Barium

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For other uses, see Barium (disambiguation).
56 caesium ← barium → lanthanum
Sr
↑
Ba
↓
Ra
General
Name, Symbol, Number barium, Ba, 56
Chemical series alkaline earth metals
Group, Period, Block 2, 6, s
Appearance silvery white
Standard atomic weight 137.327(7)  g·mol−1
Electron configuration [Xe] 6s2
Electrons per shell 2, 8, 18, 18, 8, 2
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
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
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 n Ω·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
Selected 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
References

Barium (pronounced /ˈbɛəriəm/) is a chemical element. It has the symbol Ba, and atomic number 56. 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.

Contents

[edit] 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).

[edit] Applications

Barium has some medical and many industrial uses:

[edit] 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.

[edit] Occurrence

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 the mineral barite which is crystallized barium sulfate. 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[1]

BaSO4 + 2C → BaS + 2CO2

The barium sulfide is then hydrolyzed or reacted 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) Isolation (* follow):

(cathode) Ba2+* + 2e- → Ba
(anode) Cl-* → ½Cl2 (g) + e-

[edit] Compounds

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

[edit] Isotopes

Main article: isotopes of barium

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-lives 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 (2.55 minutes).

[edit] 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 taken orally because it is highly insoluble in water, and is eliminated completely from the digestive tract. Unlike other heavy metals, barium does not bioaccumulate.[2] However, inhaled dust containing barium compounds can accumulate in the lungs, causing a benign 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.

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.

[edit] References

  1. ^ Toxicological Profile for Barium and Barium Compounds. Agency for Toxic Substances and Disease Registry, CDC. 2007. [1]
  2. ^ Toxicity Profiles, Ecological Risk Assessment | Region 5 Superfund | US EPA

[edit] External links

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