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Element Fact
In 1961, the International Union of Pure and Applied Chemistry adopted the isotope carbon-12 as the basis of atomic weight, which has a mass of exactly 12.000 atomic mass unit.

Barium, Ba

barium sample

Atomic number: 56
Atomic mass: 137.327(7)
Natural abundance: 390 ppm
130Ba (129.906310) - 0.106%
132Ba (131.905056) - 0.101%
134Ba (133.904503) - 2.417%
135Ba (134.905683) - 6.592%
136Ba (135.904570) - 7.854%
137Ba (136.905821) - 11.23%
138Ba (137.905241) - 71.70%

History and Production

Derived from Greek barys, meaning heavy. Its minerals had been known since the seventeenth century. It was until around 1774-1779 C.W. Scheele and independently J.G. Gahn showed that the heavy spa was in fact barite (BaSO4) and baryta, distinguished from lime, was in fact the oxide of barium. The metal was isolated by H. Davy in 1808 from baryta. It is now mined mainly from barite where the metal is extracted by high-temperature reduction with aluminium. It can also be obtained by electrolysis of fused chloride. The metal is used as a getter in vacuum tubes and is used as an alloy with nickel for making spark-plug wire. The sulfate compound BaSO4 is used mainly as a heavy mud slurry in oilwell drilling. The compound also gives a permanent white is used in paint, and in X-ray diagnostic work. The carbonate, on the other hand, is used as a rat poison.

Physical Data

barytes or barite mineral
It is a soft silvery white metal. It readily reacts with air and water and is normally kept under petroleum. The metal is widely distributed which consists of about 390 ppm in earth's crust. It exists as mineral compounds such as barite (or barytes), and witherite (BaCO3). The mineral barytes is usually white but frequently discolored by contaminants, as the one shown on the left.

Interatomic distance: 434.8 pm
Melting point: 727C
Boiling point: 1897C
Thermal conductivity/Wm-1K-1: 18.4 (27C)
Density/kgm-3: 3594 (20C), 3325 (m.p.)

Standard Thermodynamic Data (atomic gas)

Enthalpy of formation: 180.0 kJ/mol
Gibbs free energy of formation: 146 kJ/mol
Entropy: 170.2 J/mol K
Heat capacity: 20.8 J/mol K

Electronic data

Electronic configuration: [Xe] 6s2
Term symbol: 1S0
Electron affinity: 13.9537 kJ/mol   Electronegativity (Pauline): 0.89
Ionization energy (first, second, third): 502.85, 965.23, - kJ/mol

Chemical properties

Chemical behavior of barium is quite similar to calcium but more reactive. For instance, finely divided barium inflames in air. The hydrides are more easily formed than that of calcium. Hydrogen can react with barium even at room temperature to for barium hydride, BaH2.

Test for barium
(1) Flame test gives apple green color.
(2) Ammonium carbonate gives a white precipitate of barium carbonate.
(3) Barium-containing solution gives a yellow precipitate of barium chromate when potassium chromate is added.

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