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 18:21, 19 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, protecting it from oxidation by the air, it should be kept under a petroleum-based fluid (such as kerosene) or other suitable oxygen-free liquid that excludes air.

The compounds of barium, particularly the water-soluble ones, are toxic. In addition, as barium is a heavy element, its compounds 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

Some of the important compounds of barium are noted below. Their uses are mentioned under Applications.

Barium carbonate

As noted above, barium carbonate (BaCO₃) can be found in nature in the form of the mineral witherite. It is the chief source of barium salts.

Barium carbonate reacts with various acids to form soluble barium salts. For example, it reacts with hydrochloric acid (HCl) to produce barium chloride:

BaCO₃(s) + 2 HCl(aq) → BaCl₂(aq) + CO₂(g) + H₂O(l)

The reaction with sulfuric acid, however, is poor, because barium sulfate is highly insoluble.

Barium chloride

Barium chloride (BaCl₂) is a highly toxic, ionic, water-soluble salt of barium. It imparts a yellow-green coloration to a flame.

In water solution, it can react with sulfate ions (SO₄^2-) to produce a thick white precipitate of barium sulfate. The reaction is as follows.

BaCl₂(aq) + SO₄^2-(aq) → BaSO₄(s) + 2Cl^-(aq)

Barium hydroxide

Barium hydroxide, also known as baryta, is a strong, corrosive chemical base. It has a white granular or powdery appearance. It may be prepared by dissolving barium oxide (BaO) in water. It crystallizes as the octahydrate, which may be converted to the monohydrate by heating in air or completely dehydrated at 100 °C in a vacuum. The monohydrate is the usual commercial form.

Barium sulfate

Barium sulfate (or barium sulphate) is a white crystalline solid with the formula BaSO₄. It is very insoluble in water and other potential solvents. As mentioned above, the mineral barite is composed largely of barium sulfate.

Applications

Barium and its compounds have a number of applications:

Metallic barium is a "getter" in vacuum tubes, to remove the last traces of oxygen.
An alloy of barium with nickel is used in sparkplug wire.
Barium compounds, and especially barite (barium sulfate), 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 medical diagnostic work to obtain X-ray images of the digestive system (through "barium meals" and "barium enemas"). Although the water-soluble compounds of barium are often highly toxic, the extremely low solubility of barium sulfate protects the patient from absorbing harmful amounts of barium.
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 sulfate is used as a filler in plastics.
Barium carbonate is used for the preparation of rat poison and in the manufacture of glass, porcelain, bricks, and cement.
Barium oxide is used in coating the cathodes of fluorescent lamps and cathode ray tubes, as it facilitates the release of electrons.
As a chemical base, barium hydroxide is used clean up acid spills and make them significantly less harmful. It is also used in the laboratory for the titration of weak acids, and for reactions such as the hydrolysis of esters and nitriles.
Under the name baryta, barium hydroxide is used in homeopathic remedies.
In the laboratory, a barium chloride solution (in water) is used to test for the presence of sulfate ions. If sulfate is present, a white precipitate of barium sulfate is produced. By a similar reaction, barium chloride can be used to prepare other insoluble salts, such as barium oxalate (BaC₂O₄).
In industry, barium chloride is mainly used in the purification of brine solution in caustic chlorine plants and in the manufacture of heat-treatment salts, pigments, and other barium salts.
The salts of barium (particularly its nitrate, chloride, and chlorate) may be used in fireworks to produce green colors.
Impure barium sulfide phosphoresces after exposure to light.
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]

References
ISBN links support NWE through referral fees

N. N. Greenwood, A. Earnshaw, Chemistry of the Elements, Pergamon Press, Oxford, UK, 1984.
Handbook of Chemistry and Physics, 71st edition, CRC Press, Ann Arbor, Michigan, 1990.
H. Nechamkin, The Chemistry of the Element, McGraw-Hill, New York, 1968.

External links

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@@ Line 97: / Line 97: @@
 In [[water]] solution, it can react with [[sulfate]]* ions (SO<sub>4</sub><sup>2-</sup>) to produce a thick white [[precipitate]]* of [[barium sulfate]]*. The reaction is as follows.
 :BaCl<sub>2</sub>(aq)  +  SO<sub>4</sub><sup>2-</sup>(aq)  →  BaSO<sub>4</sub>(s)  +  2Cl<sup>-</sup>(aq)
-This property is used as a test for the presence of sulfate ions. By a similar reaction, barium chloride can be used to prepare other insoluble salts, such as barium oxalate (BaC<sub>2</sub>O<sub>4</sub>). In industry, barium chloride is mainly used in the purification of [[brine]]* solution in caustic chlorine plants and in the manufacture of heat-treatment salts,  pigments, and other barium salts. It may also be used in [[fireworks]]* to give a bright green color. Its toxicity, however, limits its applicability.
 === Barium hydroxide ===
-Barium hydroxide, also known as ''baryta'', is a strong chemical base with a white granular or powdery appearance. It may be prepared by dissolving [[barium oxide]] (BaO) in water. It crystallizes as the octahydrate, which may be converted to the monohydrate by heating in air or completely dehydrated at 100 °C in a vacuum. The [[Hydrate|monohydrate]] is the usual commercial form.
+Barium hydroxide, also known as ''baryta'', is a strong, corrosive chemical base. It has a white granular or powdery appearance. It may be prepared by dissolving [[barium oxide]] (BaO) in water. It crystallizes as the octahydrate, which may be converted to the monohydrate by heating in air or completely dehydrated at 100 °C in a vacuum. The [[Hydrate|monohydrate]] is the usual commercial form.
-Barium hydroxide is used in analytical chemistry for the titration of [[weak acid]]s,
-particularly [[organic acid]]s.
-Barium hydroxide is used in organic synthesis as a strong base, for example for the
-hydrolysis of esters and nitriles.
-It is also used to clean up acid spills and make them significantly less harmful.
-Under the name baryta it is used in homeopathic remedies.
-==== Safety ====
-Barium hydroxide presents the same hazards as other strong bases and as other water-soluble barium compounds: it is corrosive and toxic.
 === Barium sulfate ===
 Barium sulfate (or barium sulphate) is a white crystalline solid with the formula BaSO<sub>4</sub>. It is very insoluble in [[water]] and other potential solvents. As mentioned above, the mineral [[barite]]* is composed largely of barium sulfate.
-Barium sulfate is frequently used clinically as a [[radiocontrast]]* agent for [[X ray|X-ray]] [[Medical imaging|imaging]]*, especially of the [[gastrointestinal tract]]*. Although the water-soluble compounds of barium are often highly toxic, the extremely low solubility of barium sulfate protects the patient from absorbing harmful amounts of barium.
-Barium sulfate mixtures are used as white pigment for paints, and may be combined with [[zinc oxide]]* (ZnO) or [[sodium sulfate]]* (Na<sub>2</sub>SO<sub>4</sub>).
-Barium sulfate is also used as a high temperature oxidizer in certain pyrotechnic formulas, as it produces a green-colored light while it burns. Barium nitrate is more common in green pyrotechnic formulas, as it is a more amiable oxidizer while still producing green colored light.
-Barium sulfate is used as a filler in plastics and as a component of [[oil well]] drilling fluid to increase the density.
--------
-* [[barium peroxide]], [[barium chloride|chloride]], [[barium sulfate|sulfate]], [[barium carbonate|carbonate]], [[barium nitrate|nitrate]], and [[barium chlorate|chlorate]].
 == Applications ==
-Barium and its compounds have some medical and many industrial uses:
+Barium and its compounds have a number of applications:
-*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.
+*Metallic barium is a "[[getter]]" in vacuum tubes, to remove the last traces of [[oxygen]].
-*[[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.
 *An alloy of barium with [[nickel]] is used in [[sparkplug]]* wire.
+*Barium compounds, and especially barite (barium sulfate), 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 ray]]s and is used in medical diagnostic work to obtain X-ray images of the digestive system (through "[[barium meal]]*s" and "[[barium enema]]*s"). Although the water-soluble compounds of barium are often highly toxic, the extremely low solubility of barium sulfate protects the patient from absorbing harmful amounts of barium.
+*[[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 sulfate is used as a filler in plastics.
+* Barium carbonate is used for the preparation of rat poison and in the manufacture of [[glass]], porcelain, bricks, and cement.
 *[[Barium oxide]]* is used in coating the [[cathode]]*s of [[fluorescent lamp]]*s and cathode ray tubes, as it facilitates the release of [[electron]]s.
-*Metallic barium is a "[[getter]]" in vacuum tubes, to remove the last traces of [[oxygen]].
+* As a chemical base, barium hydroxide is used clean up acid spills and make them significantly less harmful. It is also used in the laboratory for the titration of [[weak acid]]s, and for reactions such as the hydrolysis of esters and nitriles.
-*[[Barium carbonate]]* is used in [[glass]]making. Being a heavy element, barium increases the [[refractive index]] and luster of the glass.
+* Under the name ''baryta'', barium hydroxide is used in homeopathic remedies.
-*[[Barite]] is used extensively as a weighting agent in [[oil well]]* drilling fluids and in [[rubber]]* production.
+* In the laboratory, a barium chloride solution (in water) is used to test for the presence of sulfate ions. If sulfate is present, a white precipitate of barium sulfate is produced. By a similar reaction, barium chloride can be used to prepare other insoluble salts, such as barium oxalate (BaC<sub>2</sub>O<sub>4</sub>).
-*When used in fireworks, [[barium nitrate]] and [[barium chlorate|chlorate]] give green colors.
+* In industry, barium chloride is mainly used in the purification of [[brine]]* solution in caustic chlorine plants and in the manufacture of heat-treatment salts, pigments, and other barium salts.
-*Impure [[barium sulfide]] [[phosphorescence|phosphoresces]] after exposure to [[light]].
+* The salts of barium (particularly its nitrate, chloride, and chlorate) may be used in fireworks to produce green colors.
-*[[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.
+*Impure [[barium sulfide]]* [[phosphorescence|phosphoresces]] after exposure to [[light]].
 *[[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.