Quick Facts
| Property | Value |
|---|---|
| Symbol | La |
| Atomic Number | 57 |
| Atomic Mass | 138.91 u |
| Category | Lanthanide |
| Period | 6 |
| Group | 3 |
| Block | f |
| Electron Configuration | [Xe] 5d¹ 6s² |
Physical Properties
| Property | Value |
|---|---|
| State at 20°C | Solid |
| Density | 6.162 g/cm³ |
| Melting Point | 920°C (1193 K) |
| Boiling Point | 3464°C (3737 K) |
| Appearance | Silvery-white, soft metal |
Atomic Properties
| Property | Value |
|---|---|
| Electron Configuration | [Xe] 5d¹ 6s² |
| Electronegativity | 1.10 (Pauling scale) |
| First Ionization Energy | 538.1 kJ/mol |
| Atomic Radius | 187 pm |
| Covalent Radius | 207 pm |
| Van der Waals Radius | 240 pm |
History and Discovery
Discovered by: Carl Gustaf Mosander Year of Discovery: 1839 Location: Stockholm, Sweden
Etymology
Named from the Greek "lanthanein" meaning "to lie hidden" or "to escape notice," because it was hidden in cerium oxide.
Discovery Story
Carl Gustaf Mosander discovered lanthanum in 1839 by carefully decomposing cerium nitrate. He found that cerium oxide contained a new element that had previously escaped detection. Mosander continued and later discovered didymium (which was itself later separated into praseodymium and neodymium).
Isotopes
| Isotope | Natural Abundance | Half-life | Decay Mode |
|---|---|---|---|
| ¹³⁸La | 0.089% | 1.02 × 10¹¹ years | β⁺, β⁻ |
| ¹³⁹La | 99.911% | Stable | - |
Occurrence
Natural Abundance
Lanthanum comprises about 39 ppm of Earth's crust, more abundant than lead. It is found in monazite and bastnasite ores along with other rare earth elements. China produces about 60% of the world's rare earth elements.
Extraction and Production
- Solvent Extraction: From rare earth concentrates
- Ion Exchange: For separation from other lanthanides
- Sources: Monazite and bastnasite mining
- Part of total rare earth production (~200,000 tons/year)
Applications and Uses
Catalysts
- Fluid catalytic cracking (FCC) in petroleum refining
- Automotive catalytic converters
- Chemical synthesis catalysts
Optics
- Camera and telescope lenses (lanthanum glass)
- High-refractive-index glass
- Night vision equipment
Batteries
- Nickel-metal hydride batteries (lanthanum alloys)
- Hybrid vehicle batteries
Other Uses
- Lighter flints (mischmetal containing lanthanum)
- Carbon arc lamp electrodes
- Hydrogen storage alloys
- Pool water treatment
Biological Role
Lanthanum has no known biological role.
In the Human Body
Lanthanum is not normally found in the body. It has low toxicity.
Medical Uses
Lanthanum carbonate (Fosrenol) is used to treat high phosphate levels in kidney disease patients.
Safety and Hazards
Toxicity
Lanthanum has low to moderate toxicity. Rare earth elements may accumulate in the body.
Handling Precautions
- Metal can ignite if finely divided
- Handle with care in powder form
- Store in inert atmosphere
- Standard rare earth handling procedures
Environmental Impact
Rare earth mining has significant environmental impacts, including radioactive waste from thorium. China's processing has caused notable pollution.
Interesting Facts
- Lanthanum gives its name to the lanthanide series of elements
- Despite being a "rare earth," lanthanum is more common than lead
- Lanthanum glass provides excellent optical properties for camera lenses
- It was hidden in cerium for nearly 40 years before discovery
- Lanthanum is essential for high-performance catalysts in oil refining