Difference between revisions of "Chromium"

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m (Wrong atomic number.)
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{{Infobox element
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<!-- General properties -->
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|name=Chromium
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|symbol=Cr
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|pronounce=
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|pronounce ref=
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|pronounce comment=
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|pronounce 2=
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|alt name=
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|alt names=
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|allotropes=
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|appearance=Silvery metallic
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<!-- Periodic table -->
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|above=
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|below=[[Molybdenum|Mo]]
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|left=[[Vanadium]]
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|right=[[Manganese]]
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|number=24
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|atomic mass=51.9961(6)
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|atomic mass 2=
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|atomic mass ref=
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|atomic mass comment=
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|series=
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|series ref=
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|series comment=
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|series color=
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|group=6
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|group ref=
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|group comment=
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|period=4
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|period ref=
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|period comment=
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|block=d
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|block ref=
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|block comment=
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|electron configuration=[Ar] 3d<sup>5</sup> 4s<sup>1</sup>
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|electron configuration ref=
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|electron configuration comment=
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|electrons per shell=2, 8, 13, 1
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|electrons per shell ref=
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|electrons per shell comment=
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<!-- Physical properties -->
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|physical properties comment=
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|color=Silvery metallic
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|phase=Solid
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|phase ref=
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|phase comment=
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|melting point K=2180
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|melting point C=1907
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|melting point F=​3465
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|melting point ref=
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|melting point comment=
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|boiling point K=2944
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|boiling point C=2671
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|boiling point F=​4840
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|boiling point comment=
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|sublimation point K=
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|sublimation point C=
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|sublimation point F=
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|sublimation point ref=
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|sublimation point comment=
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|density gplstp=
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|density gplstp ref=
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|density gplstp comment=
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|density gpcm3nrt=7.19
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|density gpcm3nrt 3=
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|density gpcm3mp=6.3
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|density gpcm3bp=
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|density gpcm3bp ref=
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|molar volume=
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|molar volume unit =
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|molar volume comment=
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|triple point K=
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|triple point kPa=
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|triple point ref=
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|triple point comment=
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|triple point K 2=
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|triple point kPa 2=
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|critical point K=
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|critical point MPa=
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|critical point comment=
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|heat fusion=21.0
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|heat fusion ref=
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|heat fusion comment=
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|heat fusion 2=
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|heat fusion 2 ref=
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|heat fusion 2 comment=
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|heat vaporization=347
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|heat vaporization ref=
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|heat vaporization comment=
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|heat capacity=23.35
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|heat capacity ref=
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|heat capacity comment=
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|heat capacity 2=
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|heat capacity 2 ref=
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|heat capacity 2 comment=
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|vapor pressure 1=1656
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|vapor pressure 10=1807
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|vapor pressure 100=1991
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|vapor pressure 1 k=2223
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|vapor pressure 10 k=2530
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|vapor pressure 100 k=2942
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|vapor pressure ref=
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|vapor pressure comment=
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|vapor pressure 1 2=
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|vapor pressure 10 2=
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|vapor pressure 100 2=
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|vapor pressure 1 k 2=
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|vapor pressure 10 k 2=
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|vapor pressure 2 ref=
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|vapor pressure 2 comment=
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<!-- Atomic properties -->
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|atomic properties comment=
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|oxidation states='''6''', 5, 4, '''3''', 2, 1, −1, −2, −4
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|oxidation states ref=
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|oxidation states comment=(depending on the oxidation state, an acidic, basic, or amphoteric oxide)
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|electronegativity=1.66
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|electronegativity ref=
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|electronegativity comment=
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|ionization energy 1=652.9
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|ionization energy 1 ref=
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|ionization energy 1 comment=
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|ionization energy 2=1590.6
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|ionization energy 2 ref=
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|ionization energy 2 comment=
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|ionization energy 3=2987
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|ionization energy 3 ref=
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|ionization energy 3 comment=
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|number of ionization energies=
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|ionization energy ref=
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|ionization energy comment=
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|atomic radius=128
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|atomic radius ref=
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|atomic radius comment=
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|atomic radius calculated=
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|atomic radius calculated ref=
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|atomic radius calculated comment=
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|covalent radius=139±5
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|covalent radius ref=
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|covalent radius comment=
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|Van der Waals radius=
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<!-- Miscellanea -->
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|crystal structure=
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|crystal structure prefix=
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|crystal structure ref=
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|crystal structure comment=Body-centered cubic (bcc)
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|crystal structure 2=
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|crystal structure 2 prefix=
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|crystal structure 2 ref=
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|crystal structure 2 comment=
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|speed of sound=
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|speed of sound ref=
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|speed of sound comment=
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|speed of sound rod at 20=5940
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|speed of sound rod at 20 ref=
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|speed of sound rod at 20 comment=
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|speed of sound rod at r.t.=
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|speed of sound rod at r.t. ref=
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|speed of sound rod at r.t. comment=
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|thermal expansion=
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|thermal expansion ref=
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|thermal expansion comment=
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|thermal expansion at 25=4.9
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|thermal expansion at 25 ref=
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|thermal expansion at 25 comment=
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|thermal conductivity=93.9
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|thermal conductivity ref=
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|thermal conductivity comment=
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|thermal conductivity 2=
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|electrical resistivity=
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|electrical resistivity comment=
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|electrical resistivity at 0=
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|electrical resistivity at 0 ref=
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|electrical resistivity at 0 comment=
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|electrical resistivity at 20=125·10<sup>-9</sup>
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|electrical resistivity at 20 ref=
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|electrical resistivity at 20 comment=
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|band gap=
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|band gap ref=
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|band gap comment=
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|Curie point K=
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|Curie point ref=
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|Curie point comment=
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|magnetic ordering=Antiferromagnetic
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|magnetic ordering ref=
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|magnetic ordering comment=
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|tensile strength=
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|tensile strength ref=
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|tensile strength comment=
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|Young's modulus=279
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|Young's modulus ref=
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|Young's modulus comment=
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|Shear modulus=115
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|Shear modulus ref=
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|Shear modulus comment=
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|Bulk modulus=160
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|Bulk modulus ref=
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|Bulk modulus comment=
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|Poisson ratio=0.21
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|Poisson ratio ref=
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|Poisson ratio comment=
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|Mohs hardness=8.5
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|Mohs hardness ref=
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|Mohs hardness comment=
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|Mohs hardness 2=
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|Mohs hardness 2 ref=
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|Mohs hardness 2 comment=
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|Vickers hardness=1060
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|Vickers hardness ref=
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|Vickers hardness comment=
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|Brinell hardness=687–6500
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|Brinell hardness ref=
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|Brinell hardness comment=
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|CAS number=7440-47-3
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|CAS number ref=
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|CAS number comment=
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<!-- History -->
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|naming=
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|predicted by=
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|discovered by=
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|discovery date=
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|first isolation by=
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|first isolation date ref=
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|first isolation date=
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|discovery and first isolation by=Louis Nicolas Vauquelin (1797-1798)
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|named by=
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|named date ref=
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|named date=
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|history comment label=
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|history comment=
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<!-- Isotopes -->
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|isotopes=
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|isotopes comment=
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|engvar=
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}}
 
'''Chromium''' is a transition metal with the symbol '''Cr''' and atomic number 24.
 
'''Chromium''' is a transition metal with the symbol '''Cr''' and atomic number 24.
  

Revision as of 21:28, 10 October 2017

Chromium,  24Cr
General properties
Name, symbol Chromium, Cr
Appearance Silvery metallic
Chromium in the periodic table

↑
Cr
↓
Mo
Vanadium ← Chromium → Manganese
Atomic number 24
Standard atomic weight (Ar) 51.9961(6)
Group, block , d-block
Period period 4
Electron configuration [Ar] 3d5 4s1
per shell
 2, 8, 13, 1
Physical properties
Silvery metallic
Phase Solid
Melting point 2180 K ​(1907 °C, ​​3465 °F)
Boiling point 2944 K ​(2671 °C, ​​4840 °F)
Density near r.t. 7.19 g/cm3
when liquid, at  6.3 g/cm3
Heat of fusion 21.0 kJ/mol
Heat of 347 kJ/mol
Molar heat capacity 23.35 J/(mol·K)
 pressure
Atomic properties
Oxidation states 6, 5, 4, 3, 2, 1, −1, −2, −4 ​(depending on the oxidation state, an acidic, basic, or amphoteric oxide)
Electronegativity Pauling scale: 1.66
energies 1st: 652.9 kJ/mol
2nd: 1590.6 kJ/mol
3rd: 2987 kJ/mol
Atomic radius empirical: 128 pm
Covalent radius 139±5 pm
Miscellanea
Crystal structure ​Body-centered cubic (bcc)
Speed of sound thin rod 5940 m/s (at 20 °C)
Thermal expansion 4.9 µm/(m·K) (at 25 °C)
Thermal conductivity 93.9 W/(m·K)
Electrical resistivity 125·10-9 Ω·m (at 20 °C)
Magnetic ordering Antiferromagnetic
Young's modulus 279 GPa
Shear modulus 115 GPa
Bulk modulus 160 GPa
Poisson ratio 0.21
Mohs hardness 8.5
Vickers hardness 1060 MPa
Brinell hardness 687–6500 MPa
CAS Registry Number 7440-47-3
Discovery and first isolation Louis Nicolas Vauquelin (1797-1798)
· references

Chromium is a transition metal with the symbol Cr and atomic number 24.

Properties

Chemical

Chromium metal is quite unreactive. It tends to form a thin passivation layer of chromium(III) oxide, which prevents further oxidation. Nitric acid can enhance this passivation layer, but reducing agents tend to destroy it.

Most chromium compounds are amphoteric.

Physical

Chromium is a shiny silver color and is quite hard and brittle. It is antiferromagnetic at room temperature, and is the only element that exhibits this property at such high temperatures. Chromium metal melts at 1907 °C and boils at 2671 °C. It has a density of 7.19 g/cm3

Availability

Pure chromium metal is hard to find, as it tends to be alloyed with different metals. Chromoly, which consists of iron, chromium and molybdenum, tends to have a relatively high concentration of chromium compared to other alloys. Stainless steel is another option.

Chromium makes up 10% or more of stainless steel, a very accessible metal to the home chemist. See Preparation for extraction of chromium from this.

Preparation

Aluminothermic reactions (thermites) with chromium(III) oxide may form chromium metal.

Chromium hydroxide can be produced from stainless steel by first dissolving the metal in hot hydrochloric acid. Iron can be precipitated out as iron(III) sulfate by reacting the resulting solution with sulfuric acid or sodium sulfate in a heated, oxidative environment. With the precipitate filtered out, chromium hydroxide can finally be precipitated from the solution using ammonia, sodium hydroxide, or sodium carbonate. An excess of ammonia or sodium hydroxide will dissolve the precipitate, again, so a nearly stoichiometric amount is recommended. The final product has some iron contamination as well.

Projects

Handling

Safety

Bulk chromium has good chemical resistivity and isn't known to cause contact dermatitis. Chromium(III) is known to be an essential trace element in the organism. Studies done so far have not shown whether Cr(III) poses any toxic or mutagenic preoperties, as the results are inconclusive.

Hexavalent chromium on the other hand is a known carcinogenic.

Storage

Bulk chromium does not require special storage, though it should be kept away from any halogens and mineral acid vapors.

Disposal

Chromium and Cr(III) pose little toxicity to the environment, though it's best to avoid dumping them in the environment.

Hexavalent chromium must be reduced to Cr(III) before disposal. This is done with a reducing agent, sulfites of metabisulfites should do the trick.

References

Relevant Sciencemadness threads

Retrieved from "https://www.sciencemadness.org/smwiki/index.php?title=Chromium&oldid=7755"