19KPotassium39.0983 u
Potassium (K)
Potassium is an alkali metal with atomic number 19, in period 4 and group 1 of the periodic table. Its atomic mass is 39.0983 u and its electron configuration is [Ar] 4s¹. Solid at 25 °C.
Key facts
| Atomic number | 19 |
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| Atomic mass | 39.0983 u |
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| Category | Alkali Metal |
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| Period | 4 |
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| Group | 1 |
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| Block | s |
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| Electron configuration | [Ar] 4s¹ |
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| Electrons per shell | 2, 8, 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 | 336.53 K63.38 °C |
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| Boiling point | 1032 K758.85 °C |
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| Density | 0.89 g/cm³ |
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Atomic properties
| First ionization energy | 4.341 eV |
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| Electron affinity | 48.4 kJ/mol |
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| Atomic radius | 235 pm |
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| Covalent radius | 203 pm |
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| Van der Waals radius | 275 pm |
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| Common ions | K⁺ |
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| Protons, neutrons, electrons | 19, 20, 19 |
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Physical and thermal properties
| Molar volume | 45.94 cm³/mol |
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| Heat of fusion | 2.33 kJ/mol |
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| Heat of vaporization | 76.9 kJ/mol |
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| Specific heat | 757 J/(kg·K) |
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| Thermal conductivity | 100 W/(m·K) |
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| Thermal expansion | 7.74 × 10⁻⁵ K⁻¹ |
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| Mohs hardness | 0.4 |
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| Young’s modulus | 3.53 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 | 7440-09-7 |
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| Latin name | Kalium |
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| Discovered by | Humphry Davy · 1807 |
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| Named by | --- |
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Natural isotopes
| Isotope | Mass (u) | Abundance |
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| 39K | 38.963706 | 93.2581 % |
| 40K | 39.963998 | 0.0117 % |
| 41K | 40.961825 | 6.7302 % |
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