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Atomic Mass of Barium

May 6, 2013

 Basic Information

Name: Barium
Symbol: Ba
Atomic Number: 56
Atomic Mass: 137.327 amu
Melting Point: 725.0 °C (998.15 K, 1337.0 °F)
Boiling Point: 1140.0 °C (1413.15 K, 2084.0 °F)
Number of Protons/Electrons: 56
Number of Neutrons: 81
Classification: Alkaline Earth
Crystal Structure: Cubic
Density @ 293 K: 3.51 g/cm3
Color: Silver

Atomic Structure

[Bohr  Model of Barium] Number of Energy Levels: 6
First Energy Level:


Second Energy Level:


Third Energy Level:


Fourth Energy Level:


Fifth Energy Level:


Sixth Energy Level:



Isotope Half Life
Ba-130 Stable
Ba-131 11.7 days
Ba-132 Stable
Ba-133 10.5 years
Ba-133m 1.6 days
Ba-134 Stable
Ba-135 Stable
Ba-135m 1.2 days
Ba-136 Stable
Ba-137 Stable
Ba-137m 2.6 minutes
Ba-138 Stable
Ba-139 1.4 hours
Ba-140 12.8 days
Ba-141 18.3 minutes
Ba-142 10.7 minutes


Date of Discovery: 1808
Discoverer: Sir Humphrey Davy
Name Origin: From the Greek word barys (heavy)
Uses: Medical applications, among others
Obtained From: barytine, whiterite


Barium – Ba

DiscoveryBarium was discovered by Sir Humphry Davy in 1808 in London.


Barium is a relatively soft, silvery-white metal resembling lead. It oxidises very easily and is therefore stored under petroleum or in an inert gas atmosphere.


Barium occurs only in combination with other elements, chiefly in the ores barytes and witherite. It can be prepared by electrolysis of the chloride, or by heating barium oxide with aluminium.


Barium is not an extensively used element. The best-known use is in the form of barium sulfate, which can be drunk as a medical cocktail to outline the stomach and intestines for medical examination. The sulfate is also used in paint and in glassmaking.

Barium carbonate has been used as a rat poison. Barium nitrate gives fireworks a green colour.

Biological Role

Barium and all its compounds that are water or acid soluble are toxic.

General Information

Barium combines with air, and reacts rapidly with water and alcohol.

Physical Information
Atomic Number 56
Relative Atomic Mass (12C=12.000) 137.33
Melting Point/K 1002
Boiling Point/K 1910
Density/kg m-3 3594 (293K)
Ground State Electron Configuration [Xe]6s2
Electron Affinity(M-M)/kJ mol-1 +46
Key Isotopes
nuclide 130Ba 132Ba 133Ba 134Ba 135Ba
atomic mass 129.9 131.9 133.9 134.9
natural abundance 0.106% 0.101% 0% 2.417% 6.592%
half-life stable stable 10.53 yrs stable stable
nuclide 136Ba 137Ba 138Ba 140Ba
atomic mass 135.9 136.9 137.9
natural abundance 7.854% 11.32% 71.7% 0%
half-life stable stable stable 12.7 days
Other Information
Enthalpy of Fusion/kJ mol-1 7.66
Enthalpy of Vaporisation/kJ mol-1 150.9
Oxidation States
Ionisation Energies/kJ mol-1
M – M+ 502.8
M+ – M2+ 965.1
M2+ – M3+ 3600
M3+ – M4+ 4700
M4+ – M5+ 6000
M5+ – M6+ 7700
M6+ – M7+ 9000
M7+ – M8+ 10200
M8+ – M9+ 13500
M9+ – M10+ 15100

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