Discovery, properties and applications of chromium and its compounds

The basic properties of chromium are described, subsequently the discovery of chromium ores and the various methods of producing metallic chromium. How native chromium is formed and why the gemstone ruby has a connection to chromium are the following topics. The coordination of tri- and hexavalent chromium, hydrate isomerism, crystal field theory of Cr-III and chromium(III)-containing polyoxotungstates as well as two fascinating redox reactions (breathalyzer, chemical volcano) are presented in the next sections. Then the focus is directed to various applications of metallic chromium and its compounds (metallurgy, dyes and pigments, wood preservatives, foundry, catalysis, tanning, interconnectors for SOFC). In conclusion, chromium's biological role and environmental concerns are discussed.