Lanthanum (La)
Lanthanide
Lanthanum opens the lanthanide series — the “rare earths” that are not actually rare, just difficult to separate. It sharpens camera lenses, stores hydrogen in NiMH battery alloys, and helps crack crude oil into petrol.
Position on the periodic table
Atomic properties
| Atomic number | 57 |
|---|---|
| Atomic mass | 138.905 amu |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 5d1 |
| Noble gas shorthand | [Xe] 5d16s2 |
| Electrons per shell | 2, 8, 18, 18, 9, 2 |
| Valence electrons (outer shell) | 2 |
| Common oxidation states | +3 |
| Electronegativity (Pauling) | 1.1 |
| Covalent radius (approx.) | 207 pm |
| First ionization energy | 538.1 kJ/mol |
| Electron affinity | 53 kJ/mol |
Physical properties
| State at 25 °C | Solid |
|---|---|
| Density | 6.162 g/cm³ |
| Melting point | 919.85 °C (1193 K) |
| Boiling point | 3463.8 °C (3737 K) |
| Appearance | silvery white |
| Radioactive | No |
| Origin | Occurs naturally |
Electron configuration of lanthanum
Lanthanum's ground-state electron configuration is 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 5d1, usually shortened to [Xe] 5d16s2. Its electrons occupy 6 shells (2, 8, 18, 18, 9, 2), placing it in period 6 of the f-block. Explore it interactively in the electron configuration calculator.
Uses of lanthanum
- NiMH battery alloys
- High-refraction optical glass
- Petroleum cracking catalysts
- Studio carbon-arc lighting
Biological role: None known.
Occurrence: Obtained from monazite and bastnäsite ores.
Common compounds of lanthanum
La2O3
Lanthanum oxide
LaNi5
Lanthanum-nickel hydrogen-storage alloy
History and discovery
Discovered: 1839 — Carl Gustaf Mosander. Name origin: From Greek lanthanein, “to lie hidden” — it hid inside cerium ore for years.
Carl Gustaf Mosander teased lanthanum out of cerium nitrate in 1839.
Safety notes
Low-to-moderate toxicity; mainly an occupational dust concern.
Educational context only — always follow your school's laboratory rules and never handle chemicals without proper supervision. See our disclaimer.
Practice questions
Quick practice: Lanthanum
1. What is the chemical symbol of Lanthanum?
2. What is the atomic number of Lanthanum?
3. Which category does Lanthanum belong to?
4. What is the state of Lanthanum at room temperature?
5. Which period of the periodic table is Lanthanum in?
Lanthanum FAQs
What is the atomic number of lanthanum?
Lanthanum's atomic number is 57 — every lanthanum atom has 57 protons in its nucleus.
What is the symbol for lanthanum?
La. From Greek lanthanein, “to lie hidden” — it hid inside cerium ore for years.
Is lanthanum a metal, nonmetal, or metalloid?
Lanthanum is classified as a lanthanide.
What state is lanthanum at room temperature?
At about 25 °C, lanthanum is a solid. It melts at 919.85 °C.
What is lanthanum used for?
Key uses include: nimh battery alloys; high-refraction optical glass; petroleum cracking catalysts.
Related elements
Keep working with this element
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