Lanthanum
Definition and meaning of Lanthanum in chemistry.
![Lanthanum element card: symbol La, atomic number 57, atomic mass 138.91, electron configuration [Xe] 5d¹ 6s², oxidation states +3, Lanthanide, group 3, period 6, solid at room temperature.](/assets/images/terms/lanthanum-chemical-element.webp)
Lanthanum is a soft, silvery-white metal with the symbol La and atomic number 57. It is the first element in the lanthanide series on the periodic table. The pure metal reacts quickly and loses its shine when exposed to air.
In more detail
Lanthanum sits in group 3 of the periodic table, where it starts the lanthanide series. This group contains fifteen elements that share very similar chemical properties. These elements sit in the f-block at the bottom of the periodic table.
Lanthanum is highly reactive, so it tarnishes rapidly in normal room air. This reaction forms a powdery white coating of lanthanum(III) oxide, which has the formula La2O3. The metal also reacts vigorously with hot water, releasing flammable hydrogen gas.
Miners extract lanthanum from complex minerals that contain phosphate, such as monazite. These mineral ores usually contain lanthanum bonded tightly with another metal called cerium. Because these metals are so similar, separating them requires complex chemical processes.
When lanthanum reacts with other elements, it almost always loses three outer electrons. This loss of electrons creates a very stable +3 oxidation state. A common student misconception is that rare earth elements are very rare.
Lanthanum is actually quite common and exists in greater amounts than lead. Chemical companies use lanthanum compounds as catalysts to speed up chemical reactions. For instance, oil refineries use them to crack heavy crude oil into gasoline.
Engineers also add lanthanum to other metals to make them stronger and easier to shape. For example, it is a key ingredient in mischmetal, which makes lighter flints.
Key facts
| Field | General Chemistry |
|---|---|
| Symbol | La |
| Atomic number | 57 |
| Atomic mass | 138.91 u |
| Category | Lanthanide |
| Melting point | 920 °C |
Lanthanum is a key component in rechargeable nickel-metal hydride batteries. These batteries power many hybrid electric cars on the road today. The metal forms a special alloy that stores hydrogen atoms very well. This lets the battery to hold a large amount of energy safely.
Frequently asked questions
Why does lanthanum lose its shine so quickly in air?
Lanthanum reacts rapidly with oxygen gas in the surrounding air. This reaction creates a white oxide layer that covers the metal surface.
What makes lanthanum useful in battery technology?
It forms a metal alloy that can absorb and release hydrogen atoms. This ability is essential for the chemistry of nickel-metal hydride batteries.
Is lanthanum actually rare in the Earth's crust?
No, lanthanum is not rare, despite being called a rare earth metal. It is more common in the Earth's crust than lead.
Related terms
Sources & references
See our sources and editorial standards.