Periodic Table of the Elements
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Bottom FACULTY OF CHEMICAL TECHNOLOGY o PERIODIC TABLE OF THE ELEMENTS Bottom
  A B C D E F G H I J K L M N O P R S T U V X Z  
Periodic Table of the Elements Tableau périodique des éléments Periodni sustav elemenata Tavola periodica degli elementi Das Periodensystem der Elemente
Chromium Chrome Krom Cromo Chrom

 
Atomic number: 24
Group numbers: 6
Period: 4
 
Discovery date: 1797
Cr

Chromum
NEIGHBOURS

 
 
 
23
V
 24
Cr
 25
Mn
41
Nb
 42
Mo
 43
Tc


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Chromium was discovered by Louis-Nicholas Vauquelin (France) in 1797. The origin of the name comes from the Greek word chroma meaning colour. It is very hard, crystalline, steel-grey metal. The pure metal has a blue-white colour. It is hard, brittle and corrosion-resistant at normal temperatures. Hexavalent compounds toxic by skin contact.
Bottom TRANSITION ELEMENT: CHROMIUM GROUP Top

Relative atomic mass: 51.9961(6) Electronic configuration: [Ar] 3d5 4s1
Formal oxidation number: +2 +3 +6 Electronegativities: 1.66
Thermal conductivity: 93.7 W m-1 K-1 Electrical resistivity (20 °C): 12.9 μΩcm
Atomic radius: 124.9 pm Standard state (20 °C): solid
Density (g dm-3): 7190 (293 K)
6460 (m.p.)		 Molar volume (cm3 mol-1): 7.23 (293 K)
8.05 (m.p.)


Bottom THERMAL PROPERTIES Top

Melting point: 1907 °C Heat of fusion: 15.3 kJ mol-1
Boiling point: 2671 °C Heat of vaporization: 341.8 kJ mol-1
Critical temperature: 4427 °C Heat of atomization: 394.51 kJ mol-1


Bottom IONIZATION ENERGIES AND ABUNDANCE Top

1st ionization energy: 652.87 kJ mol-1 Abundance of element (air): - ppm
2nd ionization energy: 1590.64 kJ mol-1 Abundance of element (Earth's crust): 185 ppm
3rd ionization energy: 2987.21 kJ mol-1 Abundance of element (oceans): 0.00005 ppm


Bottom ISOTOPES Top

Isotopes Relative atomic mass Abundance (%)
50Cr49.946050(1)4.345(13)
52Cr51.940512(2)83.789(18)
53Cr52.940654(2)9.501(17)
54Cr53.938885(1)2.365(7)


Bottom MINERALS AND USES Top

The most important chromium mineral is chromite [Fe,Mg(CrO4)]. Produced commercially by heating its ore in the presence of silicon or aluminium. Used to make stainless steel. It gives the colour to rubies and emeralds. Iron-nickel-chromium alloys in various percentages yield an incredible variety of the most important metals in modern technology. The price of 99.98 % pure chromium shot is 744.80 € for 1000 g.

Bottom REDUCTION POTENTIALS Top

Balanced half-reaction   Eo / V      Annotation
Cr3+ + e- = Cr2+ - 0.408  
Cr3+ + 3e- = Cr(s) - 0.744  
Cr2+ + 2e- = Cr(s) - 0.91  
Cr2O72- + 14H+ + 6e- = 2Cr3+ + 7H2O +1.33  
Cr2O72- + 12H+ + 6e- = 2CrOH2+ + 5H2O +1.26  
Cr2O72- + 10H+ + 6e- = 2Cr(OH)2+ + 3H2O +1.14  
Cr2O72- + 14H+ + 12e- = 2Cr(s) + 7H2O +0.29  
HCrO4- + 7H+ + 3e- = Cr3+ + 4H2O +1.20  
CrO42- + 4H2O + 3e- = Cr(OH)3(s) + 5OH- - 0.13  
HCrO4- + 6H+ + 3e- = CrOH2+ + 3H2O +1.28  
CrO42- + 7H+ + 3e- = CrOH2+ + 3H2O +1.40  
CrO42- + 6H+ + 3e- = Cr(OH)2+ + 2H2O +1.28  
CrO42- + 4H+ + 3e- = CrO2- + 2H2O +0.95  
CrO42- + 2H+ + 3e- = CrO33- + H2O +0.36  

 

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