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57La138.91

Element 57, a lanthanide

Lanthanum

The first of the lanthanides, the row of look-alike metals that takes its name, and a working part of many hybrid car batteries.

At a glance

Symbol
La
Atomic number
57
Average atomic mass
138.91
Group
none; it sits in the lanthanide row below the table
Period
6
Family
lanthanide
Electron configuration
[Xe] 5d¹ 6s²
Electronegativity
1.10
Common ions
La³⁺

On the table

Periodic table with Lanthanum highlighted123456789101112131415161718123456757-7189-103HHeLiBeBCNOFNeNaMgAlSiPSClArKCaScTiVCrMnFeCoNiCuZnGaGeAsSeBrKrRbSrYZrNbMoTcRuRhPdAgCdInSnSbTeIXeCsBaLaCePrNdPmSmEuGdTbDyHoErTmYbLuHfTaWReOsIrPtAuHgTlPbBiPoAtRnFrRaAcThPaUNpPuAmCmBkCfEsFmMdNoLrRfDbSgBhHsMtDsRgCnNhFlMcLvTsOg

Period 6, in the lanthanide row set below the main table. The other lanthanides are tinted, and every cell opens its own article.

Electrons and bonding

Like the other lanthanides, it gives up three electrons to form the La³⁺ ion in most of its compounds.

Properties

State at 25 °C
solid
What it looks like
soft, silvery-white metal that tarnishes in air
Melting point
918 °C
Boiling point
3464 °C
Density
6.15 g/cm³

Where it is found

Found with the other rare earths in monazite and bastnäsite, mined mostly in China, the United States, Australia and Myanmar.

Discovery and name

Carl Gustaf Mosander found it in 1839 hidden in cerium nitrate, which he had thought was pure. He named it from the Greek lanthanein, to lie hidden.

What it is used for

Nickel-metal hydride batteries in hybrid cars contain kilograms of a lanthanum-rich alloy. Lanthanum oxide makes high-quality camera and telescope lenses, lanthanum catalysts crack crude oil into gasoline, and lanthanum carbonate is a medicine that controls phosphate levels in kidney patients.

In compounds

La₂O₃lanthanum oxide, in lens glassLaNi₅lanthanum nickel, stores hydrogenLa₂(CO₃)₃lanthanum carbonate, a medicineLaB₆lanthanum hexaboride, electron sources