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[General | States | Energies | Oxidation & Electrons]
[Appearance & Characteristics | Reactions | Other Forms]
[Radius | Conductivity
| Abundance | History]
| Name |
Chromium |
Symbol |
Cr |
| Atomic number |
24 |
Atomic weight |
51.996 |
| Density @ 293 K |
7.19 g/cm3 |
Atomic volume |
7.23 cm3/mol |
| Group |
Trans. Met. |
Discovered |
1798 |
| State (s, l, g) |
s |
| Melting point |
2130.2 K |
Boiling point |
2963 K |
| Heat of fusion |
16.90 kJ/mol |
Heat of vaporization |
344.30 kJ/mol |
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| 1st ionization energy |
652.8 kJ/mole |
Electronegativity |
1.66 |
| 2nd ionization energy |
1592 kJ/mole |
Electron affinity |
64.3 kJ/mole |
| 3rd ionization energy |
2987.2 kJ/mole |
Specific heat |
0.45 J/gK |
| Heat atomization |
397 kJ/mole atoms |
| Shells |
2,8,13,1 |
Electron configuration |
[Ar] 3d5 4s1 |
| Minimum oxidation number |
-2 |
Maximum oxidation number |
6 |
| Minimum common oxidation number |
0 |
Maximum common oxidation number |
6 |
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| Structure |
bcc: body-centered cubic |
Color |
silvery-white |
| Uses |
CrO2 tape, paint, steel |
Toxicity |
|
| Hardness |
9 mohs |
Characteristics |
hard |
| Reaction with air |
none |
Reaction with 6M HCl |
mild, =>H2, CrCl3 |
| Reaction with 6M HCl |
mild, =>H2, CrCl3 |
Reaction with 15M HNO3 |
passivated |
| Reaction with 6M NaOH |
|
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| Number of isotopes |
4 |
Hydride(s) |
CrH |
| Oxide(s) |
Cr2O3 CrO2 CrO3+non-stoich |
Chloride(s) |
CrCl2 CrCl3 |
| Ionic radius (2- ion) |
pm |
Ionic radius (1- ion) |
pm |
| Atomic radius |
128 pm |
Ionic radius (1+ ion) |
pm |
| Ionic radius (2+ ion) |
90.5 pm |
Ionic radius (3+ ion) |
75.5 pm |
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| Thermal conductivity |
93.9 J/m-sec-deg |
Electrical conductivity |
77.519 1/mohm-cm |
| Polarizability |
11.6 A^3 |
| Source |
Chromite (oxide) |
Rel. abund. solar system |
4.130 log |
| Abundance earth's crust |
2 log |
Cost, pure |
10 $/100g |
| Cost, bulk |
$/100g |
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History:
(Gr. chroma,
color) 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, 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 and the dichromates and the
potassium and ammonium chrome alums. 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. Chromium
compounds are toxic and should be handled with
proper safeguards.
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