Lanthanum (La)

Lanthanum (symbol La) is the chemical element with atomic number 57: a lanthanide (rare earth), solid at 0 °C, with an atomic mass of 138.91 u. Discovered in 1839 (Carl Gustaf Mosander).

Lanthanum opens the lanthanide series, fifteen metals with near-identical chemistry also known as the “rare earths.” Its name comes from the Greek lanthanein, “to lie hidden,” because it spent years concealed inside a cerium ore. You'll find it in hybrid-car batteries, high-end optical glass and the catalysts that refine crude oil.

Key facts

Atomic number: 57
Symbol: La
French name: Lanthane
Atomic mass: 138.91 u
Molar mass: 138.91 g/mol
Family: Lanthanides
Position: period 6, group 3, f-block
State at 0 °C: Solid
Melting point: 919.9 °C
Boiling point: 3,463.9 °C
Density: 6.16 g/cm³
Electronegativity (Pauling): 1.1
First ionization energy: 538 kJ/mol
Atomic radius: 195 pm
Electron configuration: [Xe] 5d¹ 6s²
Abundance in Earth's crust: 39 ppm (28th most abundant element)
Indicative price: 5 $/kg (order of magnitude)
Radioactive: no
Discovery: 1839, Carl Gustaf Mosander

Origin of the name

From the Greek lanthanein, “to lie hidden.”

What does lanthanum look like?

A silvery-white metal soft enough to cut with a knife. It tarnishes quickly in air, acquiring a whitish coat of oxide.

Where is lanthanum found?

At about 39 ppm (mg/kg) of Earth's crust, it is more abundant than lead: rare earths aren't really “rare,” just widely scattered. It always occurs mixed with the other lanthanides in a handful of ores such as monazite and bastnäsite. The giant Bayan Obo deposit in Inner Mongolia, China, holds an enormous share of them.

Natural sources

Bastnäsite
Monazite
Loparite

How is lanthanum produced?

The ore is crushed, concentrated and attacked with acid; the rare earths are then separated from one another by solvent extraction, a step repeated across hundreds of tanks in a row because their properties are so alike. The pure metal is made by electrolysis of molten salts or by reducing the fluoride with calcium.

Top producers

China
United States
Myanmar
Australia

What is lanthanum used for?

Electrodes in the nickel-metal hydride (NiMH) batteries of hybrid cars.
High-refractive-index optical glass for camera lenses and telescopes.
Cracking catalysts in oil refineries.
Lanthanum hexaboride cathodes in electron microscopes.
A drug (lanthanum carbonate) that traps phosphate in people with kidney failure.

In everyday life

The battery of a first-generation Toyota Prius
A DSLR camera lens
Lighter flint (“mischmetal” alloy)
Refined gasoline at the pump

Role in living things

Long thought to have no biological role, lanthanum turned out to be essential to certain methane-eating bacteria discovered in 2014 in an Italian volcanic crater: they use it in an enzyme that breaks down methanol. In humans it has no known function.

Hazards of lanthanum

Of low toxicity; its salts are even used as medicine. Fine powders can ignite spontaneously in air, and mining its ores generates waste containing radioactive thorium.

Cosmic origin

Dying stars: Made slowly in red giants (stars like the Sun at the end of their lives).
Neutron stars: Created when two neutron stars collide — the “forge” of gold.

History of lanthanum

In 1839 the Swedish chemist Carl Gustaf Mosander, a student of Berzelius, noticed that part of his “cerium” could be extracted separately: he had found a new element hiding inside it. Reasonably pure lanthanum metal wasn't obtained until 1923.

Did you know?

A first-generation Prius battery held roughly 10 to 15 kg of lanthanum.
Arc-lamp movie projectors used carbon electrodes doped with rare earths to produce an intense light close to sunlight.
Its name literally means “the hidden element.”

Isotopes of lanthanum

Natural lanthanum has just one stable isotope, lanthanum-139, plus a tiny pinch of lanthanum-138: radioactive, but decaying so slowly that it has survived since the Earth formed.

lanthanum-138: 0.089% of natural lanthanum, radioactive, half-life 1.03 × 10¹¹ years
lanthanum-139: 99.911% of natural lanthanum, stable
lanthanum-140: radioactive, half-life 1.68 days. A fission product monitored after nuclear accidents, once used as an industrial tracer.

Related elements

Same family (lanthanides): Cerium (Ce), Praseodymium (Pr), Neodymium (Nd), Promethium (Pm), Samarium (Sm), Europium (Eu), Gadolinium (Gd), Terbium (Tb), Dysprosium (Dy), Holmium (Ho), Erbium (Er), Thulium (Tm), Ytterbium (Yb), Lutetium (Lu).

Same column (group 3): Scandium (Sc), Yttrium (Y), Actinium (Ac).