cR

Cr is a chemical element with the symbol Cr and atomic number 24. It is a transition metal in the periodic table known for its hardness, high melting point, and the ability to form a stable, protective oxide layer that passivates its surface, contributing to the corrosion resistance of stainless steels and other alloys.

Chromium occurs naturally mainly in chromite (FeCr2O4) and is produced commercially by reducing chromite to ferrochromium and then refining to metal. The element has a variety of oxidation states, with +3 and +6 being the most common. Cr(VI) compounds, such as chromates and dichromates, are highly oxidizing and toxic, and their use is tightly regulated in industrial processes. Cr(III) salts are less toxic and are sometimes discussed as having nutritional importance in trace amounts, though the essentiality of chromium in humans remains a topic of ongoing research and debate.

Common uses of chromium include stainless steel production, chrome plating, and pigments. Chromium oxide (Cr2O3) provides durable green pigments and is used in ceramics and refractories. Chromium compounds have historically been employed as dyes and catalysts in various industrial processes, though environmental and health considerations have shifted many applications toward more regulated and safer alternatives.

Chromium was discovered in 1797 by Louis Nicolas Vauquelin and named from the Greek word chroma, meaning color, in reference to the colorful compounds it forms. Safety concerns center on Cr(VI) compounds, which require careful handling, containment, and compliance with occupational exposure standards to limit health risks.