Lanthanum
Element 57 · Lanthanide
Lanthanum is the first member of the lanthanide series and the element the whole row is named after. Like its neighbors, it is silvery, malleable, and reactive enough to tarnish in air and burn in oxygen. It almost always appears in the +3 oxidation state.
Its standout use is in optics: lanthanum oxide glass has a high refractive index with low dispersion, making it ideal for camera, telescope, and microscope lenses. Lanthanum also stores hydrogen in the nickel-metal hydride batteries of hybrid cars and sparks in the lighter flints made from misch metal.
Key facts
| Atomic number | 57 |
|---|---|
| Atomic weight | 138.91 |
| Category | Lanthanide |
| Group / Period | — / 6 |
| Block | f |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 5d1 |
| Common oxidation states | +3 |
| State at STP | Solid |
| Electronegativity | 1.10 |
| Density | 6.16 g/cm³ |
| Melting point | 920 °C |
| Boiling point | 3464 °C |
Occurrence
Lanthanum is found in the rare-earth minerals monazite and bastnasite, usually mixed with the other lanthanides. It is among the more abundant of the rare earth metals.
Applications
High-refractive-index glass for cameras and telescopes
Nickel-metal hydride rechargeable batteries
Lighter flints (misch metal alloy)
Hydrogen storage alloys
Common compounds
- lanthanum oxide
- lanthanum chloride
- lanthanum carbonate
- lanthanum hexaboride
Its name comes from the Greek lanthanein, meaning ‘to lie hidden’ — it hid inside cerium ore for decades before chemists isolated it in 1839.
Data source: IUPAC standard atomic weights 2021