Barium
2008/9 Schools Wikipedia Selection. Related subjects: Chemical elements
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 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 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Specific heat capacity | (25 °C) 28.07 J·mol−1·K−1 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 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 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 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.
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 in drilling mud, a weighting agent in drilling new oil wells.
- Barium sulfate is used as a radiocontrast agent for X-ray imaging 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 dissolves in stomach acid, allowing it to be poisonous.
- An alloy 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.
- 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 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 tracer ammunition.
- Barium titanate was proposed in 2007 to be used in next generation battery technology for electric cars.
- Barium Fluoride is used in infrared applications.
- Barium is a key element in YBCO superconductors.
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.
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
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):
Compounds
The most important compounds are barium peroxide, barium chloride, sulfate, carbonate, nitrate, and chlorate.
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-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).
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. 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.