History and Discovery
Chromium is a chemical element with the symbol Cr and atomic number 24. It is a hard, silver-white, and hard metal with a shiny appearance. The element was discovered in 1797 by the French chemist Nicolas-Louis Vauquelin in the mineral crocoite (lead(II) chromate) found in the Ural Mountains. Vauquelin isolated the metal by reducing the oxide with carbon. The name "chromium" comes from the Greek word "chroma," meaning color, as the metal was initially used as a pigment in glass.
Physical and Chemical Properties
Chromium is a transition metal and belongs to the d-block of the periodic table. It has a density of 7.14 g/cm³ at 20 °C and a melting point of 1907 °C. The element has a wide range of allotropes, with chromium(III) oxide (Cr2O3) being the most stable. Chromium has a low reactivity with air at room temperature, but it burns in air at high temperatures, forming chromium(III) oxide. The element has a hexagonal crystal structure with a lattice parameter of 2.88 Å.
Chromium is highly resistant to corrosion due to the formation of a thin oxide layer on its surface. However, the element can react with halogens, acids, and bases to form various compounds. Chromium(III) chloride (CrCl3) is a common compound used as a catalyst in organic reactions. Chromium(II) chloride (CrCl2) is used as a reducing agent in organic chemistry.
Occurrence and Production
Chromium is a relatively rare element, making up about 0.006% of the Earth's crust. It is primarily found in the minerals chromite (FeCr2O4) and crocoite (PbCrO4). The largest producers of chromium are South Africa, India, and Kazakhstan, which account for over 90% of global production.
The primary method of chromium production involves the roasting of chromite ore to form chromite (FeCr2O4). The ore is then reduced with aluminum and silicon to produce chromium metal. The metal is further purified through electrolysis to produce high-purity chromium.
Applications and Uses
Chromium has a wide range of applications due to its unique properties. The element is used in the production of stainless steel, which contains 10-20% chromium. The addition of chromium to steel improves its corrosion resistance and durability. Chromium is also used in the production of chrome plating, which is used to protect surfaces from corrosion and wear.
Chromium is used in the production of catalytic converters in vehicles, which reduce emissions of nitrogen oxides and carbon monoxide. The element is also used in the production of leather tanning agents, which improve the strength and water resistance of leather.
Environmental and Health Concerns
Chromium has been linked to several environmental and health concerns. The element can accumulate in the environment and contaminate soil and water. Chromium(VI) compounds are toxic and carcinogenic, and have been linked to various health problems, including lung cancer and respiratory problems.
The production of chromium has also been linked to environmental concerns, including air and water pollution. The mining and processing of chromite ore can release toxic chemicals into the environment, which can have devastating effects on local ecosystems.
The use of chromium in tanning agents has also been linked to environmental concerns, including the contamination of waterways and soil. The element can also accumulate in the food chain, posing a risk to human health.
References
- Vauquelin, N. L. (1797). "Memoire sur un Nouveau Corps de la Famille des Terres Acides." Journal de Physique, 34, 170-175.
- Greenwood, N. N., & Earnshaw, A. (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann.
- CRC Handbook of Chemistry and Physics (98th ed.). Boca Raton, FL: CRC Press.
- "Chromium." International Trade Centre. Retrieved from <https://www.intracen.org/chromium/>
- "Chromium." United States Environmental Protection Agency. Retrieved from <https://www.epa.gov/chromium>
- "Chromium." World Health Organization. Retrieved from <https://www.who.int/news-room/fact-sheets/detail/chromium>