Lanthanum

Lanthanum is a chemical element with the symbol La and atomic number 57. Lanthanum is a silvery white metallic element that belongs to group 3 of the periodic table and is a lanthanide. It is found in some rare-earth minerals, usually in combination with cerium and other rare earth elements. Lanthanum is a malleable, ductile, and soft metal that oxidizes rapidly when exposed to air. It is produced from the minerals monazite and bastnäsite using a complex multistage extraction process. Lanthanum compounds have numerous applications as catalysts, additives in glass, carbon lighting and projection, ignition elements in lighters and torches, electron cathodes, scintillators, and others. Lanthanum carbonate (La2(CO3)3) was approved as a medication against renal failure.

Characteristics

Lanthanum is a soft, malleable and has hexagonal crystal structure at room temperature. At 310 °C, lanthanum changes to a face-centered cubic structure, and at 865 °C into a body-centered cubic structure. Lanthanum easily oxidizes (a centimeter-sized sample will completely oxidize within a year) and is therefore used as in elemental form only for research purposes. For example, single La atoms have been isolated by implanting them into fullerene molecules. If carbon nanotubes are filled with those lanthanum-encapsulated fullerenes and annealed, metallic nanochains of lanthanum are produced inside carbon nanotubes.

Lanthanum exhibits two oxidation states, +3 and +2, the former being much more stable. For example, LaH3 is more stable than LaH2. Lanthanum burns readily at 150 °C to form lanthanum(III) oxide: However, when exposed to moist air at room temperature, it forms a hydrated oxide with a large volume increase. Lanthanum is quite electropositive and reacts slowly with cold water and quite quickly with hot water to form lanthanum hydroxide: Lanthanum metal reacts with all the halogens. The reaction is vigorous if conducted at above 200 °C: Lanthanum dissolves readily in dilute sulphuric acid to form solutions containing the La(III) ions, which exist as [La(OH2)9]3+ complexes: Lanthanum combines with nitrogen, carbon, sulphur, phosphorus, boron, selenium, silicon and arsenic at elevated temperatures, forming binary compounds. Naturring lanthanum is composed of one stable (139La) and one radioactive (138La) isotope, with the stable isotope, 139La, being the most abundant (99.91% natural abundance). 38 radioisotopes have been characterized with the most stable being 138La with a half-life of 1.05×1011 years, and 137La with a half-life of 60,000 years. Most of the remaining radioactive isotopes have half-lives that are less than 24 hours, and the majority of these have half-lives less than 1 minute. This element also has three meta states. The isotopes of lanthanum range in atomic weight from 117 u (117La) to 155 u (155La).

Value

The base value of each unit of ranges between 5 and 20Ð per unit, with up to 2 units being found at any one time.

Presence on Mars: Very Rare