LANTHANUM
TRANSITION ELEMENT: SCANDIUM GROUP
| Atomic number: | 57 |
| Group numbers: | 3 |
| Period: | 6 |
| Electronic configuration: | [Xe] 5d1 6s2 |
| Formal oxidation number: | +3 |
| Electronegativities: | 1.1 |
| Atomic radius / pm: | 187 |
| Relative atomic mass: | 138.905 47(7) |
Lanthanum was discovered by Carl Gustaf Mosander (SE) in 1839. The origin of the name comes from the Greek word lanthanein meaning to lie hidden. It is a soft, silvery-white, malleable, ductile metal that tarnishes readily in air and reacts with oxidants. Reaction with water releases hydrogen gas, metal ignites and burns readily. Lanthanum is found with rare earths in monazite and bastnasite. Monazite sand typical contains 25% lanthanum. It is used in the electrodes of high-intensity, carbon-arc lights. Because it gives glass refractive properties, it is used in expensive camera lenses. The price of 99.9 % pure lanthanum pieces is 232.50 € for 100 g.
| Density / g dm-3: | 6145 | (298 K) |
| Molar volume / cm3mol-1: | 22.60 | (298 K) |
| Electrical resistivity / µΩcm: | 57 | (20 °C) |
| Thermal conductivity / W m-1K-1: | 13.5 |
| Melting point / °C: | 918 |
| Boiling point / °C: | 3464 |
| Heat of fusion / kJ mol-1: | 10.04 |
| Heat of vaporization / kJ mol-1: | 402.1 |
| Heat of atomization / kJ mol-1: | 431.29 |
| First ionization energy / kJ mol-1: | 538.10 |
| Second ionization energy / kJ mol-1: | 1067.14 |
| Third ionization energy / kJ mol-1: | 1850.34 |
| in the atmosphere / ppm: | - |
| in the Earth's crust / ppm: | 16 |
| in the oceans / ppm: | 0.0003 |
| Crystal structure: | hexagonal |
| Unit-cell dimensions / pm: | a=377.0, c=121.59 |
| Space group: | P63/mmc |
| Isotope | Relative atomic mass | Mass percent (%) |
|---|---|---|
| 138La | 137.907107(4) | 0.0902(2) |
| 139La | 138.906348(3) | 99.9098(2) |
| Balanced half-reaction | Eo / V | |
|---|---|---|
| La3+ + 3e- → La(s) | - 2.52 | |
| La(OH)3(s) + 3e- → La(s) + 3OH- | - 2.90 |
Citing this page:
Generalic, Eni. "Lanthanum." EniG. Periodic Table of the Elements. KTF-Split, 18 Jan. 2024. Web. {Date of access}. <https://www.periodni.com/la.html>.
