Lanthanum
Lanthanum is a soft, silvery-white metallic element with atomic number 57. It is the first element in the lanthanide series.
Lanthanum oxide: Lanthanum oxide is an inorganic compound used in optical glass, ceramics, and catalysts. Its high refractive index makes it valuable in camera and telescope lenses.
Lanthanide: A lanthanide is an element in the series from lanthanum through lutetium, characterized by filling of the 4f subshell. Lanthanum is conventionally included as the series' first member, though its 4f shell is empty.
Carl Gustaf Mosander: Carl Gustaf Mosander was a Swedish chemist who discovered several rare-earth elements in the nineteenth century. He identified lanthanum in 1839 while investigating cerium compounds.
Lanthanum(III) ion: The lanthanum(III) ion is La³⁺, the most common oxidation state of lanthanum in compounds. Lanthanum readily loses three electrons, so its compounds are usually built around La³⁺.
Mischmetal: Mischmetal is an alloy of rare-earth elements, commonly used in lighter flints and metal alloys. Lanthanum can make up a substantial fraction of this alloy and helps form pyrophoric lighter flints.
Atomic number: Atomic number is the number of protons in an atom's nucleus and determines the element's identity. Lanthanum's 57 protons distinguish it from every other element.
Cerium: Cerium is a metallic chemical element with atomic number 58, immediately following lanthanum. Lanthanum was discovered as an impurity in material then believed to be pure cerium oxide.
Lanthanum hydroxide: Lanthanum hydroxide, La(OH)₃, is a sparingly soluble base formed from lanthanum(III) ions. It precipitates when alkaline solutions are added during lanthanum separation and purification.
Nickel–metal hydride battery: A nickel–metal hydride battery stores energy using a hydrogen-absorbing alloy at its negative electrode. Lanthanum-containing alloys absorb hydrogen in many nickel–metal hydride batteries.
Electron configuration: An electron configuration describes how electrons occupy an atom's shells, subshells, and orbitals. Lanthanum's configuration, [Xe] 5d¹ 6s², helps explain its chemistry and place among the lanthanides.