Chromium
Definition and meaning of Chromium in chemistry.
Chromium is a chemical element with the symbol Cr and atomic number 24. It is a steely-gray, lustrous, hard, and brittle transition metal that takes a high polish and resists tarnishing.
In more detail
Chromium is the first element in group 6 of the periodic table and is renowned for its exceptional magnetic properties, being the only elemental solid that exhibits antiferromagnetic ordering at room temperature. It primarily occurs in the mineral chromite, from which it is extracted commercially. The element demonstrates a complex chemistry characterized by a wide range of oxidation states, with +3 and +6 being the most stable and common, though +2 is also frequently observed. Hexavalent chromium compounds, such as chromates (CrO4 2-) and dichromates (Cr2O7 2-), are powerful oxidizers and are known to be highly toxic and carcinogenic. Trivalent chromium is considered an essential trace element in humans, playing a role in lipid and sugar metabolism, although its exact mechanism remains a subject of ongoing research. In addition to its metallurgical applications, chromium compounds are widely used as pigments to impart brilliant green, yellow, and red colors to paints and glass.
Key facts
| Field | General Chemistry |
|---|---|
| Symbol | Cr |
| Atomic number | 24 |
| Atomic mass | 51.996 u |
| Category | Transition Metal |
| State at room temperature | Solid |
| Melting point | 1907 °C |
| Boiling point | 2671 °C |
| Year discovered | 1797 |
Chromium is heavily used in the production of stainless steel, where the addition of at least 11 percent chromium by mass prevents the steel from rusting.
Frequently asked questions
Why is chromium used in electroplating?
Chromium is used in electroplating because it provides a hard, beautiful surface finish that is highly resistant to corrosion and tarnishing.
What is the difference between trivalent and hexavalent chromium?
Trivalent chromium is a stable, naturally occurring form that is generally considered safe and potentially essential, whereas hexavalent chromium is a toxic, anthropogenic compound that is a known carcinogen.