Barium (Ba)

Stable isotopes of barium available from ISOFLEX

Isotope Z(p) N(n) Atomic Mass Natural Abundance Enrichment Level Chemical Form
Ba-130  56  74  129.906311 0.11%  33.00%  Carbonate
Ba-132  56  76  131.905056 0.10% 12.80-40.70%  Carbonate
Ba-134 56 78 133.904504 2.42% 88.00% Carbonate
Ba-135 56 79 134.905684 6.59% >94.00% Carbonate
Ba-136 56 80 135.904571 7.85% 61.00-95.40% Carbonate
Ba-137 56 81 136.905822 11.23% 91.70% Carbonate
Ba-138 56 82 137.905242 71.70% 99.80% Carbonate

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Barium was discovered in 1808 by Sir Humphry Davy. Its name derives from the Greek word barys, meaning “heavy.”

A silvery-white, soft, ductile and somewhat malleable metal, barium gives off a green color in flame. It is extremely reactive and readily reacts with water, ammonia, halogens, oxygen and most acids. Barium metal reacts exothermically with oxygen at ambient temperatures, forming barium oxide; the reaction is especially violent when the metal is present in powder form. Barium also reacts violently with water, forming barium hydroxide and liberating hydrogen. It reacts violently with dilute acids, evolving hydrogen.

Barium is a strong reducing agent. It reduces oxidizing agents, reacting violently. It also combines with several metals — including aluminum, zinc, lead and tin — forming a wide range of intermetallic compounds and alloys.

The most important use of barium is as a scavenger in electronic tubes. The metal, often in powder form or as an alloy with aluminum, is employed to remove the last traces of gases from vacuum and television picture tubes. Alloys of barium have numerous applications, including battery performance and deoxidizing alloys to lower the oxygen content. Thin films of barium are used as lubricants on the rotors of anodes in vacuum x-ray tubes, as well as on alloys used for spark plugs. A few radioactive isotopes of barium find applications in nuclear reactions and spectrometry.

Finely divided barium powder is pyrophoric. It can explode in contact with air or oxidizing gases. It is likely to explode when mixed and stirred with halogenated hydrocarbon solvents. All barium salts, especially the water- and acid-soluble compounds, are highly toxic. Barium ion is a stimulant to the heart muscle and can cause death through ventricular fibrillation of the heart. Intake of a few grams of barium salt can be lethal to humans. The insoluble salts such as barium sulfate, however, have little toxic action.

Properties of Barium

Name Barium
Symbol Ba
Atomic number 56
Atomic weight 137.327
Standard state Solid at 298 ºK
CAS Registry ID 7440-39-3
Group in periodic table 2
Group name Alkaline earth metals
Period in periodic table 6
Block in periodic table s-block
Color Silvery white
Classification Metallic
Melting point 727 °C
Boiling point 1845 °C
Vaporization point 1897 ºC
Thermal conductivity 18.4 W/(m·K)
Electrical resistivity 332 µΩ·cm at 20°C
Electronegativity 0.9
Heat of vaporization 140.3 kJ·mol-1
Heat of fusion 8 kJ·mol-1
Density of liquid 3.338 g/cm3
Density of solid 3.51 g/cm3
Electron configuration [Xe]6s2
Atomic radius 222 pm
Ionic radius Ba2+ in crystal: 1.42 Å (coordination number 8)
Oxidation state +2 
First ionization potential 10.00 eV


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