24 vanadium ← chromium → manganese
- ↑ Cr ↓ Mo
Periodic table - Extended periodic
Name, symbol, number
chromium, Cr, 24
Group, period, block
6, 4, d
Standard atomic weight
51.9961(6) g·mol −1
[Ar] 3d 5 4s 1
Electrons per shell
2, 8, 13, 1
Density (near r.t.)
7.15 g·cm −3
Liquid density at m.p.
6.3 g·cm −3
2180 K (1907 °C, 3465 °F)
2944 K (2671 °C, 4840 °F)
Heat of fusion
21.0 kJ·mol −1
Heat of vaporization
339.5 kJ·mol −1
(25 °C) 23.35 J·mol −1·K −1
cubic body centered
6, 4, 3, 2 (strongly acidic oxide)
1.66 (Pauling scale)
(more) 1st: 652.9 kJ·mol −1
2nd: 1590.6 kJ·mol −1
3rd: 2987 kJ·mol −1
Atomic radius (calc.)
AFM (rather: SDW)
(20 °C) 125 nΩ·m
(300 K) 93.9 W·m −1·K −1
(25 °C) 4.9 µm·m −1·K −1
Speed of sound (thin rod)
(20 °C) 5940 m/s
CAS registry number
Main article: Isotopes of chromium
Cr is stable with 28 neutrons
Cr is stable with 29 neutrons
Cr is stable with 30 neutrons
Chromium is a chemical element in the periodic table that
has the symbol Cr and atomic number 24. It is a steel-gray, lustrous, hard metal
that takes a high polish and has a high melting point. It is also odourless,
tasteless, and malleable. Occurence
Chromium is mined as chromite (FeCr
2O 4) ore. About
two-fifths of the chromite ores and concentrates in the world are produced in
South Africa. Kazakhstan, India, Russia and Turkey are also substantial
producers. Untapped chromite deposits are plentiful, but geographically
concentrated in Kazakhstan and southern Africa.
Approximately 15 million tons of marketable chromite ore were produced in
2000, and converted into approximately 4 million tons of ferro-chrome with an
approximate market value of 2.5 billion United States dollars.
Though native chromium deposits are rare, some native chromium metal has been
discovered. The Udachnaya Mine in Russia produces samples of the native metal.
This mine is a kimberlite pipe rich in diamonds, and the reducing environment so
provided helped produce both elemental chromium and diamond. (See also chromium
Chromium is obtained commercially by heating the ore in the presence of
aluminium or silicon.
Chromium is a member of the transition metals, in group 6. Chromium(0) has an
electronic configuration of 4s
13d 5, due to the lower
energy of the high spin configuration. Chromium exhibits a wide range of
possible oxidation states. The most common oxidation states of chromium are +2,
+3, and +6, with +3 being the most stable. +1, +4 and +5 are rare. Chromium
compounds of oxidation state +6 are powerful oxidants.
Chromium is passivated by oxygen, forming a thin (usually a few atoms thick
being transparent because of thickness) protective oxide surface layer with
another element such as nickel, and/or iron. It forms a compound called a spinal
structure which, being very dense, prevents diffusion of oxygen into the
underlying layer. (In iron or plain carbon steels the oxygen actually migrates
into the underlying material.) Chromium is usually plated on top of a nickel
layer which may or may not have been copper plated first. Chromium as opposite
to most other metals such as iron and nickel does not suffer from hydrogen
embrittlement. It does though suffer from nitrogen embrittlement and hence no
straight chromium alloy has ever been developed. Below the pourbaix diagram can
be seen, it is important to understand that the diagram only displays the
thermodynamic data and it does not display any details of the rates of
On 26 July 1761, Johann Gottlob Lehmann found an orange-red mineral in the
Ural Mountains which he named
Siberian red lead. Though misidentified as
a lead compound with selenium and iron components, the material was in fact
lead chromate with a formula of PbCrO 4, now known as the
In 1770, Peter Simon Pallas visited the same site as Lehmann and found a red
"lead" mineral that had very useful properties as a pigment in paints. The use
of Siberian red lead as a paint pigment developed rapidly. A bright yellow made
from crocoite became a color in fashion.
In 1797, Louis Nicolas Vauquelin received samples of crocoite ore. He was
able to produce chromium oxide with a chemical formula of CrO
mixing crocoite with hydrochloric acid. In 1798, Vauquelin discovered that he
could isolate metallic chromium by heating the oxide in a charcoal oven. He was
also able to detect traces of chromium in precious gemstones, such as ruby, or
emerald. Later that year he successfully isolated chromium atoms.
During the 1800s chromium was primarily used as a component of paints and in
tanning salts but now metal alloys account for 85% of the use of chromium. The
remainder is used in the chemical industry and refractory and foundry
Chromium was named after the Greek word "Chrôma" meaning color, because of
the many colorful compounds made from it.
Potassium dichromate is a powerful oxidizing agent and is the preferred
compound for cleaning laboratory glassware of any trace organics. It is used as
a saturated solution in concentrated sulfuric acid for washing the apparatus.
For this purpose, however, sodium dichromate is sometimes used because of its
higher solubility (5 g/100 ml vs. 20 g/100 ml respectively). Chrome green is the
green oxide of chromium, Cr
2O 3, used in enamel painting,
and glass staining. Chrome yellow is a brilliant yellow pigment,
PbCrO 4, used by painters.
Chromic acid has the hypothetical structure H
Neither chromic nor dichromic acid is found in nature, but their anions are
found in a variety of compounds. Chromium trioxide, CrO 3, the acid
anhydride of chromic acid, is sold industrially as "chromic acid".
Chromium and the quintuple bond
The compound synthesized by Nguyen, which
was determined experimentally to contain a Cr-Cr quintuple
Chromium is notable for its ability to form quintuple covalent bonds. The
synthesis of a compound of chromium(I) and a hydrocarbon radical was shown via
X-ray diffraction to contain a quintuple bond of length 183.51(4) pm (1.835
angstroms) joining the two central chromium atoms.
 This was accomplished through the use of an extremely bulky
monodentate ligand which through its sheer size prevents further coordination.
Chromium currently remains the only element for which quintuple bonds have been
Uses of chromium:
In metallurgy, to impart corrosion resistance and a shiny finish:
as an alloy constituent, such as in stainless steel in cutlery
in chrome plating,
in anodized aluminium, literally turning the surface of aluminium into ruby.
As dyes and paints :
Chromium(III) oxide is a metal polish known as green rouge.
Chromium salts color glass an emerald green.
Chromium is what makes a ruby red, and therefore is used in producing
also makes a brilliant yellow for painting As a catalyst.
Chromite is used to make molds for the firing of bricks.
Chromium salts are used in the tanning of leather.
Potassium dichromate is a chemical reagent, used in cleaning laboratory
glassware and as a titrating agent. It is also used as a mordant (i.e., a fixing
agent) for dyes in fabric.
Chromium(IV) oxide (CrO 2) is used to manufacture magnetic tape,
where its higher coercivity than iron oxide tapes gives better performance.
In well drilling muds as an anti-corrosive.
In medicine, as a dietary supplement or slimming aid, usually as chromium
(III) chloride or chromium(III) picolinate.
Chromium hexacarbonyl (Cr(CO) 6) is used as a gasoline additive.
Chromium boride (CrB) is used as a high-temperature electrical conductor.
Chromium (III) sulfate (Cr 2(SO 4) 3) is used
as a green pigment in paints, in ceramic, varnishes and inks as well as in
Chromium (VI) is used in the post Ballard preparation of Gravure
(rotogravure) printing Forme Cylinders. By electroplating the metal onto the
second coat of copper (after the Ballard skin), the longevity of the printing
cylinder is increased.
Micronutrient, in "health" aware drinks, known to improve the amount of
energy you get from food.
Zookeeper - 2007-12-08 02:42:08