barium

caesium ← barium → lanthanum Sr ↑ Ba ↓ Ra 56Ba Periodic table
Appearance
silvery white
General properties
Name, symbol, number	barium, Ba, 56
Element category	alkaline earth metals
Group, period, block	2, 6, s
Standard atomic weight	137.33 g·mol−1
Electron configuration	[Xe] 6s2
Electrons per shell	2, 8, 18, 18, 8, 2 (Image)
Physical properties
Phase	solid
Density (near r.t.)	3.51 g·cm−3
Liquid density at m.p.	3.338 g·cm−3
Melting point	1000 K, 727 °C, 1341 °F
Boiling point	2170 K, 1897 °C, 3447 °F
Heat of fusion	7.12 kJ·mol−1
Heat of vaporization	140.3 kJ·mol−1
Specific heat capacity	(25 °C) 28.07 J·mol−1·K−1
Vapor pressure
P/Pa 1 10 100 1 k 10 k 100 k at T/K 911 1038 1185 1388 1686 2170
Atomic properties
Oxidation states	2 (strongly basic oxide)
Electronegativity	0.89 (Pauling scale)
Ionization energies	1st: 502.9 kJ·mol−1
	2nd: 965.2 kJ·mol−1
	3rd: 3600 kJ·mol−1
Atomic radius	222 pm
Covalent radius	215±11 pm
Van der Waals radius	268 pm
Miscellanea
Crystal structure	body-centered cubic
Magnetic ordering	paramagnetic
Electrical resistivity	(20 °C) 332 nΩ·m
Thermal conductivity	(300 K) 18.4 W·m−1·K−1
Thermal expansion	(25 °C) 20.6 µm·m−1·K−1
Speed of sound (thin rod)	(20 °C) 1620 m/s
Young's modulus	13 GPa
Shear modulus	4.9 GPa
Bulk modulus	9.6 GPa
Mohs hardness	1.25
CAS registry number	7440-39-3
Most stable isotopes
Main article: Isotopes of barium
iso NA half-life DM DE (MeV) DP 130Ba 0.106% 130Ba is stable with 74 neutrons 132Ba 0.101% 132Ba is stable with 76 neutrons 133Ba syn 10.51 y ε 0.517 133Cs 134Ba 2.417% 134Ba is stable with 78 neutrons 135Ba 6.592% 135Ba is stable with 79 neutrons 136Ba 7.854% 136Ba is stable with 80 neutrons 137Ba 11.23% 137Ba is stable with 81 neutrons 138Ba 71.7% 138Ba is stable with 82 neutrons
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Barium (pronounced /ˈbɛəriəm/, BAIR-ee-əm) is a chemical element. It has the symbol Ba, atomic number 56, and is the fifth element in Group 2. Barium is a soft silvery metallic alkaline earth metal. It is never found in nature in its pure form due to its reactivity with air. 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 are the very insoluble barium sulfate, BaSO₄ (barite), and barium carbonate, BaCO₃ (witherite). Benitoite is a rare gem containing barium.

Metallic barium has few industrial uses, but has been historically used to scavenge air in vacuum tubes. Barium compounds impart a green color to flames and have been used in fireworks. Barium sulfate is used for its heaviness, insolubility, and X-ray opacity. It is used as an insoluble heavy mud-like paste when drilling oil wells, and in purer form, as an X-ray radiocontrast agent for imaging the human gastrointestinal tract. Soluble barium compounds are poisonous due to release of the soluble barium ion, and have been used as rodenticides. New uses for barium continue to be found: it is an essential ingredient in "high temperature" YBCO superconductors.

Characteristics

Physical

Barium is a soft and ductile metal. Its simple compounds are notable for their relatively high (for an alkaline earth element) 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).

Chemical

Barium reacts exothermically with oxygen at room temperature to form barium oxide and peroxide. The reaction is violent if barium is powdered. It also reacts violently with dilute acids, alcohol and water

Ba + 2 H₂O → Ba(OH)₂ + H₂ (g)

At elevated temperatures, barium combines with chlorine, nitrogen and hydrogen to produce BaCl₂, Ba₃N₂ and BaH₂, respectively. Barium reduces oxides, chlorides and sulfides of less reactive metals. For example:

Ba + CdO → BaO + Cd

Ba + ZnCl₂ → BaCl₂ + Zn

3 Ba + Al₂S₃ → 3 BaS + 2 Al

When heated with nitrogen and carbon, it forms the cyanide:

Ba + N₂ + 2 C → Ba(CN)₂

Barium combines with several metals, including aluminium, zinc, led and tin, forming intermetallic compounds and alloys.^[1]

Isotopes

Naturally occurring barium is a mix of seven stable isotopes, the most abundant being ¹³⁸Ba (71.7 %). There are twenty-two isotopes known, but most of these are highly radioactive and have half-lives in the several millisecond to several day range. The only notable exceptions are ¹³³Ba which has a half-life of 10.51 years, and ^137mBa (2.55 minutes).^[2]

History

Name barium originates from Greek bary, meaning "heavy". Alchemists in the early Middle Ages knew about some barium minerals. Smooth pebble-like stones of mineral barite found in Bologna, Italy were known as "Bologna stones". After exposed to light they would glow for years that attracted them to witches and alchemists.^[3]

Carl Scheele identified barite in 1774, but did not isolate barium. Barium was isolated, as ions in solution, in 1808 by Sir Humphry Davy in England. The oxidized barium 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.^[3]

Occurrence and production

Barite

Trend in world production of barite

The abundance of barium is 0.0425 % in the Earth's crust and 13 µg/L in sea water. It occurs in the minerals barite (as the sulfate) and witherite (as the carbonate).^[1] Large deposits of barite are found in China, Germany, India, Morocco, and in the US.^[4]

Because barium quickly becomes oxidized in air, it is difficult to obtain this metal in its pure form. It is primarily found in and extracted from barite. Because barite is so insoluble, it cannot be used directly for the preparation of other barium compounds. Instead, the ore is heated with carbon to reduce it to barium sulfide:^[5]

BaSO₄ + 2 C → BaS + 2 CO₂

The barium sulfide is then hydrolyzed or treated with acids to form other barium compounds, such as the chloride, nitrate, and carbonate.

Barium is commercially produced through the electrolysis of molten barium chloride (BaCl₂):

(cathode) Ba²⁺ + 2 e⁻ → Ba

(anode) 2 Cl^– → Cl₂ (g) + 2 e⁻

Barium metal is also obtained by the reduction of barium oxide with finely divided aluminium at temperatures between 1100 and 1200 °C:

4 BaO + 2 Al → BaO·Al₂O₃ + 3 Ba (g)

The barium vapor is cooled by means of a water jacket and condensed into the solid metal. The solid block may be cast into rods or extruded into wires. Being a flammable solid, it is packaged under argon in steel containers or plastic bags.^[1]

Applications

Amoebiasis as seen in radiograph of barium-filled colon

Green barium fireworks

The most important use of elemental barium is as a scavenger removing last traces of oxygen and other gases in television and other electronic tubes. Besides, an isotope of barium, ¹³³Ba, is routinely used as a standard source in the calibration of gamma-ray detectors in nuclear physics studies.^[1]

Barium is an important component of YBCO superconductors. An alloy of barium with nickel is used in spark plug wire. Barium oxide is used in a coating for the electrodes of fluorescent lamps, which facilitates the release of electrons.

Barium compounds, and especially barite (BaSO₄), are extremely important to the petroleum industry. Besides,

• Barite is used in rubber production and in drilling mud, a weighting agent in drilling new oil wells.^[4]
• Barium sulfate is used as a radiocontrast agent for X-ray imaging of the digestive system ("barium meals" and "barium enemas").^[4] 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.^[6]
• Barium carbonate is a rat poison and can also be used in making bricks. Unlike the sulfate, the carbonate dissolves in stomach acid, allowing it to be poisonous. Barium carbonate is also used in glassmaking. Being a heavy element, barium increases the refractive index and luster of the glass.^[4]
• Barium nitrate and chlorate give green colors in fireworks.^[7]
• 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 tracer ammunition and as a bleaching agent.^[8]
• Barium titanate was proposed in 2007 to be used in next generation battery technology for electric cars.^[9]
• Barium fluoride is used for optics in infrared applications, since it is transparent from about 0.15 to 12 microns.^[10]
• Barium strontium niobate is used in large scale outdoors holgraphic displays as a "screen". When projected with blue laser light images are 3-D and very realistic.^[11]

Precautions

Barium powder is pyrophoric - it can explode in contact with air or oxidizing gases. It is likely to explode when combined with halogenated hydrocarbon solvents. It reacts violently with water. 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.^[1]

Barium sulfate can be taken orally because it is highly insoluble in water, and is eliminated completely from the digestive tract.^[1] Unlike other heavy metals, barium does not bioaccumulate.^[12][13] However, inhaled dust containing barium compounds can accumulate in the lungs, causing a benign condition called baritosis.^[14]

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 acetate could lead to death in high doses. Marie Robards poisoned her father with the substance in Texas in 1993. She was tried and convicted in 1996.^[15]

References

External links

Wikimedia Commons has media related to: Barium

Look up barium in Wiktionary, the free dictionary.

• WebElements.com – Barium
• Elementymology & Elements Multidict
• 3-D Holographic Display Using Strontium Barium Niobate
•  "Barium". Encyclopædia Britannica (11th ed.). 1911.