<P> Copper is a soft metal (MH 2.5--3.0) with low mechanical strength . It has a close - packed face - centred cubic structure (BCN 12). Copper behaves like a transition metal in its preferred oxidation state of + 2 . Stable compounds in which copper is in its less preferred oxidation state of + 1 (Cu O, CuCl, CuBr, CuI and CuCN, for example) have significant covalent character . The oxide (CuO) is amphoteric, with predominating basic properties; it can be fused with alkali oxides (M O; M = Na, K) to give anionic oxycuprates (M CuO). Copper forms Zintl phases such as Li CuSi and M Cu Sb (M = Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, or Er). </P> <P> Silver is a soft metal (MH 2.5--3) with low mechanical strength . It has a close - packed face - centred cubic structure (BCN 12). The chemistry of silver is dominated by its + 1 valence state in which it shows generally similar physical and chemical properties to compounds of thallium, a main group metal, in the same oxidation state . It tends to bond covalently in most of its compounds . The oxide (Ag O) is amphoteric, with basic properties predominating . Silver forms a series of oxoargentates (M AgO, M = Na, K, Rb). It is a constituent of Zintl phases such as Li AgM (M = Al, Ga, In, Tl, Si, Ge, Sn or Pb) and Yb Ag . </P> <P> Gold is a soft metal (MH 2.5--3) that is easily deformed . It has a close - packed face - centred cubic structure (BCN 12). The chemistry of gold is dominated by its + 3 valence state; all such compounds of gold feature covalent bonding, as do its stable + 1 compounds . Gold oxide (Au O) is amphoteric, with acidic properties predominating; it forms anionic hydroxoaurates M (Au (OH)) where M = Na, K, ​ ⁄ Ba, Tl; and aurates such as NaAuO . Gold is a constituent of Zintl phases such as M AuBi (M = Li or Na); Li AuM (M = In, Tl, Ge, Pb, Sn) and Ca Au . </P> <P> On the group 12 transition metals (zinc, cadmium and mercury), Smith observed that, "Textbook writers have always found difficulty in dealing with these elements ." There is an abrupt and significant reduction in physical metallic character from group 11 to group 12 . Their chemistry is that of main group elements . A 2003 survey of chemistry books showed that they were treated as either transition metals or main group elements on about a 50 / 50 basis . The IUPAC Red Book notes that although the group 3 − 12 elements are commonly referred to as the transition elements, the group 12 elements are not always included . The group 12 elements do not satisfy the IUPAC Gold Book definition of a transition metal . </P>

Key physical difference between transition metals and poor metals