Cobalt Group: Elements of the Ninth Subgroup

This chapter describes the properties, occurrences, manufacturing processes, and applications of the elements of the ninth subgroup of the periodic table (cobalt, rhodium, iridium, meitnerium) with their most important compounds. Cobalt was discovered in 1735, rhodium and iridium at the beginning of the 19th century. The first atoms of meitnerium were produced in 1982. The effect of the lanthanide contraction can also be observed in rhodium and Iridium. The respective physical properties of these two elements differ significantly, but their chemical properties hardly differ. The properties of cobalt, on the other hand, differ significantly from those of the two “noble” platinum metals rhodium and iridium, as cobalt shows a negative standard potential as well as lower densities, melting and boiling points. For cobalt, the oxidation state +2 is the most stable, for rhodium +3, and for iridium +4. Recently, the production of iridium-VIII and IX compounds has been successful. Cobalt compounds have long been used in heat-resistant pigments and for painting porcelain and ceramics. Cobalt, as a component of steels, increases their wear and heat resistance. Its magnetic properties determine its use in data storage devices. Rhodium is mainly found in catalysts and jewelry items. The global demand for the precious metal iridium has increased significantly in recent years, partly due to new production methods in the electronics industry. It is used in spark plugs for engines used in aerospace, as well as in some catalysts for chemical syntheses. Meitnerium does not occur naturally and is only accessible through artificial means by nuclear fusion.