90ThThorium232.0377 u
Thorium (Th)
Thorium is an actinide with atomic number 90, in period 7, in the f-block of the periodic table. Its atomic mass is 232.0377 u and its electron configuration is [Rn] 6d² 7s². Solid at 25 °C.
Key facts
| Atomic number | 90 |
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| Atomic mass | 232.0377 u |
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| Category | Actinide |
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| Period | 7 |
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| Group | f-block, no group number |
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| Block | f |
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| Electron configuration | [Rn] 6d² 7s² |
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| Electrons per shell | 2, 8, 18, 32, 18, 10, 2 |
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| Electronegativity (Pauling) | 1.3 |
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| Oxidation states | +1, +2, +3, +4common in bold |
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| State at 25 °C | Solid |
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| Melting point | 2023 K1749.85 °C |
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| Boiling point | 5061 K4787.85 °C |
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| Density | 11.7 g/cm³ |
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Atomic properties
| First ionization energy | 6.307 eV |
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| Electron affinity | --- |
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| Atomic radius | 180 pm |
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| Covalent radius | 206 pm |
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| Van der Waals radius | 237 pm |
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| Common ions | Th_{4+} |
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| Protons, neutrons, electrons | 90, 142, 90 |
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Physical and thermal properties
| Molar volume | 19.8 cm³/mol |
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| Heat of fusion | 16 kJ/mol |
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| Heat of vaporization | 530 kJ/mol |
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| Specific heat | 118 J/(kg·K) |
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| Thermal conductivity | 54 W/(m·K) |
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| Thermal expansion | 1.1 × 10⁻⁵ K⁻¹ |
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| Mohs hardness | 3 |
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| Young’s modulus | 79 GPa |
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| Crystal structure | Face-centered cubic |
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| Magnetic type | Paramagnetic |
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Identification and history
| CAS number | 7440-29-1 |
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| Latin name | Thorium |
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| Discovered by | Jöns Jakob Berzelius · 1829 |
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| Named by | --- |
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Natural isotopes
| Isotope | Mass (u) | Abundance |
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| 230Th | 230.033132 | 0.02 % |
| 232Th | 232.038054 | 99.98 % |
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