Lanthanum (La)
Stable isotopes of lanthanum available from ISOFLEX
| Isotope | Z(p) | N(n) | Atomic Mass | Natural Abundance | Enrichment Level | Chemical Form |
| La-138 | 57 | 81 | 137.90711 | 0.09% | 5.90% | Oxide |
| La-139 | 57 | 82 | 138.906349 | 99.91% | 99.99% | Oxide |
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Lanthanum was discovered in 1839 by Carl Gustaf Mosander. Its name derives from the Greek word lanthanein, meaning “to lie hidden.”
Lanthanum is a white, malleable, soft, ductile metal with a hexagonal close-pack crystal system that transforms to face-centered cubic crystals at 310 ºC, further transforming to a body-centered cubic allotropic modification at 868 ºC. It oxidizes rapidly in air and corrodes in moist air. It is soluble in acids and decomposes in water to lanthanum hydroxide and hydrogen. Combustion in air or oxygen produces lanthanum sesquioxide. Lanthanum reacts vigorously when heated with halogens above 200 ºC, forming lanthanum halides. It combines with nitrogen, carbon, sulfur and phosphorus at elevated temperatures, forming binary salts. With metalloid elements such as boron, silicon, selenium and arsenic, similar reactions occur at high temperatures, forming similar binary compounds. In nature, lanthanum never occurs in its free state; it is always found associated with other rare-earth metals.
As a pure metal, lanthanum has limited uses except for research purposes; however, in alloy form, it has several metallurgical applications. When alloyed with iron, chromium, nickel or molybdenum, it improves resistance of these metals to oxidation. It also improves the impact strength, fluidity, ductility and other mechanical properties of the alloys.
In its powdered form, lanthanum ignites spontaneously. Exposure to lanthanum may delay blood clotting and cause liver injury.
Properties of Lanthanum
| Name | Lanthanum |
| Symbol | La |
| Atomic number | 57 |
| Atomic weight | 138.91 |
| Standard state | Solid at 298 °K |
| CAS Registry ID | 7439-91-0 |
| Group in periodic table | N/A |
| Group name | Lanthanoid |
| Period in periodic table | 6 |
| Block in periodic table | f-block |
| Color | Silvery white |
| Classification | Metallic |
| Melting point | 918 °C |
| Boiling point | 3457 °C |
| Vaporization point | 3464 ºC |
| Thermal conductivity | 13.4 W/(m·K) at 298.2 °K |
| Electrical resistivity | 5.70 µΩ·cm at 25 °C |
| Electronegativity | 1.17 |
| Specific heat | 0.19 J/(g·K) |
| Heat of vaporization | 400 kJ·mol-1 at 3457 °C |
| Heat of fusion | 6.2 kJ·mol-1 |
| Density of liquid | 5.94 g/cm3 at 918 °C |
| Density of solid | 6.166 g/cm3 |
| Electron configuration | [Xe]5d16s2 |
| Atomic radius | 1.879 Å |
| Ionic radius | La3+: 1.061 Å |
| Oxidation state | +3 |
