ductility. Gold is the most malleable and ductile of all metals, and silver the next.
Each member of the group has a characteristic colour: copper is reddish-brown; silver brilliant white; and gold a bright yellow.
