Instruct: Given a question, retrieve passages that can help answer the question.
Query: What is lanthanum named for?
Lanthanum usually occurs together with cerium and the other rare earth elements. Lanthanum was first found by the Swedish chemist Carl Gustav Mosander in 1839 as an impurity in cerium nitrate – hence the name lanthanum, from the Ancient Greek λανθάνειν (lanthanein), meaning "to lie hidden". Although it is classified as a rare earth element, lanthanum is the 28th most abundant element in the Earth's crust, almost three times as abundant as lead. In minerals such as monazite and bastnäsite, lanthanum composes about a quarter of the lanthanide content.[5] It is extracted from those minerals by a process of such complexity that pure lanthanum metal was not isolated until 1923.
Lanthanum is a chemical element with symbol La and atomic number 57. It is a soft, ductile, silvery-white metal that tarnishes rapidly when exposed to air and is soft enough to be cut with a knife. It is the eponym of the lanthanide series, a group of 15 similar elements between lanthanum and lutetium in the periodic table, of which lanthanum is the first and the prototype. It is also sometimes considered the first element of the 6th-period transition metals, which would put it in group 3, although lutetium is sometimes placed in this position instead. Lanthanum is traditionally counted among the rare earth elements. The usual oxidation state is +3. Lanthanum has no biological role in humans but is essential to some bacteria. It is not particularly toxic to humans but does show some antimicrobial activity.
Lanthanum trifluoride is a refractory ionic compound of lanthanum and fluorine.
Lanthanum hydroxide does not react much with alkaline substances, however is slightly soluble in acidic solution. In temperatures above 330 °C it decays into Lanthanum peroxide, LaOOH, which, upon further heating, decomposes into Lanthanum oxide.
As expected from periodic trends, lanthanum has the largest atomic radius of the lanthanides and the stable group 3 elements. Hence, it is the most reactive among them, tarnishing slowly in air and burning readily to form lanthanum(III) oxide, La2O3, which is almost as basic as calcium oxide.[15] A centimeter-sized sample of lanthanum will corrode completely in a year as its oxide spalls off like iron rust, instead of forming a protective oxide coating like aluminium and lanthanum's lighter congeners scandium and yttrium.[16] Lanthanum reacts with the halogens at room temperature to form the trihalides, and upon warming will form binary compounds with the nonmetals nitrogen, carbon, sulfur, phosphorus, boron, selenium, silicon and arsenic.[8][9] Lanthanum reacts slowly with water to form lanthanum(III) hydroxide, La(OH)3.[17] In dilute sulfuric acid, lanthanum readily forms the aquated tripositive ion [La(H2O)9]3+: this is colorless in aqueous solution since La3+ has no f electrons.[17] Lanthanum is the strongest and hardest base among the lanthanides and group 3 elements, which is again expected from its being the largest of them.[18]
Lanthanum strontium cobalt ferrite (LSCF), also called lanthanum strontium cobaltite ferrite is a specific ceramic oxide derived from lanthanum cobaltite of the ferrite group. It is a phase containing lanthanum(III) oxide, strontium oxide, cobalt oxide and iron oxide (cobalt iron oxide).
They are called lanthanides because the elements in the series are chemically similar to lanthanum. Both lanthanum and lutetium have been labeled as group 3 elements, because they have a single valence electron in the 5d shell. However, both elements are often included in discussions of the chemistry of lanthanide elements. Lanthanum is the more often omitted of the two, because its placement as a group 3 element is somewhat more common in texts and for semantic reasons: since "lanthanide" means "like lanthanum", it has been argued that lanthanum cannot logically be a lanthanide, but IUPAC acknowledges its inclusion based on common usage.[6]
Lanthanum(III) bromide (LaBr) is an inorganic halide salt of lanthanum. When pure, it is a colorless white powder. The single crystals of LaBr are hexagonal crystals with melting point of 783 °C. It is highly hygroscopic and water-soluble. There are several hydrates, LaBr·x HO, of the salt also known. It is often used as a source of lanthanum in chemical synthesis and as a scintillation material in certain applications.
While lanthanum has pharmacological effects on several receptors and ion channels, its specificity for the GABA receptor is unique among trivalent cations. Lanthanum acts at the same modulatory site on the GABA receptor as zinc, a known negative allosteric modulator. The lanthanum cation La3+ is a positive allosteric modulator at native and recombinant GABA receptors, increasing open channel time and decreasing desensitization in a subunit configuration dependent manner.[53]
Lanthanum hexaboride (LaB, also called lanthanum boride and LaB) is an inorganic chemical, a boride of lanthanum. It is a refractory ceramic material that has a melting point of 2210 °C, and is insoluble in water and hydrochloric acid. It has a low work function and one of the highest electron emissivities known, and is stable in vacuum. Stoichiometric samples are colored intense purple-violet, while boron-rich ones (above LaB) are blue. Ion bombardment changes its color from purple to emerald green.
Among the lanthanides, lanthanum is exceptional as it does not have any 4f electrons; indeed, the sudden contraction and lowering of energy of the 4f orbital that is important for the chemistry of the lanthanides only begins to happen at cerium. Thus it is only very weakly paramagnetic, unlike the strongly paramagnetic later lanthanides (with the exceptions of the last two, ytterbium and lutetium, where the 4f shell is completely full).[10] Furthermore, since the melting points of the trivalent lanthanides are related to the extent of hybridisation of the 6s, 5d, and 4f electrons, lanthanum has the second-lowest (after cerium) melting point among all the lanthanides: 920°C.[11] The lanthanides become harder as the series is traversed: as expected, lanthanum is a soft metal. Lanthanum has a relatively high resistivity of 615nΩm at room temperature; in comparison, the value for the good conductor aluminium is only 26.50nΩm.[12][13] Lanthanum is the least volatile of the lanthanides.[14] Like most of the lanthanides, lanthanum has a hexagonal crystal structure at room temperature. At 310°C, lanthanum changes to a face-centered cubic structure, and at 865°C, it changes to a body-centered cubic structure.[13]
Lanthanum carbonate, La(CO), is the salt formed by lanthanum(III) cations and carbonate anions. It is an ore of lanthanum metal, (Bastnäsite) along with monazite.
The process was improved again, to allow repeated separation of lanthanum from the barium solution, as the lanthanum built up. Initially, a phosphate process was used, where lanthanum was precipitated as lanthanum phosphate. This was later abandoned when an oxalate or hydroxide method was developed; lanthanum was precipitated as lanthanum hydroxide and then converted to a filterable precipitate by addition of oxalate with a trace of fluoride. The oxalate method had to be performed quickly, as the oxalate ion was susceptible to radiolysis and the lanthanum had the tendency to go back into solution. The oxalate process could be performed by remotely operated devices. The batches contained about of radiolanthanum, the highest radiation levels people had ever worked with at that time. Special tools had to be developed for remote handling of the hot materials. Lead bricks were used for shielding the sources. The radiation dose limit for the personnel was set to 500 mrem (5 mSv) per source preparation. Sometimes this limit was exceeded; once the received dose was 2 rem (20 mSv).
Lanthanum usually occurs together with cerium and the other rare earth elements. Lanthanum was first found by the Swedish chemist Carl Gustav Mosander in 1839 as an impurity in cerium nitrate – hence the name "lanthanum", from the Ancient Greek "λανθάνειν" ("lanthanein"), meaning "to lie hidden". Although it is classified as a rare earth element, lanthanum is the 28th most abundant element in the Earth's crust, almost three times as abundant as lead. In minerals such as monazite and bastnäsite, lanthanum composes about a quarter of the lanthanide content. It is extracted from those minerals by a process of such complexity that pure lanthanum metal was not isolated until 1923.
It has a perovskite-based crystal structure, which has the general form ABO. In the crystal, the 'A' sites are occupied by lanthanum and strontium atoms, and the 'B' sites are occupied by the smaller manganese atoms. In other words, the material consists of lanthanum manganite with some of the lanthanum atoms substitutionally doped with strontium atoms. The strontium (valence 2+) doping on lanthanum (valence 3+) introduces extra holes in the valence band and thus increases electronic conductivity.
However, when lanthanum carbonate is used for treating hyperphosphatemia, its side effects, namely Myalgia, muscular cramping, and Peripheral edema, should be clinically monitored.
In the "crossover" step, the lanthanum fluoride process was used. Lanthanum salts and hydrogen fluoride were added again and lanthanum fluoride was precipitated, while hexavalent plutonium was left in solution. This removed lanthanides like cerium, strontium and lanthanum, that bismuth phosphate could not. The plutonium was again reduced with oxalic acid and the lanthanum fluoride process was repeated. This time potassium hydroxide was added to metathesize the solution. Liquid was removed with a centrifuge and the solid dissolved in nitric acid to form plutonium nitrate. At this point, a batch sent would have been concentrated to .
Lanthanum ytterbium oxide is a solid inorganic compound of lanthanum, ytterbium and oxygen with the chemical formula of LaYbO. This compound adopts the Perovskite structure.
The name "didymium" continued to be used in the rare earth metal industry. In the US, commercial "didymium" salts were what remained after cerium had been removed from the natural products obtained from monazite, and thus it contained lanthanum, as well as Mosander's "didymium". A typical composition might have been 46% lanthanum, 34% neodymium, and 11% praseodymium, with the remainder mostly being samarium and gadolinium for material extracted from South African "rock monazite" from Steenkampskraal.
Lanthanum is the first element and prototype of the lanthanide series.[lower-alpha 1] In the periodic table, it appears to the right of the alkaline earth metal barium and to the left of the lanthanide cerium. Lanthanum is often considered to be a group 3 element, along with its lighter congeners scandium and yttrium and its heavier congener, the radioactive actinium,[7] although this classification is sometimes disputed. Similarly to scandium, yttrium, and actinium, the 57 electrons of a lanthanum atom are arranged in the configuration [Xe]5d16s2, with three valence electrons outside the noble gas core. In chemical reactions, lanthanum almost always gives up these three valence electrons from the 5d and 6s subshells to form the +3 oxidation state, achieving the stable configuration of the preceding noble gas xenon.[8] Some lanthanum(II) compounds are also known, but they are much less stable.[9]
Lanthanum is the third-most abundant of all the lanthanides, making up 39mg/kg of the Earth's crust, behind neodymium at 41.5mg/kg and cerium at 66.5mg/kg. It is almost three times as abundant as lead in the Earth's crust.[29] Despite being among the so-called "rare earth metals", lanthanum is thus not rare at all, but it is historically so named because it is rarer than "common earths" such as lime and magnesia, and historically only a few deposits were known. Lanthanum is considered a rare earth metal because the process to mine it is difficult, time-consuming, and expensive.[9] Lanthanum is rarely the dominant lanthanide found in the rare earth minerals, and in their chemical formulae it is usually preceded by cerium. Rare examples of La-dominant minerals are monazite-(La) and lanthanite-(La).[30]
Lanthanum hydroxide can be obtained by adding an alkali such as ammonia to aqueous solutions of lanthanum salts such as lanthanum nitrate. This produces a gel-like precipitate that can then be dried in air. 
Lanthanum carbonate is used as a starting material in lanthanum chemistry, particularly in forming mixed oxides, for example
Hydrogen sponge alloys can contain lanthanum. These alloys are capable of storing up to 400 times their own volume of hydrogen gas in a reversible adsorption process. Heat energy is released every time they do so; therefore these alloys have possibilities in energy conservation systems.[13][38] Mischmetal, a pyrophoric alloy used in lighter flints, contains 25% to 45% lanthanum.[39] Lanthanum oxide and the boride are used in electronic vacuum tubes as hot cathode materials with strong emissivity of electrons. Crystals of LaB 6 are used in high-brightness, extended-life, thermionic electron emission sources for electron microscopes and Hall-effect thrusters.[40] Lanthanum trifluoride (LaF 3) is an essential component of a heavy fluoride glass named ZBLAN. This glass has superior transmittance in the infrared range and is therefore used for fiber-optical communication systems.[41] Cerium-doped lanthanum bromide and lanthanum chloride are the recent inorganic scintillators, which have a combination of high light yield, best energy resolution, and fast response. Their high yield converts into superior energy resolution; moreover, the light output is very stable and quite high over a very wide range of temperatures, making it particularly attractive for high-temperature applications. These scintillators are already widely used commercially in detectors of neutrons or gamma rays.[42] Carbon arc lamps use a mixture of rare earth elements to improve the light quality. This application, especially by the motion picture industry for studio lighting and projection, consumed about 25% of the rare-earth compounds produced until the phase out of carbon arc lamps.[13][43] Lanthanum(III) oxide (La 2O 3) improves the alkali resistance of glass and is used in making special optical glasses, such as infrared-absorbing glass, as well as camera and telescope lenses, because of the high refractive index and low dispersion of rare-earth glasses.[13] Lanthanum oxide is also used as a grain-growth additive during the liquid-phase sintering of silicon nitride and zirconium diboride.[44] Small amounts of lanthanum added to steel improves its malleability, resistance to impact, and ductility, whereas addition of lanthanum to molybdenum decreases its hardness and sensitivity to temperature variations.[13] Small amounts of lanthanum are present in many pool products to remove the phosphates that feed algae.[45] Lanthanum oxide additive to tungsten is used in gas tungsten arc welding electrodes, as a substitute for radioactive thorium.[46][47] Various compounds of lanthanum and other rare-earth elements (oxides, chlorides, etc.) are components of various catalysis, such as petroleum cracking catalysts.[48] Lanthanum-barium radiometric dating is used to estimate age of rocks and ores, though the technique has limited popularity.[49] Lanthanum carbonate was approved as a medication (Fosrenol, Shire Pharmaceuticals) to absorb excess phosphate in cases of end-stage renal failure.[50] Lanthanum fluoride is used in phosphor lamp coatings. Mixed with europium fluoride, it is also applied in the crystal membrane of fluoride ion-selective electrodes.[9] Like horseradish peroxidase, lanthanum is used as an electron-dense tracer in molecular biology.[51] Lanthanum-modified bentonite (or phoslock) is used to remove phosphates from water in lake treatments.[52]
Lanthanum manganite is an electrical insulator and an A-type antiferromagnet. It is the parent compound of several important alloys, often termed rare-earth manganites or colossal magnetoresistance oxides. These families include lanthanum strontium manganite, lanthanum calcium manganite and others.