Difference between revisions of "Barium" - New World Encyclopedia

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== Occurrence and production ==
 
== Occurrence and production ==
  
Barium rapidly becomes oxidized in air, making it difficult to find this metal in its pure form. It is primarily found in and extracted from the [[mineral]] [[barite]], which is crystalized barium sulfate.
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It is difficult to find barium in its pure form in nature, as it rapidly becomes oxidized in air. It is primarily found in and extracted from the [[mineral]] [[barite]]*, a crystalline form of barium sulfate.
  
Barium is commercially produced through the [[electrolysis]] of molten [[barium chloride]] (BaCl<sub>2</sub>)
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Barium is commercially produced through the [[electrolysis]] of molten [[barium chloride]]* (BaCl<sub>2</sub>). Barium ions (Ba<sup>2+</sup>) migrate to the cathode, where they gain electrons (e<sup>&minus;</sup>) and are converted to metallic barium. At the same time, chloride ions (Cl<sup>&minus;</sup>) migrate to the anode, where they lose electrons and are converted to chlorine gas. The reactions at the electrodes can be written as follows:
''Isolation'' (* follow):<br />
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:At the cathodeBa<sup>2+</sup> + 2[[electron|e<sup>&minus;</sup>]] &rarr; Ba
:([[cathode]]) Ba<sup>2+</sup>* + 2[[electron|e<sup>-</sup>]] &rarr; Ba ([[anode]]) Cl<sup>-</sup>* &rarr; ½Cl<sub>2</sub> ([[gas|g]]) + e<sup>-</sup>
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:At the anode:  2Cl<sup>&minus;</sup> &rarr; Cl<sub>2</sub> (gas) + 2e<sup>&minus;</sup>
  
== Discovery ==
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== Discovery and etymology ==
  
Barium (from the [[Greek language|Greek]] word ''barys'', meaning "heavy") was first identified in 1774 by [[Carl Scheele]]* and extracted in 1808 by Sir [[Humphry Davy]] in [[England]]. The oxide was at first called ''barote'', by [[Guyton de Morveau]], which was changed by [[Antoine Lavoisier]] to baryta, from which "barium" was derived to describe the metal.
+
Barium (from the [[Greek language|Greek]] word ''barys'', meaning "heavy") was first identified in 1774 by [[Carl Scheele]]* and extracted in 1808 by Sir [[Humphry Davy]] in [[England]]. The oxide was initially called ''barote'', by [[Guyton de Morveau]]. [[Antoine Lavoisier]] changed the name to ''baryta'', from which "barium" was derived to describe the metal.
  
 
== Notable characteristics ==
 
== Notable characteristics ==

Revision as of 18:55, 18 September 2006

For other uses, see Barium (disambiguation).
56 caesiumbariumlanthanum
Sr

Ba

Ra
Ba-TableImage.png
periodic table
General
Name, Symbol, Number barium, Ba, 56
Chemical series alkaline earth metals
Group, Period, Block 2, 6, s
Appearance silvery white
Ba,56.jpg
Atomic mass 137.327(7) g/mol
Electron configuration [Xe] 6s2
Electrons per shell 2, 8, 18, 18, 8, 2
Physical properties
Phase solid
Density (near r.t.) 3.51 g/cm³
Liquid density at m.p. 3.338 g/cm³
Melting point 1000 K
(727 °C, 1341 °F)
Boiling point 2170 K
(1897 °C, 3447 °F)
Heat of fusion 7.12 kJ/mol
Heat of vaporization 140.3 kJ/mol
Heat capacity (25 °C) 28.07 J/(mol·K)
Vapor pressure
P/Pa 1 10 100 1 k 10 k 100 k
at T/K 911 1038 1185 1388 1686 2170
Atomic properties
Crystal structure cubic body centered
Oxidation states 2
(strongly basic oxide)
Electronegativity 0.89 (Pauling scale)
Ionization energies 1st: 502.9 kJ/mol
2nd: 965.2 kJ/mol
3rd: 3600 kJ/mol
Atomic radius 215 pm
Atomic radius (calc.) 253 pm
Covalent radius 198 pm
Miscellaneous
Magnetic ordering paramagnetic
Electrical resistivity (20 °C) 332 nΩ·m
Thermal conductivity (300 K) 18.4 W/(m·K)
Thermal expansion (25 °C) 20.6 µm/(m·K)
Speed of sound (thin rod) (20 °C) 1620 m/s
Speed of sound (thin rod) (r.t.) 13 m/s
Shear modulus 4.9 GPa
Bulk modulus 9.6 GPa
Mohs hardness 1.25
CAS registry number 7440-39-3
Notable isotopes
Main article: Isotopes of barium
iso NA half-life DM DE (MeV) DP
130Ba 0.106% Ba is stable with 74 neutrons
132Ba 0.101% Ba is stable with 76 neutrons
133Ba syn 10.51 y ε 0.517 133Cs
134Ba 2.417% Ba is stable with 78 neutrons
135Ba 6.592% Ba is stable with 79 neutrons
136Ba 7.854% Ba is stable with 80 neutrons
137Ba 11.23% Ba is stable with 81 neutrons
138Ba 71.7% Ba is stable with 82 neutrons

Barium (chemical symbol Ba, atomic number 56) is a soft, silvery chemical element classified as an alkaline earth metal. Given its reactivity with air, it is never found in its pure form in nature. Its oxide is historically known as baryta, but it reacts with water and carbon dioxide and is not found as a mineral. The most common naturally occurring minerals of barium are the very insoluble barite (barium sulfate, BaSO4) and witherite (barium carbonate, BaCO3).

Occurrence and production

It is difficult to find barium in its pure form in nature, as it rapidly becomes oxidized in air. It is primarily found in and extracted from the mineral barite, a crystalline form of barium sulfate.

Barium is commercially produced through the electrolysis of molten barium chloride (BaCl2). Barium ions (Ba2+) migrate to the cathode, where they gain electrons (e) and are converted to metallic barium. At the same time, chloride ions (Cl) migrate to the anode, where they lose electrons and are converted to chlorine gas. The reactions at the electrodes can be written as follows:

At the cathode: Ba2+ + 2e → Ba
At the anode: 2Cl → Cl2 (gas) + 2e

Discovery and etymology

Barium (from the Greek word barys, meaning "heavy") was first identified in 1774 by Carl Scheele and extracted in 1808 by Sir Humphry Davy in England. The oxide was initially called barote, by Guyton de Morveau. Antoine Lavoisier changed the name to baryta, from which "barium" was derived to describe the metal.

Notable characteristics

Barium is a metallic element that is chemically similar to calcium but more reactive. This metal oxidizes very easily when exposed to air and is highly reactive with water or alcohol, producing hydrogen gas. Burning in air or oxygen produces not just barium oxide (BaO) but also the peroxide. Simple compounds of this heavy element are notable for their high specific gravity. This is true of the most common barium-bearing mineral, its sulfate barite BaSO4, also called 'heavy spar' due to the high density (4.5 g/cm3).

Isotopes

Naturally occurring barium is a mix of seven stable isotopes. There are twenty-two isotopes known, but most of these are highly radioactive and have half-lifes in the several millisecond to several minute range. The only notable exceptions are 133Ba which has a half-life of 10.51 years, and 137mBa (2.6 minutes).

Compounds

The most important compounds are barium peroxide, chloride, sulfate, carbonate, nitrate, and chlorate.

Applications

Barium has some medical and many industrial uses:

  • Barium compounds, and especially barite (BaSO4), are extremely important to the petroleum industry. Barite is used as a weighting agent in drilling new oil wells. A weighting agent is a material that adds body to petroleum.
  • Barium sulfate is also a good X-ray absorber, used in X-ray diagnostic work for obtaining images of the digestive system ("barium meals" and "barium enemas").
  • Barium carbonate is a useful rat poison and can also be used in making bricks. Unlike the sulfate, the carbonate disolves in stomach acid, allowing it to be poisonous.
  • An alloy with nickel is used in sparkplug wire.
  • Barium oxide is used in a coating for the electrodes of fluorescent lamps, which facilitates the release of electrons.
  • The metal is a "getter" in vacuum tubes, to remove the last traces of oxygen.
  • Barium carbonate is used in glassmaking. Being a heavy element, barium increases the refractive index and luster of the glass.
  • Barite is used extensively as a weighting agent in oil well drilling fluids and in rubber production.
  • Barium nitrate and chlorate give green colors in fireworks.
  • Impure barium sulfide phosphoresces after exposure to the light.
  • Lithopone, a pigment that contains barium sulfate and zinc sulfide, is a permanent white that has good covering power, and does not darken in when exposed to sulfides.
  • Barium peroxide can be used as a catalyst to start an aluminothermic reaction when welding rail tracks together. It can also be used in green tracers for bullets.


Precautions

All water or acid soluble barium compounds are extremely poisonous. At low doses, barium acts as a muscle stimulant, while higher doses affect the nervous system, causing cardiac irregularities, tremors, weakness, anxiety, dyspnea and paralysis. This may be due to its ability to block potassium ion channels which are critical to the proper function of the nervous system.

Barium sulfate can be used in medicine only because it does not dissolve, and is eliminated completely from the digestive tract. Unlike other heavy metals, barium does not bioaccumulate. [1] However, inhaled barium dust can accumulate in the lungs, a condition called baritosis.

Oxidation occurs very easily and, to remain pure, barium should be kept under a petroleum-based fluid (such as kerosene) or other suitable oxygen-free liquids that exclude air.

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