37RbRubidium85.4678 u
Rubidium (Rb)
Rubidium is an alkali metal with atomic number 37, in period 5 and group 1 of the periodic table. Its atomic mass is 85.4678 u and its electron configuration is [Kr] 5s¹. Solid at 25 °C.
Key facts
| Atomic number | 37 |
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| Atomic mass | 85.4678 u |
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| Category | Alkali Metal |
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| Period | 5 |
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| Group | 1 |
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| Block | s |
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| Electron configuration | [Kr] 5s¹ |
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| Electrons per shell | 2, 8, 18, 8, 1 |
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| Electronegativity (Pauling) | 0.82 |
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| Oxidation states | −1, +1common in bold |
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| State at 25 °C | Solid |
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| Melting point | 312.46 K39.31 °C |
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| Boiling point | 961 K687.85 °C |
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| Density | 1.532 g/cm³ |
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Atomic properties
| First ionization energy | 4.177 eV |
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| Electron affinity | 46.9 kJ/mol |
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| Atomic radius | 248 pm |
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| Covalent radius | 220 pm |
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| Van der Waals radius | 303 pm |
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| Common ions | Rb⁺ |
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| Protons, neutrons, electrons | 37, 48, 37 |
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Physical and thermal properties
| Molar volume | 55.76 cm³/mol |
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| Heat of fusion | 2.19 kJ/mol |
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| Heat of vaporization | 71 kJ/mol |
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| Specific heat | 364 J/(kg·K) |
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| Thermal conductivity | 58 W/(m·K) |
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| Thermal expansion | 8.56 × 10⁻⁵ K⁻¹ |
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| Mohs hardness | 0.3 |
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| Young’s modulus | 2.4 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 | 7440-17-7 |
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| Latin name | Rubidium |
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| Discovered by | R. Bunsen, G. Kirchhoff · 1861 |
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| Named by | --- |
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Natural isotopes
| Isotope | Mass (u) | Abundance |
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| 85Rb | 84.91179 | 72.17 % |
| 87Rb | 86.909181 | 27.83 % |
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