In infrared, at 425 μm, chromium has a maximum reflectance of about 72%, reducing to a minimum of 62% at 750 μm before rising again to 90% at 4000 μm. The electrical resistivity of chromium at 20 ☌ is 125 nanoohm- meters.Ĭhromium has a high specular reflection in comparison to other transition metals. The boiling point of 2671 ☌ (4840 ☏), however, is comparatively lower, having the fourth lowest boiling point out of the Period 4 transition metals alone behind copper, manganese and zinc. However, it still has the second highest melting point out of all the Period 4 elements, being topped by vanadium by 3 ☌ (5 ☏) at 1910 ☌ (3470 ☏). Chromium is highly resistant to tarnishing, which makes it useful as a metal that preserves its outermost layer from corroding, unlike other metals such as copper, magnesium, and aluminium.Ĭhromium has a melting point of 1907 ☌ (3465 ☏), which is relatively low compared to the majority of transition metals. Its Mohs hardness is 8.5, which means that it can scratch samples of quartz and topaz, but can be scratched by corundum. Bulk Sample of pure chromium metalĬhromium is extremely hard, and is the third hardest element behind carbon ( diamond) and boron. Chromium(VI) is a strong oxidising agent in contrast to the molybdenum(VI) and tungsten(VI) oxides.
#Chromium iii carbonate chemical formula series#
(Similar promotions happen for every transition metal atom but one, palladium.) Ĭhromium is the first element in the 3d series where the 3d electrons start to sink into the nucleus they thus contribute less to metallic bonding, and hence the melting and boiling points and the enthalpy of atomisation of chromium are lower than those of the preceding element vanadium. This lowers the energetic cost of promotion and increases the energy released by it, so that the promotion becomes energetically feasible and one or even two electrons are always promoted to the 4s subshell. However, in the 3d transition metals, the energy gap between the 3d and the next-higher 4s subshell is very small, and because the 3d subshell is more compact than the 4s subshell, inter-electron repulsion is smaller between 4s electrons than between 3d electrons. In the previous elements, the energetic cost of promoting an electron to the next higher energy level is too great to compensate for that released by lessening inter-electronic repulsion. This occurs because electrons in the same orbital repel each other due to their like charges. This occurs again later in the periodic table with other elements and their electron configurations, such as copper, niobium, and molybdenum. It is also the first element in the periodic table whose ground-state electron configuration violates the Aufbau principle. Physical properties Atomic Ĭhromium is the fourth transition metal found on the periodic table, and has an electron configuration of 3d 5 4s 1. Ībandoned chromium production sites often require environmental cleanup. According to the European Chemicals Agency (ECHA), chromium trioxide that is used in industrial electroplating processes is a "substance of very high concern" (SVHC). While chromium metal and Cr(III) ions are considered non-toxic, hexavalent chromium, Cr(VI), is toxic and carcinogenic. However, in 2014, the European Food Safety Authority, acting for the European Union, concluded that there was insufficient evidence for chromium to be recognized as essential. In the United States, trivalent chromium (Cr(III)) ion is considered an essential nutrient in humans for insulin, sugar, and lipid metabolism. Pure chromium metal is produced by a different process: roasting and leaching of chromite to separate it from iron, followed by reduction with carbon and then aluminium. Ferrochromium is then used to produce alloys such as stainless steel. Industrial production of chromium proceeds from chromite ore (mostly FeCr 2O 4) to produce ferrochromium, an iron-chromium alloy, by means of aluminothermic or silicothermic reactions. The name of the element is derived from the Greek word χρῶμα, chrōma, meaning color, because many chromium compounds are intensely colored. Polished chromium reflects almost 70% of the visible spectrum, and almost 90% of infrared light.
Chromium is also greatly valued as a metal that is able to be highly polished while resisting tarnishing. Stainless steel and chrome plating ( electroplating with chromium) together comprise 85% of the commercial use.
A major development in steel production was the discovery that steel could be made highly resistant to corrosion and discoloration by adding metallic chromium to form stainless steel. Ĭhromium metal is valued for its high corrosion resistance and hardness. It is a steely-grey, lustrous, hard, and brittle transition metal. Chromium is a chemical element with the symbol Cr and atomic number 24.
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