Chromium is a transition metal that was discovered by Gottlob Lehmann in 1766. It has a shiny surface that is resistant to corrosion and this quality makes its ideal for manufacturing and coating of wide range of material, including cars and bikes.
History and Discovery
Chromium was initially discovered in red crystalline mineral form, known Siberian red lead, by Johann Gottlob Lehmann (1766). Later, chromium was discovered as a novel, and isolated metal by Louis-Nicolas Vauquelin in 1797. The name chromium has been derived from Greek word, chroma, which means color. The name was given to this metal as it exists in diverse colors and was suggested by, Antoine Francois de Fourcroy (1755-1809) and René-Just Haüy (1743-1822). Chromium has a distinct shine and forms various compounds in different colors that include green, purple, black, yellow, and orange .
|Periodic Table Classification||Group 6
|State at 20C||Solid|
|Electron Configuration||[Ar] 3d5 4s1|
|Electron Shell||2, 8, 13, 1|
|Density||7.19 g.cm-3 at 20°C|
|Atomic Mass||51.99 g.mol -1|
|Electronegativity according to Pauling||1.66|
Chromium is the 13th most abundant element in the Earth’s crust . Chromium is not present in free form. It is present in form of various ores, and the most common ore is iron chromium oxide FeCr 2 O4, which is termed as chromite. Chromite is the principal source of chromium that is used in pigments, worldwide. Chromium is released in the environment by erosion of rocks that contain chromium. Volcanic activities also play important role in the distribution of chromium. The largest producer of chromite is South Africa, followed by India, Brazil, Turkey, Finland and Kazakhstan . Russia has deposits of the rare native form of chromium in Udachnaya Pipe, from which native chromium and diamonds are extracted. The annual production of chromite is about 28.8 million metric tons, which is primarily being used in the production of steel.
Chromium is steel-gray in color. It is shiny, hard and brittle metal, that is easy to break. The density of chromium is 7.1 g.cm-3. Chromium has a highly polishable texture. It is resistant to tarnishing upon exposure with air. Chromium has outstanding magnetic properties. It is very dense metal and has a thermal conductivity of 93.9 W .
Chromium form variety of compounds and exists in many oxidation states, including +3, +6, +1. +4 and +5. The predominant and most stable oxidation state of chromium is +3 . Large number of chromium [III] compounds are present, such as compound of chromium with sulfuric and hydrochloric acid. Chromium (VI) compounds, including chromate anion (CrO42-), are powerful oxidizing agents.
Significance and Use
- The widest usage of chromium is in the making of metal alloys. Chromium can impart strength corrosion resistance and shine to various metals and is widely used in the manufacturing of steel.
- Chromium is widely used as coating agent, as it is highly durable and strong as compared to other metals. Chromium plating is used for bikes and cars.
- Chromium has been widely used in the manufacturing of dyes, pigments and paints due to its unique and wide range of colors.
- Chromium oxides are used for dying glass and ceramics. It imparts natural green color and is also used by armed forces to paint their tanks and vehicles to imitate infrared reflectance of green leaves and give them camouflage.
- Chromium is widely used for tanning of leather. Chromium has the ability to cross link the collagen fibers of leather and provide stability.
- Chromium is used in the making of blast furnace, kilns, brick mold and sand in foundry for casting of metals.
- Chromium compounds (with acids) are used for cleaning purposes due to their oxidizing properties.
Chromium has a significant role in the body of living organisms. In humans, chromium plays crucial role in the metabolism of sugar in the body. Chromium deficiency is also linked with diabetes by affecting the function of insulin (a hormone that plays important role in the metabolism of sugar, proteins and fat) . In contrast, Cr (VI) is highly toxic compound. It can lead to mutagenic effect and lung damaging effects if inhaled. If Cr (VI) is ingested in contaminated water, it can lead to various stomach complications, including tumors. The range of oral toxicity concentration is 50 to 150 mg/kg of Cr (VI). Skin contact with hexavalent chromium can aggravate allergic reaction termed as allergic contact dermatitis . Chromium can enter our body through food cooked in stainless steel pots. Chromium (III) is also considered toxic and have mutagenic effects on DNA . Large amounts of chromium compounds are being released into environment by various industries, tanneries (paints, dyes, leather manufacturing), and pose threat of contamination of soil and water.
Isotopes of Chromium
Natural chromium has four isotopes: chromium-50, chromium-52, chromium-53, chromium-54. There are twenty-one other isotopes of chromium. Chromium-53 is the most abundant among all isotopes. Several isotopes of chromium are used for medical purposes. For instance, chromium-51 is used for studying survival and growth of red blood cells and for measuring blood volume .
. Per Enghag, Encyclopedia of the elements: technical data, history, processing, applications.,p 577- 578, John Wiley and Sons, 2004
. Papp, John F. “Mineral Yearbook 2015: Chromium” (PDF). United States Geological Survey. Retrieved 2015-06-03.
. Clark, Jim. “Oxidation states (oxidation numbers)”. Chemguide. Retrieved 3 October 2018
 Chromium”. Office of Dietary Supplements, US National Institutes of Health. 2016. Retrieved 26 June 2016.
. Eastmond, David A.; MacGregor, J. T.; Slesinski, R. S. (2008). “Trivalent Chromium: Assessing the Genotoxic Risk of an Essential Trace Element and Widely Used Human and Animal Nutritional Supplement”. Critical Reviews in Toxicology. 38 (3): 173–190. doi:10.1080/10408440701845401. PMID 18324515.
. Naturally occurring isotope abundances: Commission on Atomic Weights and Isotopic Abundances report for the International Union of Pure and Applied Chemistry in Isotopic Compositions of the Elements 1989, Pure and Applied Chemistry, 1998, 70, 217. [Copyright 1998 IUPAC]