Lanthanum (symbol La) is a chemical element with atomic number 57. It is a soft, ductile, silvery-white metal that belongs to the group of elements known as the lanthanides or rare-earth elements. Here are some detailed points about lanthanum:
Discovery and Naming
- Carl Gustav Mosander first isolated lanthanum in 1839 from a sample of cerium nitrate, which he obtained from the mineral cerite. Initially, he called it "lanthanum" after the Greek word "lanthanein," which means "to lie hidden," due to its elusive nature.
Physical Properties
- Atomic Weight: 138.90547
- Melting Point: 920 °C (1193 K, 1688 °F)
- Boiling Point: 3464 °C (3737 K, 6267 °F)
- Density: 6.162 g/cm³ at 20 °C
- Lanthanum has a hexagonal crystal structure.
Chemical Properties
- Lanthanum reacts with oxygen when heated to form lanthanum oxide (La2O3).
- It also reacts with water to form lanthanum hydroxide and hydrogen gas.
- Lanthanum is known for its ability to reduce in aqueous solution, often used in the production of other rare-earth metals.
Uses
- Lanthanum compounds are used in the production of catalysts for petroleum refining, particularly in fluid catalytic cracking.
- It's a component in high-refractive-index glass, used in camera lenses, binoculars, and other optical instruments.
- Lanthanum is used in NiMH batteries, where it helps in increasing the energy density.
- The element is also utilized in lanthanum carbonate, a medication used to treat high levels of phosphate in patients with kidney disease.
Occurrence
- Lanthanum is never found as a free element in nature. It occurs in various minerals, most notably in monazite and bastnäsite, where it is associated with other rare-earth elements.
Isotopes
- Lanthanum has two naturally occurring isotopes: 139La (stable) and 138La, which is radioactive with a very long half-life (approximately 1.05×1011 years).
Environmental Impact
- There is no significant environmental impact from lanthanum itself, but the mining and processing of lanthanides can lead to environmental concerns due to the use of acids and other chemicals.
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