Chromium

Element	Chromium
Symbol	Cr
Atomic Number	24
Molar Mass	52 gmol^-1
Electron Configuration	[Ar]3d⁵4s¹
Normal State	solid metal
Density @STP	7.19 g cm^-3
Melting Point	1907^oC
Boiling Point	2671^oC
Stable Isotopes	⁵⁰Cr, ⁵²Cr, ⁵³Cr, ⁵⁴Cr
Atomic Radius	129 pm
Ionic Radius	84 (2+) pm
Electronegativity (Pauling)	1.66
Ionization Energy (1^st)	653 kJ mol^-1
Ionization Energy (2^nd)	1492 kJ mol^-1
Ionization Energy (3^rd)	2987 kJ mol^-1
Molar Heat Capacity	23.4 J K^-1mol^-1
Standard Molar Entropy	23.8 J K^-1mol^-1
Enthalpy of Fusion	15.3 kJ mol^-1
Enthalpy of Vapourization	348.78 kJ mol^-1

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Chromium is a hard silvery metallic transition metal element
Chromium discovered by Louis Nicolas Vauquelin (1794) and first isolation (1797)
Chromium is the only elemental solid showing antiferromagnetic ordering at and below room temperature, above 38 °C it changes to paramagnetic
Chromium is passivated by oxidation readily in air forming a thin, protective, surface layer leading to excellent anti-corrosion properties
Chromium is the 22nd most abundant element in Earth's crust
Although rare, deposits of native chromium exist
Chromium is mined as chromite (FeCr2O4) ore
Chromium has a wide range of oxidation states, with +3 the most stable, +3 and +6 are the most common, while +1, +4 and +5 are less common.
Metal alloys account for 85% of the use of chromium. The remainder is used in the chemical, refractory, and foundry industries
Pure chromium metal rarely used alone, except as an electoplated deposit (decorative or hard chrome plate)
Strengthening effect and increase in corrosion resistance made chromium an important alloying material for steel and other metal alloys
Chromium is an important alloying addition to stainless steel, nickel and cobalt super alloys and many other metal alloys
Strong oxidative properties of chromates are used to form protective oxide layer on metals like aluminium, zinc and cadmium (chromate conversion coating process)
Chromium compounds used in dye, pigments, leather tanning, primers, paints, wood preservatives
Chromium gives colour to rubies and saphire gem stones, synthetic ruby crystal was used for the first laser (1960) relying on emission of light from the chromium atoms
Chromium forms important refracory materials
Chromium(IV) oxide is used to manufacture magnetic tape used in high-performance audio tape and standard audio cassettes
Chromium(III) oxide (Cr2O3) is a metal polish known as green rouge
Chromium(III) oxide (Cr2O3) is thermal sprayed to produce extremely hard protective coatings on many substrates
Chrome alum is Chromium(III) potassium sulfate and is used as a mordant (a fixing agent) for dyes in fabric and in tanning
Trivalent chromium, Cr(III), or Cr3+ is an essential nutrient as a trace element
Hexalent chromium, Cr(VI), or Cr6+ is highly toxic and mutagenic

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