Barium

For other uses, see Barium (disambiguation).

56 caesium ← barium → lanthanum Sr ↑ Ba ↓ Ra 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)
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).

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).

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.

History

Barium (Greek "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.

Compounds

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

See also barium compounds.

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).

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.

External links

• WebElements.com – Barium
• Elementymology & Elements Multidict
• Periodic Table table
• Chemistry Explained on Barium

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