Chemical Properties
solid
Physical properties
Lanthanum is a soft silvery-white metal that, when cut with a knife, forms an oxide withthe air (tarnishes) on the exposed area. It is the most reactive of the elements in the series. Itreacts slightly with cold water but rapidly with hot water, producing hydrogen gas (H2) andlanthanum oxide (La2O3). It directly interacts with several other elements, including nitrogen,boron, the halogens, carbon, sulfur, and phosphorus.
Its melting point is 918°C, its boiling point is 3,464°C, and its density is 6.15 g/cm3.
Isotopes
There are 49 isotopes of lanthanum. One, La-139, is stable and makes up99.910% of the known amount found on Earth. Another isotope has such a long halflifethat is considered stable: with a half-life of 1.05×10+11 years, La-138 makes up just0.090% of the known abundance on Earth. All the other isotopes are radioactive andhave half-lives ranging from 150 nanoseconds to several thousand years.
Origin of Name
From the Greek word lanthanein, meaning “to be hidden.”
Occurrence
The main ore in which lanthanum is found is monazite sands, and it is also found in themineral bastnasite. Monazite sands contain all of the rare-earth elements as well as some elementsthat are not rare-earths. Its ores are found in South Africa, Australia, Brazil, and Indiaand in California, Florida, and the Carolinas in the United States.
The prices of lanthanide elements are somewhat reasonable and are less than gold per kilogram.(Gold is about $1,800 per kg.) Cesium (Ce), which is relatively common, is often alloyedwith La, Nd, and Pr and iron to form misch metal. This alloy has several uses based on its uniqueability to spark when scratched. The most common use is as flints for cigarette lighters.
Lanthanum is the fourth most abundant of the rare-earths found on the Earth. Its abundanceis 18 ppm of the Earth’s crust, making it the 29th most abundant element on Earth. Itsabundance is about equal to the abundance of zinc, lead, and nickel, so it is not really rare.Because the chemical and physical properties of the elements of the lanthanide series are sosimilar, they are quite difficult to separate. Therefore, some of them are often used together asan alloy or in compounds.
Characteristics
Lanthanide, as a pure metal, is difficult to separate from its ores, and it is often mixed withother elements of the series. It is mostly obtained through an ion-exchange process from the sandsof the mineral monazite, which can contain as much as 25% lanthanum as well as the oxides ofseveral other elements of the series. The metal is malleable and ductile and can be formed intomany shapes. Lanthanum is considered the most basic (alkaline) of the rare-earth elements.
Definition
A soft ductile
malleable silvery metallic element that is
the first member of the lanthanoid series. It
is found associated with other lanthanoids
in many minerals, including monazite and
bastnaesite. Lanthanum is used in several
alloys (especially for lighter flints), as a catalyst,
and in making optical glass.
Symbol: La; m.p. 921°C; b.p. 3457°C;
r.d. 6.145 (25°C); p.n. 57; r.a.m.
138.9055.
Definition
lanthanum: Symbol La. A silverymetallic element belonging to group3 (formerly IIIA) of the periodic tableand often considered to be one of thelanthanoids; a.n. 57; r.a.m. 138.91;r.d. 6.146 (20°C); m.p. 921°C; b.p.3457°C. Its principal ore is bastnasite,from which it is separated by an ionexchangeprocess. There are two naturalisotopes, lanthanum–139 (stable)and lanthanum–138 (half-life1010–1015 years). The metal, being pyrophoric,is used in alloys for lighterflints and the oxide is used in someoptical glasses. The largest use of lanthanum,however, is as a catalyst incracking crude oil. Its chemistry resemblesthat of the lanthanoids. Theelement was discovered by CarlMosander (1797–1858) in 1839.
Purification Methods
It is a shiny metal that slowly tarnishes in air due to oxidation. It slowly decomposes by H2O in the cold and more rapidly on heating to form the hydroxide. The metal is cleaned by scraping off the tarnished areas until the shiny metal is revealed and stored under oil or paraffin. It burns in air at 450o. It exists in three forms: -form, -form and -form with transition temperatures of 310o and 864o, respectively. [Spedding et al. Ind Eng Chem 44 553 1952.]
Hazard
In powder form, lanthanum will ignite spontaneously. If ingested, it can cause liver damageand prevent blood from clotting. Many of its compounds are toxic.
Flammability and Explosibility
Flammable
Industrial uses
A chemical element, lanthanum, symbol La, thesecond most abundant element in the rare earthgroup, is a metal. The naturally occurring elementis made up of the isotopes and is one ofthe radioactive products of the fission of uranium,thorium, or plutonium. Lanthanum is themost basic of the rare earths and can be separatedrapidly from other members of the rareearth series by fractional crystallization. Considerablequantities of it are separated commercially,because it is an important ingredient inglass manufacture. Lanthanum imparts a highrefractive index to the glass and is used in themanufacture of expensive lenses. The metal isreadily attacked in air and is rapidly convertedto a white powder.
Lanthanum becomes a superconductorbelow about –267°C in both the hexagonal andface-centered crystal forms.
