Chemical element, symbol Ba and atomic number 56 / From Wikipedia, the free encyclopedia

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Barium is a chemical element; it has symbol Ba and atomic number 56. It is the fifth element in group 2 and is a soft, silvery alkaline earth metal. Because of its high chemical reactivity, barium is never found in nature as a free element.

Quick facts: Barium, Pronunciation, Appearance, Standard a...
Barium, 56Ba
Pronunciation/ˈbɛəriəm/ (BAIR-ee-əm)
Appearancesilvery gray; with a pale yellow tint[1]
Standard atomic weight Ar°(Ba)
Barium in the periodic table


Atomic number (Z)56
Groupgroup 2 (alkaline earth metals)
Periodperiod 6
Block  s-block
Electron configuration[Xe] 6s2
Electrons per shell2, 8, 18, 18, 8, 2
Physical properties
Phase at STPsolid
Melting point1000 K (727 °C, 1341 °F)
Boiling point2118 K (1845 °C, 3353 °F)
Density (near r.t.)3.51 g/cm3
when liquid (at m.p.)3.338 g/cm3
Heat of fusion7.12 kJ/mol
Heat of vaporization142 kJ/mol
Molar heat capacity28.07 J/(mol·K)
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K) 911 1038 1185 1388 1686 2170
Atomic properties
Oxidation states+1, +2 (a strongly basic oxide)
ElectronegativityPauling scale: 0.89
Ionization energies
  • 1st: 502.9 kJ/mol
  • 2nd: 965.2 kJ/mol
  • 3rd: 3600 kJ/mol
Atomic radiusempirical: 222 pm
Covalent radius215±11 pm
Van der Waals radius268 pm
Color lines in a spectral range
Spectral lines of barium
Other properties
Natural occurrenceprimordial
Crystal structure body-centered cubic (bcc)
Body-centered cubic crystal structure for barium
Speed of sound thin rod1620 m/s (at 20 °C)
Thermal expansion20.6 µm/(m⋅K) (at 25 °C)
Thermal conductivity18.4 W/(m⋅K)
Electrical resistivity332 nΩ⋅m (at 20 °C)
Magnetic orderingparamagnetic[4]
Molar magnetic susceptibility+20.6×10−6 cm3/mol[5]
Young's modulus13 GPa
Shear modulus4.9 GPa
Bulk modulus9.6 GPa
Mohs hardness1.25
CAS Number7440-39-3
DiscoveryCarl Wilhelm Scheele (1772)
First isolationHumphry Davy (1808)
Isotopes of barium
Main isotopes[6] Decay
abun­dance half-life (t1/2) mode pro­duct
130Ba 0.11% (0.5–2.7)×1021 y εε 130Xe
132Ba 0.1% stable
133Ba synth 10.51 y ε 133Cs
134Ba 2.42% stable
135Ba 6.59% stable
136Ba 7.85% stable
137Ba 11.2% stable
138Ba 71.7% stable
Symbol_category_class.svg Category: Barium
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The most common minerals of barium are barite (barium sulfate, BaSO4) and witherite (barium carbonate, BaCO3). The name barium originates from the alchemical derivative "baryta", from Greek βαρὺς (barys), meaning 'heavy'. Baric is the adjectival form of barium. Barium was identified as a new element in 1772, but not reduced to a metal until 1808 with the advent of electrolysis.

Barium has few industrial applications. Historically, it was used as a getter for vacuum tubes and in oxide form as the emissive coating on indirectly heated cathodes. It is a component of YBCO (high-temperature superconductors) and electroceramics, and is added to steel and cast iron to reduce the size of carbon grains within the microstructure. Barium compounds are added to fireworks to impart a green color. Barium sulfate is used as an insoluble additive to oil well drilling fluid. In a purer form it is used as X-ray radiocontrast agents for imaging the human gastrointestinal tract. Water-soluble barium compounds are poisonous and have been used as rodenticides.

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