Lanthanum
Atomic Data
| Atomic Number | 57 |
| Symbol | La |
| Atomic Weight | 138.91 u |
| Density (STP) | 6.162 g/cm³ |
| Melting Point | 919.85 °C (1193 K) |
| Boiling Point | 3463.85 °C (3737 K) |
| Electronegativity | 1.1 (Pauling) |
| Electron Config. | 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p6 5d1 6s2 |
| Oxidation States | +3 |
| Phase at STP | Solid |
| Category | Lanthanoid |
| Period / Group | 6 / None |
| CAS Number | 7439-91-0 |
Electron Configuration
[Xe] 5d1 6s2
| Shell | n | Subshell | Electrons | Cumulative |
|---|---|---|---|---|
| K | 1 | 1s | 2 | 2 |
| L | 2 | 2s | 2 | 4 |
| L | 2 | 2p | 6 | 10 |
| M | 3 | 3s | 2 | 12 |
| M | 3 | 3p | 6 | 18 |
| M | 3 | 3d | 10 | 28 |
| N | 4 | 4s | 2 | 30 |
| N | 4 | 4p | 6 | 36 |
| N | 4 | 4d | 10 | 46 |
| O | 5 | 5s | 2 | 48 |
| O | 5 | 5p | 6 | 54 |
| O | 5 | 5d | 1 | 55 |
| P | 6 | 6s | 2 | 57 |
| Total | 57 | 57 | ||
Isotopes of Lanthanum
Lanthanum has two naturally occurring stable isotopes. The most abundant is ¹³⁹La, comprising 99.91% of all naturally occurring Lanthanum.
| Isotope | Symbol | Protons | Neutrons | Abundance | Stability |
|---|---|---|---|---|---|
| Lanthanum-138 | ¹³⁸La | 57 | 81 | 0.09 | Stable |
| Lanthanum-139 | ¹³⁹La | 57 | 82 | 99.91 | Stable |
Abundance & Occurrence
Lanthanum is present in Earth's crust at approximately 39 ppm by mass and at approximately 2 ppm by mass throughout the universe.
Earth's Crust (ppm by mass)
Universe (ppm by mass)
Discovery & History
Read more about the discovery of the periodic table of elements →
Safety & Handling
- Dust inhalation: Lanthanum oxide and other lanthanum compound dusts are respiratory irritants; rare-earth pneumoconiosis has been documented in workers with heavy occupational exposure to mixed lanthanide dusts.
- Lanthanum chloride: Soluble lanthanum salts are moderately irritating to skin, eyes, and the gastrointestinal tract; they should be handled with gloves and eye protection, and ingestion avoided.
- Fire hazard: Lanthanum metal powder is flammable; metal fires require dry sand or Class D extinguishing agents.
- General precautions: Lanthanum has low acute toxicity in its common forms; inhalation of dusts is the primary hazard, and standard metal handling controls apply.
Lanthanum in the Real World
Real-World Uses
- Nickel-metal hydride batteries: The LaNi₅ hydrogen storage alloy reversibly absorbs and releases hydrogen and is the standard negative electrode material in NiMH rechargeable batteries used in hybrid vehicles and consumer electronics.
- High-refractive-index optical glass: Lanthanum oxide is added to specialty optical glasses to achieve high refractive indices (n > 1.8) with low dispersion, enabling compact camera lenses, binoculars, and microscope objectives with reduced chromatic aberration.
- Petroleum fluid catalytic cracking: Lanthanum-exchanged zeolite (LaY) catalysts are mixed into FCC catalyst formulations in oil refineries to improve catalytic activity, selectivity, and thermal stability during gasoline production from heavy crude fractions.
- Carbon arc lighting: Lanthanum and other rare-earth oxides are mixed into carbon arc electrodes to intensify and whiten arc emission, used in cinema projectors, searchlights, and theatrical lighting.
- Phosphors for fluorescent lighting: Lanthanum phosphate and lanthanum-doped aluminate phosphors contribute to blue and UV emission bands in tri-colour fluorescent lamp phosphor blends, improving colour rendering and efficiency.
Downloadable Resources
Free periodic table reference sheets for classrooms, study sessions, and laboratory use.
Frequently Asked Questions
What is lanthanum used for?
Lanthanum is used in high-refractive-index optical glass for camera lenses and microscopes, in nickel-metal hydride (NiMH) battery anodes (lanthanum-rich mischmetal alloys store hydrogen), and in fluid cracking catalysts used in oil refining. Lanthanum oxide is used in speciality ceramics. Lanthanum compounds are also used as phosphors in fluorescent lighting.
Is lanthanum rare?
Despite being called a 'rare earth element', lanthanum is actually quite abundant in Earth's crust: about 39 parts per million, comparable to cobalt. The 'rare' designation reflects historic difficulty in separating rare earths from each other, not true scarcity. However, lanthanum is not concentrated in easily mined deposits and most production comes from a few mines, primarily in China.
How was lanthanum discovered?
Lanthanum was discovered in 1839 by Swedish chemist Carl Gustaf Mosander. He found it as an impurity in cerium oxide (ceria), which had been isolated from the mineral cerite. Mosander separated a new oxide he called lanthana from ceria by treating it with dilute nitric acid. The name comes from the Greek 'lanthanein', meaning to lie hidden: reflecting how it had been concealed within cerium compounds.
What is mischmetal and why does it contain lanthanum?
Mischmetal is an unseparated alloy of rare-earth metals typically containing about 50% cerium, 25% lanthanum, 18% neodymium, and 7% other rare earths. It is produced directly from rare-earth ores without the expensive individual separation step. Mischmetal is used as a hydrogen-absorbing anode material in NiMH batteries (one of the largest lanthanum uses), as a pyrophoric material in lighter flints, and as an alloying addition to steel and magnesium alloys.