{"id":86,"date":"2020-04-08T15:02:40","date_gmt":"2020-04-08T15:02:40","guid":{"rendered":"https:\/\/thechemicalelements.com\/?page_id=86"},"modified":"2023-08-16T09:54:12","modified_gmt":"2023-08-16T09:54:12","slug":"chromium","status":"publish","type":"post","link":"https:\/\/thechemicalelements.com\/chromium\/","title":{"rendered":"Chromium (Cr)"},"content":{"rendered":"\n

Chromium is a chemical element with an atomic number of 24 in the periodic table of elements<\/a>. It\u2019s one of the most abundant naturally occurring elements in Earth\u2019s crust. This element, also known as the hardest metal on Earth, is a member of the transition metals family of periodic table elements and has six valence electron configuration that participates in numerous chemical bonds with the other chemical elements.<\/span><\/p>\n\n\n\n

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Chemical and Physical Properties of Chromium<\/span><\/h3>\n\n\n\n
Property<\/strong><\/td>Value<\/strong><\/td><\/tr>
The symbol in the periodic table of elements<\/td>Cr<\/td><\/tr>
Atomic number<\/td>24<\/td><\/tr>
Atomic weight (mass)<\/td>51.996 g.mol -1<\/td><\/tr>
Group number<\/td>6 (Transition metals)<\/td><\/tr>
Period<\/td>4<\/td><\/tr>
Color<\/td>A lustrous silvery-gray metal with a bluish hue<\/td><\/tr>
Physical state<\/td>Solid at room temperature<\/td><\/tr>
Half-life<\/td>27.8 days<\/td><\/tr>
Electronegativity according to Pauling<\/td>1.6<\/td><\/tr>
Density<\/td>7.19 g.cm-3 at 20\u00b0C<\/td><\/tr>
Melting point<\/td>1907 \u00b0C<\/td><\/tr>
Boiling point<\/td>2672 \u00b0C<\/td><\/tr>
Van der Waals radius<\/td>0.127 nm<\/td><\/tr>
Ionic radius<\/td>N\/A<\/td><\/tr>
Isotopes<\/td>6<\/td><\/tr>
Most characteristic isotope<\/td>52Cr, 53Cr, and 54Cr<\/td><\/tr>
Electronic shell<\/td>[Ar] 3d5 4s1<\/td><\/tr>
The energy of the first ionization<\/td>651.1 kJ.mol-1<\/td><\/tr>
The energy of the second ionization<\/td>1590.1 kJ.mol-1<\/td><\/tr>
Discovery date<\/td>In 1797 by N. L. Vauquelin<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

Chromium is a transition metal assigned with the periodic table symbol Cr, atomic number 24, has an atomic mass of 51.996 g.mol<\/span>-1<\/span>, and electron configuration [Ar] 3d<\/span>5<\/span> 4s<\/span>1<\/span>. It reaches its boiling point at 2672 \u00b0C, while the melting point is achieved at 1907 \u00b0C. <\/span><\/p>\n\n\n\n

This lustrous, brittle, and corrosion-resistant hard metal can be polished to a highly reflective surface. Apart from being resistant to heat, wear, and corrosion, chromium is also classified as a refractory metal, along with the elements molybdenum <\/a>(Mo) and tungsten (W). After the elements carbon <\/a>and boron<\/a>, chromium is the third hardest chemical element in the periodic table. Also, it\u2019s the only element that does not display any magnetic properties in its solid form. <\/span><\/p>\n\n\n\n

Highly reactive with the other chemical elements, chromium displays an electronegativity of 1.6 according to Pauling, whereas its atomic radius according to van der Waals is 0.127 nm. When exposed to high temperatures, the pure elemental form of chromium burns and forms the green chromium oxide compound.\u00a0<\/span><\/p>\n\n\n\n

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Passivation of Chromium Metal<\/span><\/h3>\n\n\n\n

When the metal form of chromium comes into contact with air, the oxygen <\/a>forms a thin layer of chromium oxide on the metal\u2019s surface. This so-called <\/span>passivation<\/span><\/i>, i.e. lack of chemical reactivity, protects chromium against corrosion. The German-Swiss chemist Christian Friedrich Sch\u00f6nbein (1799-1868) is the inventor of this passivation effect. <\/span><\/p>\n\n\n\n

Nowadays, passivation is widely used with stainless steel to protect the reaction of the metal with oxygen. It acts as an anti-corrosive barrier, prolongs the use of the metal products treated with this chemical procedure, and reduces the maintenance requirements of these products.\u00a0<\/span><\/p>\n\n\n\n

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How Does Passivation Work?<\/span><\/h4>\n\n\n\n

The combination of chromium, iron<\/a>, and nickel <\/a>as primary elements results in the production of stainless steel. Also, molybdenum, silicon<\/a>, manganese<\/a>, aluminum, and carbon may be added to this alloy. The strong anti-corrosive properties of chromium come forth when this chemical element is exposed to oxygen molecules as a part of the stainless steel alloy. <\/span><\/p>\n\n\n\n

The passivation process starts by applying acid to the stainless steel compound in order to remove the free iron molecules from the alloy\u2019s surface, while chromium remains unaffected. After the acid exposure, the alloy is exposed to oxygen in order to trigger the formation of the protective anti-corrosive barrier. When there are no free iron molecules on the surface of the alloy, there is no corrosive reaction because the thin chromium oxide film, formed upon contact of Cr with O<\/span>2<\/span>, protects the other metal components of the stainless steel alloy from corrosion. <\/span><\/p>\n\n\n\n

The process of passivation additionally reinforces the anti-corrosive property of the chromium since the formation of a chemically non-reactive surface on the alloy protects the stainless steel against rust.\u00a0<\/span><\/p>\n\n\n\n

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How Was Chromium Discovered?<\/span><\/h2>\n\n\n\n

Before discovering beryllium <\/a>in 1798, French chemist Nicolas Louis Vauquelin (1763 – 1829) had conducted multiple other chemical trials that resulted in new scientific discoveries. It was 1780 when Vauquelin\u2019s interest was piqued by a mineral sample of lead <\/a>chromate (also known as crocoite) taken from the mines in the Ural Mountains, Siberia. <\/span><\/p>\n\n\n\n

By attempting to prove that the mineral is not a lead ore as it was believed, the French chemist went on to boil the crushed mineral with potassium <\/a>carbonate. The reaction triggered by this experimental attempt further increased his genuine belief that he was on the brink of a new discovery. <\/span><\/p>\n\n\n\n

Namely, by conducting more and more experiments, Vauquelin tried to confirm his findings and prove that his work had produced a new chemical element. Finally, in 1781, the scientist succeeded in isolating the pure elemental form of chromium. First, he managed to remove lead from the mineral by exposing it to hydrochloric acid vapor. <\/span><\/p>\n\n\n\n

The evaporation produced by the reaction gave Vauquelin the oxide which he heated in a charcoal oven, and – the result was monumental! In this way, the French chemist confirmed his 1798 findings and proved the existence of a new chemical element – chromium. <\/span><\/p>\n\n\n\n

After the isolation of the pure chromium, Vauqelin also recognized traces of this element in the red and green precious stones – ruby and emerald.\u00a0<\/span><\/p>\n\n\n\n

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The Story About the Origin of New York\u2019s \u201cYellow Cab\u201d<\/span><\/h3>\n\n\n\n

Nowadays, chrome yellow is one of the most popular colors. It\u2019s become the most recognizable trademark of the school buses and cabs in the United States. The story about the popularization of the chromium yellow color begins in 1822. <\/span><\/p>\n\n\n\n

In this year, the German chemist Andreas Kurtz (1782 – 1846), who was also Vauquelin\u2019s student, attempted to produce larger quantities of potassium dichromate(VI), its chemical formula being K<\/span>2<\/span>Cr<\/span>2<\/span>O<\/span>7<\/span>. This inorganic chemical reagent with a bright, red-orange color, attracted the attention of the local manufacturers employed in the textile industry, so Kurtz started making profits out of the sales. <\/span><\/p>\n\n\n\n

However, the competition made this business unprofitable very soon, but this didn\u2019t discourage Vauquelin\u2019s student. Motivated by his first commercial success, Kurtz began producing other chrome pigments. Among them, his \u2018chrome yellow\u2019 pigment got in the newspaper headlines when the British princess Charlotte painted all her carriages in vivid yellow paint, made from lead(II) chromate – the yellow form of chromium. <\/span><\/p>\n\n\n\n

Throughout the times, the yellow color of the Princess\u2019s carriage remained a characteristic feature of public transport. Thus, today the school busses in the U.S. and especially the iconic cabs of New York are all colored in \u2018chromium yellow\u2019, reminiscent of the princess\u2019s practice and Kurtz\u2019s achievement.\u00a0<\/span><\/p>\n\n\n\n

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The Story About the Chrome King of the World <\/span><\/h3>\n\n\n\n

In the 1820s, Isaac Tyson, Jr. (1792\u20131861) was considered to be the biggest chromium magnate and successful industrialists. His story of success had begun in France, where he studied chemistry and mineralogy. This educational experience later proved to be his greatest asset. <\/span><\/p>\n\n\n\n

Upon his return to his hometown of Baltimore, Maryland, U.S., Tyson began to exploit the chromite accumulations on his farm. One day, he had noticed an unusual piece of mineral supporting a barrel at the local market. The knowledge he gained in chemistry school helped him make a logical connection between chromite and serpentine barrens rich in metal ores. Tyson recognized the serpentine mineral as the rare green rock that is used in the \u2018chrome yellow’ pigment production. <\/span><\/p>\n\n\n\n

This acknowledgment spurred him to invest in all available serpentine barrens in the United States, assuming that there are large deposits of chromite in the surrounding areas. In a blink, he had bought all the major chromite mining sites in Maryland, Pennsylvania, and Virginia. Before too long, he held a monopoly over the largest chromite deposits in the world. <\/span><\/p>\n\n\n\n

Following his business instincts, this American chemist and magnate commenced the production of chromium pigments in Philadelphia, United States, and the manufacture of dyes in Liverpool, England. By branching out his production, Tyson earned the title of \u201cthe Chrome King of The World\u201d! <\/span><\/p>\n\n\n\n

In 1996, this pioneer of the American chrome industry was inducted in the National Mining Hall of Fame in Leadville, Colorado, as a result of his successful initiatives and entrepreneurship.<\/span><\/p>\n\n\n\n

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How Did Chromium Get Its Name?<\/span><\/h2>\n\n\n\n

Because most chromium compounds always produce beautiful and vivid colors, this chemical element was labeled with the Greek word \u2018\u03c7\u03c1\u1ff6\u03bc\u03b1\u2019, i.e chr\u014dma, meaning \u2018color\u2019.<\/span><\/p>\n\n\n\n

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Where Can You Find Chromium?<\/span><\/h2>\n\n\n\n

Rarely found in its free elemental form, chromium is one of the most widely distributed chemical elements in Earth’s crust that can be found as a part of the massive ultramafic and serpentine rocks, volcanic eruptions, some plants, animals, gasses, and in soil. Uvarovite, volkonskoite, k\u00e4mmererite, and fuchsite are minerals also containing traces of chromium.<\/span><\/p>\n\n\n\n

Chromite (FeCr<\/span>2<\/span>O<\/span>4<\/span>) is the most frequent form of ore mined for chromium production. Chromium(0), chromium(III) oxide, and chromium(VI) are right behind chromite as the most frequently occurring forms of chromium in nature. South Africa, India, Kazakhstan, and Zimbabwe are the locations where the largest accumulations of chromite ore are found. <\/span><\/p>\n\n\n\n

The commercial form of chromium is obtained by oxidation of chromite ore to chromium(III) oxide (Cr2O3). After this process, the oxide is exposed to a high temperature in the presence of aluminum, carbon, or silicon. This reaction produces the pure form of chromium.<\/span><\/p>\n\n\n\n

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Chromium in Everyday Life<\/span><\/h2>\n\n\n\n

Due to its properties, chromium is widely used in many industries. It has a wide application in metallurgy, medicine, the chemical industry, the car industry, transport, the military, as well as in our everyday life:<\/span><\/p>\n\n\n\n