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Barium (Ba)
Barium (symbol Ba) is the chemical element with atomic number 56: an alkaline earth metal, solid at 0 °C, with an atomic mass of 137.33 u. Discovered in 1808 (Humphry Davy).
Barium is a reactive alkaline earth metal whose name comes from the Greek barys, “heavy,” because of the density of its ore, barite. Barite is used mainly to weigh down oil-drilling muds. Its sulfate, insoluble and therefore harmless, is swallowed by patients to make the digestive tract visible on X-rays.
Key facts
- Atomic number
- 56
- Symbol
- Ba
- French name
- Baryum
- Atomic mass
- 137.33 u
- Molar mass
- 137.33 g/mol
- Family
- Alkaline earth metals
- Position
- period 6, group 2, s-block
- State at 0 °C
- Solid
- Melting point
- 726.9 °C
- Boiling point
- 1,844.9 °C
- Density
- 3.51 g/cm³
- Electronegativity (Pauling)
- 0.89
- First ionization energy
- 503 kJ/mol
- Atomic radius
- 215 pm
- Electron configuration
- [Xe] 6s²
- Abundance in Earth's crust
- 425 ppm (14th most abundant element)
- Indicative price
- 0.26 $/kg (order of magnitude)
- Radioactive
- no
- Discovery
- 1808, Humphry Davy
Origin of the name
From the Greek barys, heavy.
What does barium look like?
A soft, silvery-white metal that oxidizes very quickly in air and reacts with water. It is stored under oil or inert gas.
Where is barium found?
About 425 ppm of Earth's crust, a relatively common element. It mostly forms barite (barium sulfate), often in veins or alongside lead-zinc deposits.
Natural sources
- Barite (baryte)
- Witherite
How is barium produced?
Barite is quarried and then ground; about 7 to 8 million tonnes are produced each year. The metal, little used, is obtained by reducing barium oxide with aluminium.
Top producers
- China
- India
- Morocco
- Iran
- Kazakhstan
What is barium used for?
- Oil and gas drilling muds weighted with barite (main use).
- Digestive contrast agent (“barium meal”).
- The green of fireworks.
- White pigment and filler for paints, paper and plastics.
- X-ray shielding (barite concrete and plaster).
In everyday life
- Stomach or bowel X-ray
- Green firework
- White paint and glossy paper
- Radiology room wall
Role in living things
No biological role. Barium sulfate is harmless because it does not dissolve, but soluble barium salts are true poisons for the muscles and heart.
Hazards of barium
Soluble compounds (chloride, carbonate) are toxic: they block the potassium channels of cells and cause paralysis and heart rhythm disorders. Barium carbonate has been used as rat poison.
Cosmic origin
- Dying stars: Made slowly in red giants (stars like the Sun at the end of their lives).
- Neutron stars: Created when two neutron stars collide — the “forge” of gold.
History of barium
Around 1602, Vincenzo Casciarolo, a shoemaker and alchemist from Bologna, noticed that a stone glowed in the dark after being heated: this was the “Bologna stone,” a barite. In 1774, Carl Wilhelm Scheele identified “baryta” as a new earth, and Humphry Davy isolated the metal by electrolysis in 1808.
Did you know?
- The Bologna stone was one of the first phosphorescent materials studied scientifically, in the 17th century.
- In 1986, Bednorz and Müller discovered high-temperature superconductivity in a lanthanum barium copper oxide; they received the Nobel Prize as early as 1987.
- Not all “desert roses” are gypsum: some are made of barite.
Isotopes of barium
Six stable isotopes, plus barium-130, with a vanishingly faint radioactivity. It was by finding barium in uranium bombarded with neutrons that Otto Hahn discovered fission in 1938.
- barium-130: 0.106% of natural barium, radioactive, half-life 2.2 × 10²¹ years
- barium-132: 0.101% of natural barium, stable
- barium-133: radioactive, half-life 10.6 years. Calibration source for gamma-ray detectors.
- barium-134: 2.417% of natural barium, stable
- barium-135: 6.592% of natural barium, stable
- barium-136: 7.854% of natural barium, stable
- barium-137: 11.232% of natural barium, stable
- barium-137m: radioactive, half-life 2.55 min. Born from caesium-137, it is what actually emits the gamma rays credited to caesium.
- barium-138: 71.698% of natural barium, stable
- barium-140: radioactive, half-life 12.8 days. The fission product identified by Hahn and Strassmann in 1938.
Related elements
Same family (alkaline earth metals): Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), Radium (Ra).
Same column (group 2): Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), Radium (Ra).