Chromium
Chromium General
| Name:Chromium | Symbol:Cr |
| Type:Transition Metal | Atomic weight:51.996 |
| Density @ 293 K:7.19 g/cm3 | Atomic volume:7.23 cm3/mol |
|
Discovered:
Chromium was discovered in 1780 by Nicolas-Louis Vanquelin. He isolated chromium by heating the oxide in a charcoal oven. Vanquelin also identified small amounts of chromium in ruby and emerald stones. Chromium was named from the Greek word 'chroma', meaning color because it forms a variety of colorful compounds. |
|
Chromium States
| State (s, l, g):solid | |
| Melting point:2180 K (1907 °C) | Boiling point:2943 K (2670 °C) |
Chromium Energies
| Specific heat capacity: 0.45 J g-1 K-1 | Heat of atomization:397 kJ mol-1 |
| Heat of fusion:21.0 kJ mol-1 | Heat of vaporization :339.5 kJ mol-1 |
| 1st ionization energy:652.8 kJ mol-1 | 2nd ionization energy:1592 kJ mol-1 |
| 3rd ionization energy:2987.2 kJ mol-1 | Electron affinity:64.3 kJ mol-1 |
Chromium Oxidation & Electrons
| Shells: 2,8,13,1 | Electron configuration:[Ar] 3d5 4s1 |
| Minimum oxidation number: -2 | Maximum oxidation number:6 |
| Min. common oxidation no.:0 | Max. common oxidation no.:3 |
| Electronegativity (Pauling Scale):1.66 | Polarizability volume:11.6 Å3 |
Chromium Appearance & Characteristics
| Structure: bcc: body-centered cubic | Color:silver-gray |
| Hardness: 8.5 mohs | |
|
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. 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. |
|
Chromium Reactions
| Reaction with air:none | Reaction with 6 M HCl:mild, ⇒ H2, CrCl3 |
| Reaction with 15 M HNO3: passivated | Reaction with 6 M NaOH: |
Chromium Compounds
| Oxide(s):CrO2, CrO3, Cr2O3 (chromia) + non-stoich | Chloride(s):CrCl2, CrCl3 |
| Hydride(s):CrH |
Chromium Radius
| Atomic radius:140 pm | Ionic radius (1+ ion):pm |
| Ionic radius (2+ ion):90.5 pm | Ionic radius (3+ ion):75.5 pm |
| Ionic radius (2- ion):pm | Ionic radius (1- ion):pm |
Chromium Conductivity
| Thermal conductivity:93.9 W m-1 K-1 | Electrical conductivity:7.9 x 106 S m-1 |
Chromium 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%. |
|
Chromium Other
|
Other:
|
|
Prev: Vanadium Next: Manganese |