Lanthanum

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57 barium ← lanthanum → cerium - ↑ La ↓ Ac Periodic Table - Extended Periodic Table
General
Name, Symbol, Number	lanthanum, La, 57
Chemical series	lanthanides
Group, Period, Block	3, 6, f
Appearance	silvery white
Standard atomic weight	138.90547(7)  g·mol−1
Electron configuration	[Xe] 5d1 6s2
Electrons per shell	2, 8, 18, 18, 9, 2
Physical properties
Phase	solid
Density (near r.t.)	6.162  g·cm−3
Liquid density at m.p.	5.94  g·cm−3
Melting point	1193 K (920 °C, 1688 °F)
Boiling point	3737 K (3464 °C, 6267 °F)
Heat of fusion	6.20  kJ·mol−1
Heat of vaporization	402.1  kJ·mol−1
Heat capacity	(25 °C) 27.11  J·mol−1·K−1
Vapor pressure (extrapolated) P(Pa) 1 10 100 1 k 10 k 100 k at T(K) 2005 2208 2458 2772 3178 3726
Atomic properties
Crystal structure	hexagonal
Oxidation states	3 (strongly basic oxide)
Electronegativity	1.10 (scale Pauling)
Ionization energies (more)	1st:  538.1  kJ·mol−1
	2nd:  1067  kJ·mol−1
	3rd:  1850.3  kJ·mol−1
Atomic radius	195  pm
Covalent radius	169  pm
Miscellaneous
Magnetic ordering	?
Electrical resistivity	(r.t.) (α, poly) 615 nΩ·m
Thermal conductivity	(300 K) 13.4  W·m−1·K−1
Thermal expansion	(r.t.) (α, poly) 12.1 µm/(m·K)
Speed of sound (thin rod)	(20 °C) 2475 m/s
Young's modulus	(α form) 36.6  GPa
Shear modulus	(α form) 14.3  GPa
Bulk modulus	(α form) 27.9  GPa
Poisson ratio	(α form) 0.280
Mohs hardness	2.5
Vickers hardness	491  MPa
Brinell hardness	363  MPa
CAS registry number	7439-91-0
Selected isotopes
Main article: Isotopes of lanthanum iso NA half-life DM DE (MeV) DP 137La syn 60,000 yrs ε 0.600 137Ba 138La 0.09% 105×109yrs ε 1.737 138Ba β- 1.044 138Ce 139La 99.91% La is stable with 82 neutrons
References

Lanthanum (IPA: /ˈlanθənəm/) is a chemical element in the periodic table that has the symbol La and atomic number 57.

Contents 1 Notable characteristics 2 Applications 3 History 4 Biological Role 5 Occurrence 6 Isotopes 7 Precautions 8 References 9 See Also 10 External links

[edit] Notable characteristics

Lanthanum is a silvery white metallic element belonging to group 3 of the periodic table and is a lanthanide. Found in some rare-earth minerals, usually in combination with cerium and other rare earth elements. Lanthanum is malleable, ductile, and soft enough to be cut with a knife. It is one of the most reactive of the rare-earth metals. The metal reacts directly with elemental carbon, nitrogen, boron, selenium, silicon, phosphorus, sulfur, and with halogens. It oxidizes rapidly when exposed to air. Cold water attacks lanthanum slowly, while hot water attacks it much more rapidly.

[edit] Applications

Uses of lanthanum:

• Carbon lighting applications, especially by the motion picture industry for studio lighting and projection.
• La₂O₃ improves the alkali resistance of glass, and is used in making special optical glasses, such as:
  • Infrared absorbing glass.
  • Camera and telescope lenses, because of the high refractive index and low dispersion of rare-earth glasses.
• Small amounts of lanthanum added to steel improves its malleability, resistance to impact and ductility.
• Small amounts of lanthanum added to iron helps to produce nodular cast iron.
• Small amounts of lanthanum added to molybdenum decreases the hardness of this metal and its sensitivity to temperature variations.
• Small amounts of lanthanum are present in many pool products to remove the phosphates that feed algae.
• Mischmetal, a pyrophoric alloy used e.g. in lighter flints, contains 25% to 45% lanthanum.
• Lanthanum oxide and the boride are used in electronic vacuum tubes as hot cathode materials with strong emissivity of electrons. Crystals of LaB₆ are used in high brightness, extended life, thermionic electron emission sources for scanning electron microscopes.
• in Gas tungsten arc welding electrodes, as a substitute for radioactive thorium.
• 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.
• Petroleum cracking catalysts.
• Gas lantern mantles.
• Glass and lapidary polishing compound.
• La-Ba age dating of rocks and ores.
• Lanthanum carbonate is used medically as a phosphate binder for the treatment of hyperphosphatemia. See details below under Biological Role.
• Lanthanum nitrate is mainly applied in specialty glass, water treatment and catalyst.
• Cerium activated Lanthanum bromide is the recent inorganic scintillator which has a combination of high light yield and the best energy resolution.
• Like horseradish peroxidase, lanthanum is used as an electron-dense tracer in molecular biology^[1].

[edit] History

Lanthanum was discovered in 1839 by Swedish chemist Carl Gustav Mosander, when he partially decomposed a sample of cerium nitrate by heating and treating the resulting salt with dilute nitric acid. From the resulting solution, he isolated a new rare earth he called lantana. Lanthanum was isolated in relatively pure form in 1923.

The word lanthanum comes from the Greek λανθανω [lanthanō] = to lie hidden.

Lanthanum is the most strongly basic of all the trivalent lanthanides, and this property is what allowed Mosander to isolate and purify the salts of this element. Basicity separation as operated commercially involved the fractional precipitation of the weaker bases (such as "didymium") from nitrate solution by the addition of magnesium oxide or dilute ammmonia gas. Purified lanthanum remained in solution. (The basicity methods were only suitable for lanthanum purification; "didymium" could not be efficiently further separated in this manner.) The alternative technique of fractional crystallization was invented by Dimitry Mendeleev himself, in the form of the double ammonium nitrate tetrahydrate, which he used to separate the less-soluble lanthanum from the more-soluble "didymium" in the 1870's. This system would be used commercially in lanthanum purification until the development of practical solvent extraction methods that started in the late 1950's. (A detailed process using the double ammonium nitrates to provide 4N pure lanthanum, neodymium concentrates and praseodymium concentrates is presented in Callow 1967, at a time when the process was just becoming obsolete.) As operated for lanthanum purification, the double ammonium nitrates were recrystallized from water. When later adapted by Carl Auer won Welsbach for the splitting of "didymium", nitric acid was used as solvent to lower the solubility of the system. Lanthanum is relatively easy to purify, since it has only one adjacent lanthanide, cerium, which itself is very readily removed due to its potential tetravalency.

[edit] Biological Role

Lanthanum has no known biological role. The element is not absorbed orally, and when injected its elimination is very slow. Lanthanum carbonate was approved as a medication (Fosrenol®, Shire Pharmaceuticals) to absorb excess phosphate in cases of end-stage renal failure. Some rare-earth chlorides, such as lanthanum chloride (LaCl₃), are known to have anticoagulant properties.

While Lanthanum has pharmacological effects on several receptors and ion channels its specificity for the GABA receptor is unique among divalent cations. Lanthanum acts at the same modulatory site on the GABAR 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.

[edit] Occurrence

Although lanthanum belongs to chemical elements group called rare earth metals, it is not rare at all. Lanthanum is available in relatively large quantities (32 ppm in Earth’s crust). "Rare earths" got their name since they were indeed rare as compared to the "common" earths such as lime or magnesia, and historically only a few deposits were known.

Monazite (Ce, La, Th, Nd, Y)PO₄, and bastnasite (Ce, La, Y)CO₃F, are the principal ores in which lanthanum occurs, in percentages of up to 25 to 38 percent of the total lanthanide content. Lanthanum is more generally enriched in bastnasite as opposed to monazite, in commercial orebodies. Until 1949, bastnasite was a rare and obscure mineral, not even remotely contemplated as a potential commercial source for lanthanides. In that year, the vast deposit at Mountain Pass California was discovered. This discovery alerted geologists as to the existence of a whole new class of rare earth deposit, the rare-earth bearing carbonatite, other examples of which soon surfaced, particularly in Africa and China.

See also category:Lanthanide minerals

[edit] Isotopes

Main article: isotopes of lanthanum

Naturally occurring 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 105×10⁹ 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 that are less than 1 minute. This element also has 3 meta states.

The isotopes of lanthanum range in atomic weight from 117 u (¹¹⁷La) to 155 u (¹⁵⁵La).

[edit] Precautions

Lanthanum has a low to moderate level of toxicity, and should be handled with care. In animals, the injection of lanthanum solutions produces glycaemia, low blood pressure, degeneration of the spleen and hepatic alterations.