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Barium,  56Ba
General properties
Name, symbol Barium, Ba
Appearance Silvery-white metal
Barium in the periodic table


Atomic number 56
Standard atomic weight (Ar) 137.327(7)
Group, block (alkaline earth metals); s-block
Period period 6
Electron configuration [Xe] 6s2
per shell
2, 8, 18, 18, 8, 2
Physical properties
Phase Solid
Melting point 1000 K ​(727 °C, ​​1341 °F)
Boiling point 2118 K ​(1845 °C, ​​3353 °F)
Density near r.t. 3.51 g/cm3
when liquid, at  3.338 g/cm3
Heat of fusion 7.12 kJ/mol
Heat of 142 kJ/mol
Molar heat capacity 28.07 J/(mol·K)
Atomic properties
Oxidation states +2, +1 ​(a strongly basic oxide)
Electronegativity Pauling scale: 0.89
energies 1st: 502.9 kJ/mol
2nd: 965.2 kJ/mol
3rd: 3600 kJ/mol
Atomic radius empirical: 222 pm
Covalent radius 215±11 pm
Van der Waals radius 268 pm
Crystal structure ​​body-centered cubic
Speed of sound thin rod 1620 m/s (at 20 °C)
Thermal expansion 20.6 µm/(m·K) (at 25 °C)
Thermal conductivity 18.4 W/(m·K)
Electrical resistivity 332 Ω·m (at 20 °C)
Magnetic ordering Paramagnetic
Young's modulus 13 GPa
Shear modulus 4.9 GPa
Bulk modulus 9.6 GPa
Mohs hardness 1.25
CAS Registry Number 7440-39-3
Discovery Carl Wilhelm Scheele (1772)
First isolation Humphry Davy (1808)
· references

Barium is a chemical element with symbol Ba and atomic number 56. It is the heaviest non-radioactive s-block element.



Barium slowly oxidizes in air to form a dark layer of barium oxide and barium nitride. Barium and its compounds burn with a green flame. This property allowed it to be used in green fireworks, though in recent years, boron compounds are beginning to replace barium, as they're less toxic.

Barium is readily attacked by acids, though reaction with sulfuric acid forms a protective insoluble layer of barium sulfate, which protects the metal from further corrosion.

Barium reacts with water to release hydrogen gas. Barium hydroxide precipitates:[1]

Ba + 2 H2O → Ba(OH)2 + H2

The same reaction also happens with alcohols, giving barium alkoxide.

Barium reacts with ammonia to form complexes such as Ba(NH3)6.


Barium is a silvery white metal, that rapidly turns black on exposure with air. Barium melts at 730 °C, intermediate between those of the lighter strontium (780 °C) and heavier radium (700 °C). Its boiling point of 1,900 °C is higher than that of strontium (1,382 °C) and radium (~1737 °C). Barium has a density of 3.62 g/cm3


Barium metal is sold by various chemical suppliers, either under oil or ampouled. GalliumSource sells 50 g of barium at a price of $92.00.


Barium can be isolated through the aluminothermic reduction of barium oxide:

4 BaO + 2 Al → 3 Ba↑ + BaAl2O4

Due to the high temperatures released during this reaction, the resulting barium metal turns to vapors, which are condensed under argon. This is not easy to do.

Silicon can also be used as a reducing agent.


  • Make barium peroxide
  • Make soluble barium salts
  • Green flame
  • Ellement collecting



Barium readily reacts with water releasing hydrogen gas, which is flammable and its build-up may cause explosions. However, unlike alkali metals, it can be safely handled with bare hand.

Soluble barium salts and other compounds are very toxic to organisms and should be handled with proper protection. Insoluble barium compounds however, are pretty much non-toxic .


Barium metal must be stored away from moisture, air and other corrosive vapors. It is best stored under mineral oil or ampouled, under argon.


Barium metal is best converted to barium sulfate, which is non-toxic.



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