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Lanthanum

physical science Maturity 7-9 Next article →

Lanthanum is a chemical element with the symbol La and atomic number 57. It is a soft, silvery-white metal that is quite ductile, meaning it can be easily shaped.

Mosander Carl Gustav bw
Mosander Carl Gustav bw

As the first element in the lanthanide series, it serves as the prototype for a group of 15 similar elements. While it is classified as a rare-earth element, it is not actually rare in the Earth's crust. It is the 28th most abundant element, making it nearly three times as common as lead. This element is vital for many technologies, ranging from specialized glass to medical treatments.

At the atomic level, lanthanum has a specific way of behaving during chemical reactions. A single lanthanum atom has 57 electrons arranged in a specific configuration. It has three valence electrons located in the 5d and 6s subshells. In most chemical reactions, the atom gives up these three electrons. This process creates a +3 oxidation state, which allows the atom to reach a stable configuration similar to the noble gas xenon. While some lanthanum(II) compounds exist, they are much less stable than the +3 state.

Lanthanum stable nucleus
Lanthanum stable nucleus

The physical properties of lanthanum are shaped by its unique electron structure. Unlike many other lanthanides, a single lanthanum atom in a gas phase has no 4f electrons. This makes it only weakly paramagnetic, which means it is not strongly attracted to magnetic fields. However, its 4f shell can become partially occupied in certain chemical environments. This allows the electrons to participate in chemical bonding. This characteristic is why lanthanum is placed in the f-block of the periodic table. It also has a relatively low melting point of 920 °C compared to other trivalent lanthanides.

Lanthanum is highly reactive, especially when it meets the air or water. It is the most reactive element among the lanthanide series. When exposed to air, it tarnishes quickly and can turn completely dark in just a few hours. If you had a sample only one centimeter in size, it could corrode entirely within a single year. This happens because the oxide that forms does not create a protective coating. Instead, it flakes off like rust on iron. When lanthanum reacts with water, it produces lanthanum(III) hydroxide and releases a lot of heat, often accompanied by a hissing sound.

The history of lanthanum is a story of uncovering what was hidden. In 1839, the Swedish chemist Carl Gustaf Mosander discovered the element. He was studying cerium nitrate and realized it was actually a mixture of different oxides. By roasting the sample in air and treating it with nitric acid, he separated the new oxides. He named the substance lanthana, which comes from the Greek word meaning "to lie hidden."

Mosander Carl Gustav bw
Mosander Carl Gustav bw

It took many more years of complex work to isolate the pure metal. Scientists did not successfully isolate pure lanthanum metal until 1923.

Extracting lanthanum is a difficult and expensive process because it is usually found mixed with other elements. It often occurs alongside cerium in minerals like monazite and bastnäsite.

Monazite acid cracking process
Monazite acid cracking process

In these minerals, lanthanum typically makes up about one-quarter of the total lanthanide content. Because the different rare-earth elements are so chemically similar, separating them requires very complex methods. This difficulty is part of why the term "rare-earth" is still used, even though the element is relatively abundant in the crust.

Today, lanthanum is used in a wide variety of important industrial and medical roles. It is used as a catalyst and as an additive in glass to change its properties. You might find it in carbon arc lamps for projectors or as an ignition element in lighters and torches.

LaB6HotCathode
LaB6HotCathode

It is also used in gas tungsten arc welding electrodes and as electron cathodes. In the field of medicine, lanthanum carbonate serves a critical purpose. It acts as a phosphate binder for patients experiencing kidney failure, helping to manage high phosphate levels in the blood.

Finally, we can look at the very building blocks of the element through its isotopes. Naturally occurring lanthanum is made of two isotopes: La-139 and La-135. The La-139 isotope is by far the most common, making up 99.911% of all natural lanthanum. It is created in stars through processes called the s-process and the r-process.

Lanthanum stable nucleus
Lanthanum stable nucleus

The other isotope, La-135, is a very rare primordial radioisotope. Most other versions of lanthanum are synthetic, meaning they are created by humans in a laboratory.

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🖼️ Images & Media (4)
File:Lanthanum stable nucleus.png
Lanthanum stable nucleus.png
File:Mosander Carl Gustav bw.jpg
Mosander Carl Gustav bw.jpg
File:Monazite acid cracking process.svg
Monazite acid cracking process.svg
File:LaB6HotCathode.jpg
LaB6HotCathode.jpg
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