barium (Ba)


Barium is a soft, silvery-white metallic element that readily tarnishes in air. It is one of the alkaline earth metals. It was discovered by Humphry Davy in 1808 and occurs chiefly as barite (barium sulfate, BaSO4) and as witherite (barium carbonate, BaCO3).


The compounds of barium resemble those of calcium but are poisonous. They are used in the manufacture of paints, glass, rodent poison, and fireworks, and as drying agents. Barium sulfate is swallowed to allow X-ray examination of the stomach and intestines because barium atoms are opaque to X-rays; this is called a "barium meal." The most common isotope is barium-138 (71.66 percent).


atomic number 56
relative atomic mass 137.34
relative density 3.51
melting point 725°C (1,337°F)
boiling point 1,640°C (2,984°F)