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CHROMIUM
Links:
Introduction Classification Description Physical Properties
Electron Configuration and Bonding Thermochemistry Video
Isotopes Reactions Abundance Compounds
Safety Languages For More Information Sources
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Introduction

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Atomic Number: 24 Group: 6 or VI B 24 51.9961
Average Atomic Mass: 51.9961 Period: 4

Cr
   

CAS Number:

 7440-47-3
      Chromium
Classification

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Metal Nonmetal Metalloid    
Alkali Metal Alkali Earth Metal Transition Metal Chalcogen Halogen
Noble Gas Lanthanoid Actinoid

Rare Earth Metal

  
Transuranium No Stable Isotopes      
Solid Liquid Gas

Assumed Solid

  
Description

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Discovered in 1797 by Vauquelin, who prepared the metal the next year, chromium is a steel-gray, lustrous, hard metal that takes a high polish. The principal ore is chromite (FeCr2O4), which is found in Zimbabwe, Russia, Transvaal, Turkey, Iran, Albania, Finland, Democratic Republic of Madagascar, and the Philippines. The metal is usually produced by reducing the oxide with aluminum. Chromium is used to harden steel, to manufacture stainless steel, and to form many useful alloys. Much is used in plating to produce a hard, beautiful surface and to prevent corrosion. Chromium is used to give glass an emerald green color. It finds wide use as a catalyst. All compounds of chromium are colored; the most important are the chromates of sodium and potassium (K2CrO4) and the dichromates (K2Cr2O7) and the potassium and ammonium chrome alums, as KCr(SO4)2 · 12H2O. The dichromates are used as oxidizing agents in quantitative analysis, also in tanning leather. Other compounds are of industrial value; lead chromate is chrome yellow, a valued pigment. Chromium compounds are used in the textile industry as mordants, and by the aircraft and other industries for anodizing aluminum. The refractory industry has found chromite useful for forming bricks and shapes, as it has a high melting point, moderate thermal expansion, and stability of crystalline structure. Many chromium compounds are toxic and should be handled with proper safeguards. Natural chromium contains four isotopes. Sixteen other isotopes are known. Chromium metal (99.99%) costs about $200/kg. Commercial grade chromium (99%) costs about $75/kg. 1
Physical Properties

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Normal Melting Point: 1907 °C = 2180.15 K = 3464.6 °F 2 Normal Boiling Point: 2671 °C = 2944.15 K = 4839.8 °F 2
Sublimation Point: Triple Point:
Critical Point:
Density: 7.19 g/cm3 Crystal Structure: cubic: body centered
Atomic Radius: 1.85 Ǻ = 185 pm Covalent Radius: 1.18 Ǻ = 118 pm
Ionic Radius: 1 Ǻ = 100 pm Atomic Volume: 7.23 cm3/mol
Qualitative Solubility: i; s dil HCl, H2SO4 3
Note: Unless otherwise stated, solubility is for water at 25 degrees Celsius.
Electron Configuration and Bonding

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Predicted Electron Configuration: [Ar] 4s2 3d4

Lewis Dot Diagram
Actual Electron Configuration: [Ar] 4s1 3d5  

x

 
Block: d

Cr

Highest Occupied Energy Level: 4

Valence Electrons: 1  

 
Quantum Numbers: n = 3 ℓ = 2 mℓ = 2 ms = +½        
Please note that information in this section can be derived entirely from the periodic table.  Although most people do not discuss valence electrons of the d-block and f-block elements, on this page the number of electrons in the highest energy level of the actual electron configuration was used to determine valence electrons.
Electronegativity (Pauling): 1.66 Electropositivity (Pauling): 2.34
Electron Affinity: 0.67 eV = 64.65 kJ/mol = 15.45 kcal/mol Oxidation States: +3,2,6
Work Function:4 4.40 eV = 7.0488E-19 J  
Ionization Potential 5 eV kJ/mol Ionization Potential 5 eV kJ/mol
1 6.7665 652.9 13 354.8 34233.0
2 16.4857 1590.6 14 384.168 37066.6
3 30.96 2987.2 15 1010.6 97508.1
4 49.16 4743.2 16 1097 105844.4
5 69.46 6701.9 17 1185 114335.1
6 90.6349 8744.9 18 1299 125334.4
7 160.18 15455.0 19 1396 134693.5
8 184.7 17820.8 20 1496 144342.0
9 209.3 20194.4 21 1634 157657.0
10 244.4 23581.0 22 1721.4 166089.8
11 270.8 26128.2 23 7481.7 721874.1
12 298 28752.6 24 7894.81 761733.2
Note: Only the electronvolt values are given in the CRC Handbook, a conversion factor was used to find the kJ/mol value.
Thermochemistry

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Specific Heat: 0.45 J/g°C = 0.108 cal/g°C Thermal Conductivity: 93.7 (W/m)/K, 27ºC
Heat of Fusion: 16.9 kJ/mol = 325.0 J/g Heat of Vaporization: 344.3 kJ/mol = 6621.7 J/g
State of Matter Enthalpy of Formation Entropy of Formation Gibbs Free Energy
(kcal/mol) (kJ/mol) (cal/K) (J/K) (kcal/mol) (kJ/mol)
(s) 0 0 5.645 23.61868 0 0
(l) 6.239 26.103976 8.660 36.23344 5.340 22.34256
(g) 95.00 397.48 41.64 174.22176 84.27 352.58568
Video

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Video on chromium from the University of Nottingham's periodicvideos.com
A solution of chromium(III) ions is reacted with sodium hydroxide. Initially, a precipitate is formed, but excess amounts of sodium hydroxide yield green hexahydroxochromate(III) ions. When hydrogen peroxide is added in the presence of heat, the distinctive yellow color of the chromate ion can be seen. After cooling, the addition of concentrated sulfuric acid further oxidizes the chromium, yielding orange dichromate ions.
Isotopes

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Nuclide Mass Half-Life Nuclear Spin Binding Energy (kJ/mol)
42Cr 42.00643(32)# 14(3) ms [13(+4-2) ms] 0+ 29597935793.7866
43Cr 42.99771(24)# 21.6(7) ms (3/2+) 31186277873.8724
44Cr 43.98555(5)# 54(4) ms [53(+4-3) ms] 0+ 33044263665.5654
45Cr 44.97964(54) 50(6) ms 7/2-# 34362962034.0448
46Cr 45.968359(21) 0.26(6) s 0+ 36131066588.5358
47Cr 46.962900(15) 500(15) ms 3/2- 37449764957.0157
48Cr 47.954032(8) 21.56(3) h 0+ 38948225799.9003
49Cr 48.9513357(26) 42.3(1) min 5/2- 39997280456.7737
50Cr 49.9460442(11) STABLE 0+ 41226097588.0511
51Cr 50.9447674(11) 27.7025(24) d 7/2- 42185271007.7227
52Cr 51.9405075(8) STABLE 0+ 43324206901.7993
53Cr 52.9406494(8) STABLE 3/2- 44103617847.0663
54Cr 53.9388804(8) STABLE 0+ 45062791266.7372
55Cr 54.9408397(8) 3.497(3) min 3/2- 45662439737.6009
56Cr 55.9406531(20) 5.94(10) min 0+ 46441850682.8679
57Cr 56.943613(2) 21.1(10) s (3/2-) 46951617916.5284
58Cr 57.94435(22) 7.0(3) s 0+ 47641147624.5934
59Cr 58.94859(26) 460(50) ms 5/2-# 48061033621.0519
60Cr 59.95008(23) 560(60) ms 0+ 48660682091.915
61Cr 60.95472(27) 261(15) ms 5/2-# 49080568088.3735
62Cr 61.95661(36) 199(9) ms 0+ 49680216559.2354
63Cr 62.96186(32)# 129(2) ms (1/2-)# 50010221318.4932
64Cr 63.96441(43)# 43(1) ms 0+ 50519988552.1537
65Cr 64.97016(54)# 27(3) ms (1/2-)# 50760112074.2083
66Cr 65.97338(64)# 10(6) ms 0+ 51269879307.87
67Cr 66.97955(75)# 10# ms [>300 ns] 1/2-# 51510002829.9221
Values marked # are not purely derived from experimental data, but at least partly from systematic trends. Spins with weak assignment arguments are enclosed in parentheses. 6
Reactions

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Abundance

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Earth: Source Compounds: oxides 7
Earth: Ocean Water: 0.0003 mg/L 8
Earth: Crust: 102 mg/kg = 0.0102% 8
Earth: Lithosphere: 0.012% 9
Earth: Total: 4120 ppm 10
Mercury: Total: 7180 ppm 10
Venus: Total: 4060 ppm 10
Human Body: Total: 0.000003% 11
Compounds

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chromium trioxide chromium(III) fluoride chromium(III) sulfide
chromium(II) bromide chromium(III) iodide chromium(III) telluride
chromium(II) carbide chromium(III) nitrate chromium(IV) bromide
chromium(II) chloride chromium(III) nitrate nonahydrate chromium(IV) chloride
chromium(II) fluoride chromium(III) nitride chromium(IV) fluoride
chromium(II) iodide chromium(III) oxide chromium(IV) iodide
chromium(II) selenide chromium(III) phosphate chromium(IV) oxide
chromium(II, III) oxide chromium(III) picolinate chromium(V) fluoride
chromium(III) bromide chromium(III) potassium sulfate chromium(VI) carbonyl
chromium(III) chloride chromium(III) potassium sulfate dodecahydrate chromium(VI) fluoride
chromium(III) chloride hexahydrate chromium(III) sulfate chromium(VI) hydroxide
chromium(III) chromate chromium(III) sulfate hexahydrate chromium(VI) oxide
Safety

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Note: Not every link below has an entry for every element on the periodic table.  Sites were selected based on those that had a large number of element and compound entries.
Scorecard's Pollution Information − not an MSDS, but it does provide basic information (among other things) on human heath hazards and industrial uses.
Although not truly an MSDS, Oxford University's Physical and Theoretical Chemistry Laboratory does provide some basic information.
Iowa State University
ESPI Metals
Languages

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Afrikaans: Chroom Albanian: Krom Armenian: Քրոմ Arabic: كروم
Aromanian: Cromu Basque: Kromoa Bosnian: Hrom Breton: Krom
Bulgarian: Хром Byelorussian: Хром Catalan: Crom Chinese: 铬
Cornish: Cromyum Croatian: Krom Czech: Chrom (Barvík †) Danish: Chrom or Krom
Dutch: Chroom Esperanto: Kromo Estonian: Kroom Faroese: Krom
Finnish: Kromi French: Chrome Friulian: Crom Frisian: Groom
Galician: Cromo Georgian: ქრომი German: Chrom Greek: Χρωμιο
Hebrew: כרום Hungarian: Króm Icelandic: Króm Irish Gaelic: Cróimiam
Italian: Cromo Japanese: クロム Kashubian: Chróm Kazakh: Хром
Korean: 크롬, 크로뮴 Latvian: Hroms Lithuanian: Chromas Luxembourgish: Chrom
Macedonian: Хром Malay: Kromium, Krom Maltese: Kromjum Manx Gaelic: Cromium
Mokshan: Крома Mongolian: Хром Norwegian: Krom Occitan: Crom
Ossetian: Хром Polish: Chrom Portuguese: Crómo Russian: Хром
Scottish Gaelic: Cròimiam Serbian: Хром Slovak: Chróm Spanish: Cromo
Sudovian: Chramas Swahili: Kromi Swedish: Krom Tajik: Hrom
Thai: โครเมียม Turkish: Krom Ukranian: Хром Uzbek: Хром
Vietnamese: Crom Welsh: Cromiwm        
For More Information

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From Online Periodic Tables:
About.com American Elements
Chemical & Engineering News Chemical Elements
ChemGlobe Chemicool
Environmental Chemistry Eni Generalic
HyperPhysics from Georgia State University's Department of Physics and Astronomy InfoPlease
Lenntech Los Alamos National Laboratory
Physics Department of the University of Coimbra Qivx Inc.
Royal Society of Chemistry's Visual Elements Schenectady County Community College
Thomas Jefferson Lab National Accelerator Facility WebElements
Wikipedia X-ray properties: Carlo Segre from Illinois Institute of Technology
Sources

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(1) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 4-9.
(2) - Lide, David R. CRC Handbook; CRC Press: Boca Raton, FL, 2002; p 4-132.
(3) - Dean, John A. Lange's Handbook of Chemistry, 11th ed.; McGraw-Hill Book Company: New York, NY, 1973; p 4-8 - 4-149.
(4) - Speight, James. Lange's Handbook of Chemistry, 16th ed.; McGraw-Hill Professional: Boston, MA, 2004; p 1-132.
(5) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 10-178 - 10-180.
(6) - Atomic Mass Data Center. http://amdc.in2p3.fr/web/nubase_en.html (accessed July 14, 2009).
(7) - Silberberg, Martin S. Chemistry: The Molecular Nature of Matter and Change, 4th ed.; McGraw-Hill Higher Education: Boston, MA, 2006, p 965.
(8) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 14-17.
(9) - Silberberg, Martin S. Chemistry: The Molecular Nature of Matter and Change, 4th ed.; McGraw-Hill Higher Education: Boston, MA, 2006, p 962.
(10) - Silberberg, Martin S. Chemistry: The Molecular Nature of Matter and Change, 4th ed.; McGraw-Hill Higher Education: Boston, MA, 2006, p 964.
(11) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 7-17.

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Last update: Thursday, August 12, 2010