The reactivity of the metals

   In general, the metals are moderately reactive and combine to give binary compounds when heated with dioxygen, sulfur or the halogens (e.g. reactions 1.1–1.3), product stoichiometry depending, in part, on the available oxidation states (see below).

                                                                    (1.1)

                                                                       (1.2)

             (1.3)

     Most d-block metals should, on thermodynamic grounds liberate H₂ from acids but, in practice, many do not since they are passivated by a thin surface coating of oxide or by having a high dihydrogen overpotential, or both. Silver, gold and mercury (i.e. late, second and third row metals) are, even in the thermodynamic sense, the least reactive metals known. For example, gold is not oxidized by atmospheric O₂ or attacked by acids, except by a 3 :1 mixture of concentrated HCl and HNO₃ (aqua regia).