69TmThulium168.934218 u
Thulium (Tm)
Thulium is a lanthanide with atomic number 69, in period 6, in the f-block of the periodic table. Its atomic mass is 168.934218 u and its electron configuration is [Xe] 4f¹³ 6s². Solid at 25 °C.
Key facts
| Atomic number | 69 |
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| Atomic mass | 168.934218 u |
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| Category | Lanthanide |
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| Period | 6 |
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| Group | f-block, no group number |
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| Block | f |
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| Electron configuration | [Xe] 4f¹³ 6s² |
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| Electrons per shell | 2, 8, 18, 31, 8, 2 |
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| Electronegativity (Pauling) | 1.25 |
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| Oxidation states | +2, +3common in bold |
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| State at 25 °C | Solid |
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| Melting point | 1818 K1544.85 °C |
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| Boiling point | 2223 K1949.85 °C |
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| Density | 9.32 g/cm³ |
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Atomic properties
| First ionization energy | 6.184 eV |
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| Electron affinity | 50 kJ/mol |
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| Atomic radius | 177 pm |
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| Covalent radius | 190 pm |
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| Van der Waals radius | 227 pm |
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| Common ions | Tm³⁺ |
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| Protons, neutrons, electrons | 69, 100, 69 |
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Physical and thermal properties
| Molar volume | 19.13 cm³/mol |
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| Heat of fusion | 16.8 kJ/mol |
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| Heat of vaporization | 250 kJ/mol |
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| Specific heat | 160 J/(kg·K) |
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| Thermal conductivity | 17 W/(m·K) |
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| Thermal expansion | 1.33 × 10⁻⁵ K⁻¹ |
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| Mohs hardness | 1.77 |
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| Young’s modulus | 74 GPa |
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| Crystal structure | Simple hexagonal |
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| Magnetic type | Paramagnetic |
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Identification and history
| CAS number | 7440-30-4 |
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| Latin name | Thulium |
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| Discovered by | Per Teodor Cleve · 1879 |
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| Named by | --- |
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Natural isotopes
| Isotope | Mass (u) | Abundance |
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| 169Tm | 168.934219 | 100 % |
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