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Key People:Nicolas-Louis Vauquelin...(Show more)Related Topics:Chemical elementtransition metalChromium processing...(Show more)

Chromium (Cr), chemical element of team 6 (VIb) of the regular table, a difficult steel-gray steel that take away a high polish and is supplied in alloys to rise strength and corrosion resistance. Chromium was discovered (1797) through the French chemist Nicolas-Louis Vauquelin and isolated as the steel a year later; the was named for the multicoloured compounds. The eco-friendly colour the emerald, serpentine, and also chrome mica and the red color of ruby space due to little amounts that chromium. The name of the aspect chromium (from Greek chrōmos, “colour”) connotes the pronounced and also varied colorations the chromium compounds.


Element Propertiesatomic numberatomic weightmelting pointboiling pointspecific gravityoxidation stateselectron configuration
24
51.9961
1,890 °C (3,434 °F)
2,482 °C (4,500 °F)
7.20 (28 °C)
+2, +3, +6
3d54s1

Occurrence, uses, and properties

Chromium is a fairly abundant facet in earth crust; the free metal is never uncovered in nature. Many ores consist of the mineral chromite, the best formula of i beg your pardon is FeCr2O4. That is widely spread in herbal deposits, which room usually contaminated v oxygen, magnesium, aluminum, and also silica; your chromium contents varies native 42 come 56 percent. Among the chief provides of chromium is in ferrous alloys, because that which the pure steel is not required. Accordingly, chromite is often reduced with carbon in a furnace, creating the alloy ferrochromium, which consists of iron and chromium in an atom proportion of roughly 1 come 2.


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To acquire pure chromium, chromite is first treated v molten alkali and oxygen, converting all of the chromium to the alkali chromate, and also the last is liquified in water and eventually precipitated as salt dichromate, Na2Cr2O7. The dichromate is then reduced with carbon come chromium sesquioxide, Cr2O3, and also that oxide in turn is lessened with aluminum to give the chromium metal.

Chromium is included to iron and also nickel in the type of ferrochromium to develop alloys specially defined by their high resistance to corrosion and oxidation. Offered in tiny amounts, chromium hardens steel. Stainless steels space alloys the chromium and iron in i beg your pardon the chromium contents varies from 10 come 26 percent. Chromium alloys are supplied to fabricate such products as oil tubing, auto trim, and also cutlery. Chromite is offered as a refractory and also as a raw product for the production of chromium chemicals.


The metal is white, hard, lustrous, and brittle and is incredibly resistant to simple corrosive reagents; this resistance accounts for its considerable use together an electroplated safety coating. At elevated temperature chromium unites directly with the halogens or through sulfur, silicon, boron, nitrogen, carbon, or oxygen. (For additional treatment of chromium metal and also its production, see chromium processing.)

Natural chromium consists of a mixture of four stable isotopes: chromium-52 (83.76 percent), chromium-53 (9.55 percent), chromium-50 (4.31 percent), and chromium-54 (2.38 percent). The steel is paramagnetic (weakly attracted to a magnet). It exists in two forms: body-centred cubic (alpha) and hexagonal close-packed (beta). In ~ room temperature, chromium slowly dissolves in hydrochloric and dilute sulfuric acids. Certain oxidizing agents create a thin unreactive oxide class on the metal, rendering it passive also to dilute mineral acids, such together sulfuric, nitric, or cold aqua regia. At simple temperatures the steel shows no reaction come seawater or to wet or dry air.

Top producer of chromium include South Africa, India, Kazakhstan, and also Turkey.

Principal compounds

The most common oxidation claims of chromium room +6, +3, and +2. A few stable compound of the +5, +4, and +1 states, however, room known.

In the +6 oxidation state, the most important varieties formed by chromium are the chromate, CrO42−, and also dichromate, Cr2O72−, ions. These ions form the basis for a collection of industrially necessary salts. Amongst them are sodium chromate, Na2CrO4, and also sodium dichromate, Na2Cr2O7, which are supplied in animal leather tanning, in steel surface treatment, and also as catalysts in various commercial processes.

Chromium creates several commercially an useful oxygen compounds, the most important of which is chromium oxide, generally called chromium trioxide or chromic acid, CrO3, in i m sorry chromium is in the +6 oxidation state. One orange-red crystalline solid, chromic mountain liquefies gradually when exposed come moist air. That is usually created by therapy of sodium dichromate with sulfuric acid. Chromic acid is provided chiefly because that chromium plating however is additionally employed together a colorant in ceramics. That is a powerful oxidant and may react violently through some essential materials, yet such remedies are frequently utilized by managed oxidations in organic synthesis.

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Another far-ranging oxygen link is chromium oxide, additionally known as chromium sesquioxide or chromic oxide, Cr2O3, in i m sorry chromium is in the +3 oxidation state. It is prepared by calcining salt dichromate in the visibility of carbon or sulfur. Chromium oxide is a environment-friendly powder and also is employed extensively as a pigment; the hydrate form, well-known as Guignet’s green, is provided when chemical and heat resistance room required.