Some general properties

Copper : The Element

Copper is a first row transition metal at the head of group IB in the periodic table. It is a reddish brown colour. It is estimated that copper was first used about 5000 BC. The word copper is derived from the latin cuprum. There are more than 160 minerals containing copper known to man, and copper constuties 70 parts per million of the earths crust and 0.020-0.001 parts per million in sea water. Copper is used in alloys such as brass, and is completely miscible with gold.

Although Copper has a single 4s 1 electron it has very little in common with the alkalis metals, except for the formal stoichiometries in the +1 oxidation state. The first ionization energy is lower than that of the alkalis metals because the 3d shell is alot less effective at sheilding the s electron from the nuclear charge than is a noble gas shell. The melting point and sublimation point are also higher than for the alkalis metals because the 3d electrons are involved in metalic bonding. These factors give the element some noble character. This gives the element its covalent characterwhich is not offset by the smaller radius of Cu⁺.The second and third ionization energies are lower than the alkalis metals and this in part accounts for the transition metal character.

Copper redily dissolves in nitric acid, and in sulphuric acidin the presence of oxygen.

Copper (1) and its chemistry

Cu¹ is Tetrahydral as in Cu1(s) or [Cu(CN)₄]^3- and Square Planer for CuO(s), [Cu(py)₄]²⁺ or [CuCl₄]^2-. Copper(1) compouds are diamagnetic and are colourless except when the colour resylts from the anion or charge transfer bands.

The relative stabilities of the Cu^I and Cu^IIare indicated by there potentials:

In aqueous solution only low equilibrium concentrations of Cu⁺ <(<10^-2M)can exist.The only Cu(1)compounds that are stable to water are the high insoluble ones such as CuCl or CuCN.This instability to water is due partly to the greater lattice and solvent energies and higher formation constants for complexes of the Cu²⁺ ion so that ionic Cu(1) derivatives are unstable.

The equilibrium 2 Cu^I <=====>Cu + Cu^II can readily be displaced in either direction. Thus, with Cn^-, I^- and (CH₃)₂S, Cu^II reacts to give the Cu^I compound. The Cu^II state is favoured by anions that cannot give covalent bonds or bridging groups of by complexing agents that have their greater affinity for Cu^II. Thus ethyllenediamine reacts with copper(I) chloridein aqueous potassium chloride solution.

The lifetime of the Cu⁺ ionin water is usally very short (<1 s). An excellent illustration of how the stability of the Cu^I ion relative to that of the Cu^II ion may be affected by the solvent is the case of acetonitrile. The Cu^I ion is very effectively solvated by CH₃CN , and the halides have relatively high solubilites (eg CuI, 35g/kg CH₃CN) Versus negligible solubilites in H₂O. The Cu^I ion is more stable than Cu^II in CH₃CN, and Cu^II acts as a comparatively powerful oxidizing agent.

Copper (II) and its chemistry

Most Cu^I compounds are fairly readily oxidised to Cu^II, but further oxidation to Cu^III is difficult. There is a well defined aqueous chemistry of Cu²⁺, as a large number of salts of various anions, many of which are water soluble, that exist in addition to a wealth of complexes.

Cu^II has a d⁹ configuration. This has an effect on the stereo chemistry of it. It gives it distortion if placed in an enviroment of cubic symmmetry. The result is that Cu^II is nearly always found in enviroments appreciably distorted from these regular symmetries. the characteristic distortion of an the octahydron is that there are 4 short Cu--L bonds in the planeand two trans long ones.

Catalytic properties of copper compounds

Copper compounds catalyze an exceedingly varied array of reactions, heterogeneously, homogeneously, inthe vapour phase, in organic solvents, and in aqueous solution. Many of these reactions, particuarly in aqueous soloution, involve oxidation--reduction systems and a Cu^I--Cu^II redox cycle. Molecular oxygen can often be utilized as an oxidant, for example in the copper catylized oxidations of ascorbic acid.

The oxidation probably involves an inital oxidative addition reaction

Copper compounds have many uses in organic chemistry for oxidations, for example of Penols by Cu²⁺ - amine complexes, halogenations, coupling reactions, and the like.

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