Difference between revisions of "Barium" - New World Encyclopedia

Vapor pressure
56	caesium ← barium → lanthanum
	periodic table
General
Name, Symbol, Number	barium, Ba, 56
Chemical series	alkaline earth metals
Group, Period, Block	2, 6, s
Appearance	silvery white ;
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)
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

Revision as of 19:53, 18 September 2006

For other uses, see Barium (disambiguation).

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, metallic 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 (BaSO₄).

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

As a member of the family of alkaline earth metals, barium lies in group 2 (former group 2A) of the periodic table, between strontium and radium. In addition, it is placed in period 6, between cesium and lanthanum.

Barium is chemically similar to calcium but is more reactive. This metal readily oxidizes when exposed to air and is highly reactive with water or alcohol, producing hydrogen gas. Upon burning in air or oxygen, it produces not just barium oxide (BaO) but also barium peroxide.

To store barium in its pure form, preventing it from becoming oxidized by air, it should be kept under a petroleum-based fluid (such as kerosene) or other suitable oxygen-free liquid that excludes air.

Simple compounds of this heavy element are notable for their high specific gravity (density). For example, barite, the most common barium-bearing mineral, is also called "heavy spar" based on its high density (4.5 g/cm³).

Isotopes

Naturally occurring barium is a mix of seven stable isotopes. There are 22 known isotopes, but most of them are highly radioactive, with half-lives in the range of several milliseconds to several minutes. The only notable exceptions are ¹³³Ba, with 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 and its compounds have 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 absorber of X rays and is used in X-ray diagnostic work to obtain images of the digestive system (through "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 of barium with nickel is used in sparkplug wire.
Barium oxide is used in coating the electrodes of fluorescent lamps, as it facilitates the release of electrons.
Metallic barium 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.
When used in fireworks, barium nitrate and chlorate give green colors.
Impure barium sulfide phosphoresces after exposure to 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

Barium dust, if inhaled, can accumulate in the lungs, leading to a condition called baritosis. In addition, barium compounds that are soluble in water or acid 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 the result of its ability to block potassium ion channels, which are critical to the proper functioning 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 (accumulate in the bodies of living systems). [1]

External links

Credits

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@@ Line 54: / Line 54: @@
 == 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.
+It is difficult to find barium in its pure, metallic 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 (BaSO<sub>4</sub>).
 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:
@@ Line 66: / Line 66: @@
 == Notable characteristics ==
-Barium is a [[metal]]lic element that is chemically similar to [[calcium]] but more reactive. This metal [[oxidation|oxidizes]] very easily when exposed to air and is highly [[chemical reaction|reactive]] with [[water (molecule)|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]] BaSO<sub>4</sub>, also called 'heavy spar' due to the high density (4.5 g/cm<sup>3</sup>).
+As a member of the family of alkaline earth metals, barium lies in group 2 (former group 2A) of the periodic table, between strontium and radium. In addition, it is placed in period 6, between cesium and lanthanum.
+Barium is chemically similar to [[calcium]] but is more reactive. This metal readily [[oxidation|oxidizes]] when exposed to air and is highly [[chemical reaction|reactive]] with [[water (molecule)|water]] or [[alcohol]], producing [[hydrogen]] gas. Upon burning in [[air]] or [[oxygen]], it produces not just [[barium oxide]]* (BaO) but also barium [[peroxide]]*.
+To store barium in its pure form, preventing it from becoming oxidized by air, it should be kept under a petroleum-based fluid (such as [[kerosene]]*) or other suitable [[oxygen]]-free liquid that excludes air.
+Simple compounds of this heavy element are notable for their high [[specific gravity]]* (density). For example, barite, the most common barium-bearing mineral, is also called "heavy spar" based on its high density (4.5 g/cm<sup>3</sup>).
 === Isotopes ===
-Naturally occurring barium is a mix of seven stable [[isotope]]s. There are twenty-two isotopes known, but most of these are highly [[radioactive]] and have [[half-life]]s in the several millisecond to several minute range. The only notable exceptions are <sup>133</sup>Ba which has a half-life of 10.51 years, and <sup>137m</sup>Ba (2.6 minutes).
+Naturally occurring barium is a mix of seven stable [[isotope]]s. There are 22 known isotopes, but most of them are highly [[radioactive]], with half-lives in the range of several milliseconds to several minutes. The only notable exceptions are <sup>133</sup>Ba, with a half-life of 10.51 years, and <sup>137m</sup>Ba (2.6 minutes).
 == Compounds ==
@@ Line 77: / Line 83: @@
 == Applications ==
-Barium has some medical and many industrial uses:
+Barium and its compounds have 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 meal]]s" and "[[barium enema]]s").
+*[[Barium sulfate]]* is also a good absorber of [[X ray]]s and is used in [[X-ray]] diagnostic work to obtain images of the digestive system (through "[[barium meal]]*s" and "[[barium enema]]*s").
-*[[Barium carbonate]] is a useful [[rat poison]] and can also be used in making [[brick]]s. Unlike the sulfate, the carbonate disolves in stomach acid, allowing it to be poisonous.
+*[[Barium carbonate]]* is a useful [[rat poison]]* and can also be used in making [[brick]]s. Unlike the sulfate, the carbonate disolves in stomach acid, allowing it to be poisonous.
-*An alloy with [[nickel]] is used in [[sparkplug]] wire.
+*An alloy of barium with [[nickel]] is used in [[sparkplug]]* wire.
-*[[Barium oxide]] is used in a coating for the [[electrode]]s of [[fluorescent lamp]]s, which facilitates the release of [[electron]]s.
+*[[Barium oxide]]* is used in coating the [[electrode]]*s of [[fluorescent lamp]]*s, as it facilitates the release of [[electron]]s.
-*The metal is a "[[getter]]" in vacuum tubes, to remove the last traces of [[oxygen]].
+*Metallic barium is a "[[getter]]" in vacuum tubes, to remove the last traces of [[oxygen]].
-*[[Barium carbonate]] is used in [[glass]]making. Being a heavy element, barium increases the [[refractive index]] and luster of the glass.
+*[[Barium carbonate]]* is used in [[glass]]making. 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.
+*[[Barite]] is used extensively as a weighting agent in [[oil well]]* drilling fluids and in [[rubber]]* production.
-*[[Barium nitrate]] and [[barium chlorate|chlorate]] give green colors in fireworks.
+*When used in fireworks, [[barium nitrate]] and [[barium chlorate|chlorate]] give green colors.
-*Impure [[barium sulfide]] [[phosphorescence|phosphoresces]] after exposure to the [[light]].
+*Impure [[barium sulfide]] [[phosphorescence|phosphoresces]] after exposure to [[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.
+*[[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.
+*[[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 [[poison]]ous. 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 [[bioaccumulation|bioaccumulate]]. [http://www.epa.gov/region5/superfund/ecology/html/toxprofiles.htm#ba]  However, inhaled barium dust can accumulate in the lungs, a condition called [[baritosis]].
+Barium dust, if inhaled, can accumulate in the lungs, leading to a condition called [[baritosis]]*. In addition, barium compounds that are soluble in water or acid are extremely [[poison]]ous. 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 the result of its ability to block [[potassium ion channels]]*, which are critical to the proper functioning of the nervous system.
-[[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.
+[[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 [[bioaccumulation|bioaccumulate]] (accumulate in the bodies of living systems). [http://www.epa.gov/region5/superfund/ecology/html/toxprofiles.htm#ba]
 == External links ==