Copper subgroup physical properties

Copper, silver and gold are soft lustred metals. Copper is red, gold has yellow colour. These metals are ductile that can be easily rolled and form very thin wire and foil (Au can be rolled to foil of the thickness about 0.2 m and 1g of Au can be transformed to wire of the length 2 km!).

Metals of copper subgroup have high electric and thermal conductivity.

Silver has lower melting and boiling points comparing with Cu and Au and it is the most electro- and thermally conductive metal simultaneously. These facts are explained by the unique stability of completely filled 4d orbital. The single valence electron of Ag is not capable to penetrate through it. It is this stability that the most stable oxidation state of Ag is +1.

All three have been used for making coins. Hence they are often named collectively the coinage metals. Copper subgroup elements are constituents of various metal alloys. Of great practical importance are bronzes (90% Cu, 10% Sn),  tombac (90% Cu, 10% Zn), cupronickel [мельхіор] (68% Cu, 30% Ni, 1% Mn, 1% Fe), German silver [нейзильбер] (65% Cu, 20% Zn, 15% Ni), brass [латунь] (60% Cu, 40% Zn), and also coin alloys (95% Cu, 5% Al – 5 copecs coins in the former USSR, 80% Cu, 20% Ni in 10 copecs coins and more).

Copper subgroup trends

	Cu	Ag	Au
density, g/сm3	8.94	10.5	19.3
tm, oС	1084	961	1047
tb, oС	2600	2210	2970
Rа, nm	0.123	0.144	0.144
radius Е+, nm	0.096	0.116	0.137
Ionisation energy Е ® Е+, еV
Еo(Е3+ + 3е = Е), V	+0.340	+0.799	+1.500
	Cu2+/Cu	Ag+/Ag	Au3+/Au

History of discovery

Copper is the part of many legends, such as that of Iraq's Baghdad Battery. Copper cylinders soldered to lead, which date back to 248 B.C. to 226 A.D, resemble a galvanic cell, leading people to believe this may have been the first battery. This claim has so far not been substantiated.

The Bible also refers to the importance of copper: "Men know how to mine silver and refine gold, to dig iron from the earth and melt copper from stone" .

In alchemy the symbol for copper, perhaps a stylized mirror, was also the symbol for the goddess and planet Venus.

In the Roman era, copper was principally mined on Cyprus, hence the origin of the name of the metal as Cyprium, "metal of Cyprus", later shortened to Cuprum.

The Sun symbol has long represented gold

	Cu	Ag	Au
Content in the Earth crust, %(mol.)	3×10-3	2×10-6	5×10-8

All elements are encountered in nature in the free state (the largest nuggets: Cu - 420 t, Ag - 13,5 t, Au - 153 kg). Sulfides are the most important minerals of copper and provide about 90% of world output of this metal. Sulfide ores of copper: chalcopyrite (CuFeS₂), bornite (Cu₅FeS₄), covellite (CuS), chalcocite (Cu₂S). Carbonate ores are azurite (Cu₃(CO₃)₂(OH)₂), malachite (Cu₂CO₃(OH)₂), and the oxide cuprite (Cu₂O).

Silver and gold are rare elements. Minerals of silver combined with sulfur, arsenic, antimony or chlorine are argentite (Ag₂S), horn silver (AgCl), and pyrargyrite (Ag₃SbS₃). They are of little importance because silver is predominately mined in native form or alloyed with gold. The content of silver in industrially important ores makes up usually 50-350 g∙t^-1. The principal sources of silver are the ores of copper, copper-nickel, lead, and lead-zinc obtained from Peru, Mexico, China, Australia, Chile, Poland and Serbia. Peru and Mexico have been mining silver since 1546 and are still major world producers.

Gold appears most often as a solid solution with silver, i.e. a gold silver alloy. Such alloys usually have a silver content of 8–10%. Electrum is an alloy of gold with more than 20% silver. Electrum's colour runs from golden silvery to silvery, dependent upon the silver content. The more silver, the lower the specific gravity. Gold sometimes occurs combined with tellurium as the minerals calaverite(AuTe₂), krennerite(orthorhombic AuTe₂ varying to Au_0.8,Ag_0.2Te) and as the rare bismuthide maldonite (Au₂Bi) and antimonide aurostibite (AuSb₂).

Recent research suggests that microbes can sometimes play an important role in forming gold deposits, transporting and precipitating gold to form grains and nuggets that collect in alluvial deposits