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The Element Barium

[Click for Isotope Data]





Atomic Number: 56

Atomic Weight: 137.327

Melting Point: 1000 K (727°C or 1341°F)

Boiling Point: 2170 K (1897°C or 3447°F)

Density: 3.62 grams per cubic centimeter

Phase at Room Temperature: Solid

Element Classification: Metal

Period Number: 6    Group Number: 2    Group Name: Alkaline Earth Metal

What's in a name? From the Greek word for heavy, barys.

Say what? Barium is pronounced as BAR-ee-em.

History and Uses:

Barium was first isolated by Sir Humphry Davy, an English chemist, in 1808 through the electrolysis of molten baryta (BaO). Barium is never found free in nature since it reacts with oxygen in the air, forming barium oxide (BaO), and with water, forming barium hydroxide (Ba(OH)2) and hydrogen gas (H2). Barium is most commonly found as the mineral barite (BaSO4) and witherite (BaCO3) and is primarily produced through the electrolysis of barium chloride (BaCl2).

Barium is used as a getter, a material that combines with and removes trace gases from vacuum tubes.

Barium sulfate (BaSO4), a common barium compound, is used as a filler for rubber, plastics and resins. It can be combined with zinc oxide (ZnO) to make a white pigment known as lithophone or with sodium sulfate (Na2SO4) to make another white pigment known as blanc fixe. Stones made from impure barium sulfate glow when exposed to light and will glow in the dark for up to six years if intensely heated in the presence of charcoal. These stones, known as Bologna stones, were discovered near Bologna, Italy in the early 1500s and were thought to possess magical properties by alchemists. Although all barium compounds are poisonous, barium sulfate can be safely ingested since it does not dissolve in water. It is also a good absorber of X-rays and, when swallowed, can be used to produce X-ray images of the intestinal tract.

Barium carbonate (BaCO3), another common barium compound, is used in the manufacture of ceramics and some types of glass. It is a component in clay slurries used in drilling oil wells. Barium carbonate is used to purify some chemical solutions and is the primary base material for the manufacture of other barium compounds.

Barium forms several other useful compounds. Barium nitrate (Ba(NO3)2) burns with a bright green color and is used in signal flares and fireworks. Barium chloride (BaCl) is used as a water softener. Barium oxide (BaO) easily absorbs moisture and is used as a desiccant. Barium peroxide (BaO2) forms hydrogen peroxide (H2O2) when it is mixed with water and is used as a bleaching agent that activates when wet. Barium titanate (BaTiO3) is used as a dielectric material in capacitors. Barium ferrite (BaO·6Fe2O3) is used to make magnets.

Barium-137m, a radioactive form of barium produced by the decay of cesium-137, has a relatively short half-life and is commonly used in high school and college physics half-life determination experiments.

Estimated Crustal Abundance: 4.25×102 milligrams per kilogram

Estimated Oceanic Abundance: 1.3×10-2 milligrams per liter

Number of Stable Isotopes: 6   (View all isotope data)

Ionization Energy: 5.212 eV

Oxidation States: +2

Electron Shell Configuration:


2s2   2p6

3s2   3p6   3d10

4s2   4p6   4d10

5s2   5p6