57LaLanthanum138.90547 u
Lanthanum (La)
Lanthanum is a lanthanide with atomic number 57, in period 6, in the f-block of the periodic table. Its atomic mass is 138.90547 u and its electron configuration is [Xe] 5d¹ 6s². Solid at 25 °C.
Key facts
| Atomic number | 57 |
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| Atomic mass | 138.90547 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] 5d¹ 6s² |
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| Electrons per shell | 2, 8, 18, 18, 9, 2 |
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| Electronegativity (Pauling) | 1.1 |
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| Oxidation states | +1, +2, +3common in bold |
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| State at 25 °C | Solid |
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| Melting point | 1193 K919.85 °C |
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| Boiling point | 3737 K3463.85 °C |
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| Density | 6.146 g/cm³ |
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Atomic properties
| First ionization energy | 5.577 eV |
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| Electron affinity | 48 kJ/mol |
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| Atomic radius | 187 pm |
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| Covalent radius | 207 pm |
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| Van der Waals radius | 240 pm |
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| Common ions | La³⁺ |
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| Protons, neutrons, electrons | 57, 82, 57 |
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Physical and thermal properties
| Molar volume | 22.39 cm³/mol |
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| Heat of fusion | 6.3 kJ/mol |
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| Heat of vaporization | 400 kJ/mol |
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| Specific heat | 195 J/(kg·K) |
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| Thermal conductivity | 13 W/(m·K) |
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| Thermal expansion | 1.21 × 10⁻⁵ K⁻¹ |
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| Mohs hardness | 2.5 |
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| Young’s modulus | 37 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 | 7439-91-0 |
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| Latin name | Lanthanum |
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| Discovered by | Carl Gustaf Mosander · 1839 |
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| Named by | --- |
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Natural isotopes
| Isotope | Mass (u) | Abundance |
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| 138La | 137.907124 | 0.08881 % |
| 139La | 138.906363 | 99.91119 % |
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