56BaBarium137.327 u
Barium (Ba)
Barium is an alkaline earth metal with atomic number 56, in period 6 and group 2 of the periodic table. Its atomic mass is 137.327 u and its electron configuration is [Xe] 6s². Solid at 25 °C.
Key facts
| Atomic number | 56 |
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| Atomic mass | 137.327 u |
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| Category | Alkaline Earth Metal |
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| Period | 6 |
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| Group | 2 |
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| Block | s |
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| Electron configuration | [Xe] 6s² |
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| Electrons per shell | 2, 8, 18, 18, 8, 2 |
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| Electronegativity (Pauling) | 0.89 |
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| Oxidation states | +1, +2common in bold |
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| State at 25 °C | Solid |
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| Melting point | 1000 K726.85 °C |
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| Boiling point | 2170 K1896.85 °C |
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| Density | 3.62 g/cm³ |
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Atomic properties
| First ionization energy | 5.212 eV |
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| Electron affinity | 13.95 kJ/mol |
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| Atomic radius | 222 pm |
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| Covalent radius | 215 pm |
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| Van der Waals radius | 268 pm |
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| Common ions | Ba²⁺ |
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| Protons, neutrons, electrons | 56, 81, 56 |
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Physical and thermal properties
| Molar volume | 38.16 cm³/mol |
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| Heat of fusion | 8 kJ/mol |
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| Heat of vaporization | 140 kJ/mol |
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| Specific heat | 205 J/(kg·K) |
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| Thermal conductivity | 18 W/(m·K) |
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| Thermal expansion | 2.06 × 10⁻⁵ K⁻¹ |
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| Mohs hardness | 1.25 |
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| Young’s modulus | 13 GPa |
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| Crystal structure | Body-centered cubic |
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| Magnetic type | Paramagnetic |
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Identification and history
| CAS number | 7440-39-3 |
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| Latin name | Barium |
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| Discovered by | Carl Wilhelm Scheele · 1772 |
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| Named by | --- |
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Natural isotopes
| Isotope | Mass (u) | Abundance |
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| 130Ba | 129.906326 | 0.11 % |
| 132Ba | 131.905061 | 0.1 % |
| 134Ba | 133.904508 | 2.42 % |
| 135Ba | 134.905688 | 6.59 % |
| 136Ba | 135.904576 | 7.85 % |
| 137Ba | 136.905827 | 11.23 % |
| 138Ba | 137.905247 | 71.7 % |
Data checked against PubChem (NIH), IUPAC, the NIST Atomic Spectra Database and the IAEA (NUBASE and AME), the same data you see in the app.
A dash (---) means there is no reliable published measurement. The app never makes one up.
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Periodic Table