Barium is a metallic element, soft, and when pure is silvery white like lead. The metal oxidises very easily and it reacts with water or alcohol. Barium is one of the alkaline-earth metals. Small amounts of barium compounds are used in paints and glasses.
Barium salts impart green colours to flames. The picture above shows the colour arising from adding barium chlorate (BaClO3) to a burning mixture (only to be carried out by a professionally qualified chemist).
Image adapted with permission fromProf James Marshall's (U. North Texas, USA)Walking Tour of the elements CD.
Barium has no biological role. The British Pharmaceutical Codex from 1907 indicates that barium chloride ["barii chloridum", BaCl2.2H2O] has a stimulant action on the heart and other muscles. It was said that it "raises blood pressure by constricting the vessels and tends to empty the intestines, bladder, and gall bladder". Its poisonous nature was also pointed out. Barium sulphide (BaS) was used as a depilatory agent (removes hair). Barium sulphate (BaSO4) is insoluble and used for body imaging (barium meal).
Isotope abundances of barium with the most intense signal set to 100%.
Barium isotopes are used in a wide variety of fields and applications. Ba-130 is used in the production of Ba-131/Cs-131 which is used in brachytherapy (seeds). Ba-132 can be used for the production of Ba-133 which is used as a gamma reference source. Ba-134 has been used to perform experiments in the field of nuclear physics. Ba-136 has been used to study photon scattering phenomena. Both Ba-136 and Ba-138 have been used in activation cross section experiments. Ba-135 has been used to validate the use of spinor symmetry while Ba-137 has been used in experiments regarding the theory of relativistic coupled clusters. Finally, Ba-138 has been used in studying so-called r- and s-processes in stars.
Isolation: barium metal is available commercially and there is normally no need to make it in the laboratory. Commercially, it is made on small scale by the electrolysis of molten barium chloride, BaCl2.
cathode: Ba2+(l) + 2e- → Ba
anode: Cl-(l) →1/2Cl2 (g) + e-
Barium metal can also be islated from the reduction of barium oxide, BaO, with aluminium.
Density of solid: 3510 kg m-3
Molar volume: 38.16 cm3
Thermal conductivity: 18 W m‑1 K‑1
Melting point: 1000 [727 °C (1341 °F)] K
Boiling point: 2143 [1870 °C (3398 °F)] K
Enthalpy of fusion: 20.5 kJ mol-1
Atomic radius (empirical): 215 pm
Molecular single bond covalent radius: 196 (coordination number 2) ppm
van der Waals radius: 303 ppm
Pauling electronegativity: 0.89 (Pauling units)
Allred Rochow electronegativity: 0.97 (Pauling units)
Mulliken-Jaffe electronegativity: 0.88 (sp orbital)
First ionisation energy: 502.85 kJ mol‑1
Second ionisation energy: 965.22 kJ mol‑1
Third ionisation energy: 3458.40 kJ mol‑1
Universe: 10 ppb by weight
Crustal rocks: 340000 ppb by weight
Human: 300 ppb by weight
