General
States
Energies
Oxidation & Electrons
Appearance & Characteristics
Reactions & Compounds
Radius
Conductivity
Abundance & Isotopes
States
Energies
Oxidation & Electrons
Appearance & Characteristics
Reactions & Compounds
Radius
Conductivity
Abundance & Isotopes
|
24
Cr
51.996
Chromium |
Chromium (Photo by Tomihahndorf)
General:
Name: Chromium
Type: Transition Metal
Density @ 293 K: 7.19 g/cm3
Discovery of Chromium
Chromium was discovered in 1780 by Nicolas-Louis Vanquelin. He discovered the element in a mineral sample of 'Siberian red lead'- now known as crocoite (lead chromate). He boiled the crushed mineral with potassium carbonate to produce lead carbonate and a yellow potassium salt solution of chromic acid. Vanquelin was convinced by further experiments on the solution that he had found a new metal.
In 1781 he succeeded in isolating the metal. Initially he removed the lead from the mineral sample by precipitation with hydrochloric acid. Vanquelin then obtained the oxide by evaporation and finally isolated chromium by heating the oxide in a charcoal oven(1)(2).
Vanquelin also identified small amounts of chromium in ruby and emerald stones.
Beryllium was also discovered by Louis-Nicholas Vauquelin in 1798.
Chromium was named from the Greek word 'chroma', meaning color because it forms a variety of colorful compounds.
Type: Transition Metal
Density @ 293 K: 7.19 g/cm3
Discovery of Chromium
Chromium was discovered in 1780 by Nicolas-Louis Vanquelin. He discovered the element in a mineral sample of 'Siberian red lead'- now known as crocoite (lead chromate). He boiled the crushed mineral with potassium carbonate to produce lead carbonate and a yellow potassium salt solution of chromic acid. Vanquelin was convinced by further experiments on the solution that he had found a new metal.
In 1781 he succeeded in isolating the metal. Initially he removed the lead from the mineral sample by precipitation with hydrochloric acid. Vanquelin then obtained the oxide by evaporation and finally isolated chromium by heating the oxide in a charcoal oven(1)(2).
Vanquelin also identified small amounts of chromium in ruby and emerald stones.
Beryllium was also discovered by Louis-Nicholas Vauquelin in 1798.
Chromium was named from the Greek word 'chroma', meaning color because it forms a variety of colorful compounds.
Symbol: Cr
Atomic weight: 51.996
Atomic volume: 7.23 cm3/mol
Atomic weight: 51.996
Atomic volume: 7.23 cm3/mol
States
State (s, l, g): solid
Melting point: 2180 K (1907 oC)
Melting point: 2180 K (1907 oC)
Boiling point: 2943 K (2670 oC)
Energies
Specific heat capacity: 0.45 J g-1 K-1
Heat of fusion: 21.0 kJ mol-1
1st ionization energy: 652.8 kJ mol-1
3rd ionization energy: 2987.2 kJ mol-1
Heat of fusion: 21.0 kJ mol-1
1st ionization energy: 652.8 kJ mol-1
3rd ionization energy: 2987.2 kJ mol-1
Heat of atomization: 397 kJ mol-1
Heat of vaporization: 339.5 kJ mol-1
2nd ionization energy: 1592 kJ mol-1
Electron affinity: 64.3 kJ mol-1
Heat of vaporization: 339.5 kJ mol-1
2nd ionization energy: 1592 kJ mol-1
Electron affinity: 64.3 kJ mol-1
Oxidation & Electrons
Shells: 2,8,13,1
Minimum oxidation number: -2
Min. common oxidation no.: 0
Electronegativity (Pauling Scale): 1.66
Minimum oxidation number: -2
Min. common oxidation no.: 0
Electronegativity (Pauling Scale): 1.66
Electron configuration: [Ar] 3d5 4s1
Maximum oxidation number: 6
Max. common oxidation no.: 3
Polarizability volume: 11.6 Å3
Maximum oxidation number: 6
Max. common oxidation no.: 3
Polarizability volume: 11.6 Å3
Appearance & Characteristics
Structure: bcc: body-centered cubic
Hardness: 8.5 mohs
Hardness: 8.5 mohs
Transition metals are well-known for their multiple colored ions. Here's an entertaining color change from Cr +6 (orange) to Cr +3 (green). Ammonium dichromate burns and forms chromium (III) oxide.
Color: silver-gray
Harmful effects:
Chromium metal is an essential trace element, but hexavalent chromium (Cr(VI)) is very toxic and carcinogenic.
Characteristics:
Chromium is a silver, lustrous, very hard metal that can take a high mirror polish. It is also odorless, tasteless, and malleable.
The metal forms a thin protective oxide coating in air, and burns when heated to form green chromium oxide(Cr2O3).
Uses:
Chromium is used in stainless steel, and other alloys. Chromium plating, for example on cars and bicyles, produces a smooth, silver finish that is highly resistant to corrosion.
The metal is also widely used as a catalyst.
Chromium compounds are valued as pigments for their vivid green, yellow, red and orange colors.
Harmful effects:
Chromium metal is an essential trace element, but hexavalent chromium (Cr(VI)) is very toxic and carcinogenic.
Characteristics:
Chromium is a silver, lustrous, very hard metal that can take a high mirror polish. It is also odorless, tasteless, and malleable.
The metal forms a thin protective oxide coating in air, and burns when heated to form green chromium oxide(Cr2O3).
Uses:
Chromium is used in stainless steel, and other alloys. Chromium plating, for example on cars and bicyles, produces a smooth, silver finish that is highly resistant to corrosion.
The metal is also widely used as a catalyst.
Chromium compounds are valued as pigments for their vivid green, yellow, red and orange colors.
Reactions & Compounds
Reaction with air: none
Reaction with 15 M HNO3: passivated
Oxide(s): CrO2, CrO3, Cr2O3 (chromia) + non-stoich
Hydride(s): CrH
Reaction with 15 M HNO3: passivated
Oxide(s): CrO2, CrO3, Cr2O3 (chromia) + non-stoich
Hydride(s): CrH
Reaction with 6 M HCl: mild, ⇒ H2, CrCl3
Reaction with 6 M NaOH:
Chloride(s): CrCl2, CrCl3
Reaction with 6 M NaOH:
Chloride(s): CrCl2, CrCl3
Radius
Atomic radius: 140 pm
Ionic radius (2+ ion): 90.5 pm
Ionic radius (2- ion): pm
Ionic radius (2+ ion): 90.5 pm
Ionic radius (2- ion): pm
Ionic radius (1+ ion): pm
Ionic radius (3+ ion): 75.5 pm
Ionic radius (1- ion): pm
Ionic radius (3+ ion): 75.5 pm
Ionic radius (1- ion): pm
Conductivity
Thermal conductivity: 93.9 W m-1 K-1
Electrical conductivity: 7.9 x 106 S m-1
Abundance & Isotopes
Abundance earth's crust: 102 parts per million by weight, 40 parts per million by moles
Abundance solar system: 20 parts per million by weight, 0.4 parts per million by moles
Cost, pure: $32 per 100g
Cost, bulk: $0.28 per 100g
Source: Chromium is not found as a free element in nature but is found in the form of ores. The main ore of chromium is chromite (FeCr2O4).
To isolate the metal commercially, chromite ore is oxidized to chromium(III) oxide (Cr2O3). The metal is then obtained by heating the oxide in the presence of aluminum or silicon.
Isotopes: Chromium has 21 isotopes whose half-lives are known, with mass numbers 42 to 63. Of these, three are stable, 52Cr, 53Cr and 54Cr. The most abundant is 52Cr at 83.8%.
Abundance solar system: 20 parts per million by weight, 0.4 parts per million by moles
Cost, pure: $32 per 100g
Cost, bulk: $0.28 per 100g
Source: Chromium is not found as a free element in nature but is found in the form of ores. The main ore of chromium is chromite (FeCr2O4).
To isolate the metal commercially, chromite ore is oxidized to chromium(III) oxide (Cr2O3). The metal is then obtained by heating the oxide in the presence of aluminum or silicon.
Isotopes: Chromium has 21 isotopes whose half-lives are known, with mass numbers 42 to 63. Of these, three are stable, 52Cr, 53Cr and 54Cr. The most abundant is 52Cr at 83.8%.
References
1. Mary Elvira Weeks, Discovery of the Elements V., Journal of Chemical Education, March 1932 p 470.
2. Per Enghag, Encyclopedia of the elements: technical data, history, processing, applications.,p 577- 578, John Wiley and Sons, 2004
2. Per Enghag, Encyclopedia of the elements: technical data, history, processing, applications.,p 577- 578, John Wiley and Sons, 2004
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