Lanthanum

57 barium ← lanthanum → cerium - ↑ La ↓ Ac periodic table
General
Name, Symbol, Number	lanthanum, La, 57
Chemical series	lanthanides
Group, Period, Block	3, 6, f
Appearance	silvery white
Atomic mass	138.90547(7) g/mol
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/cm³
Liquid density at m.p.	5.94 g/cm³
Melting point	1193 K (920 °C, 1688 °F)
Boiling point	3737 K (3464 °C, 6267 °F)
Heat of fusion	6.20 kJ/mol
Heat of vaporization	402.1 kJ/mol
Heat capacity	(25 °C) 27.11 J/(mol·K)
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 (Pauling scale)
Ionization energies (more)	1st: 538.1 kJ/mol
	2nd: 1067 kJ/mol
	3rd: 1850.3 kJ/mol
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·K)
Thermal expansion	(r.t.) (α, poly) 12.1 µm/(m·K)
Speed of sound (thin rod)	(20 °C) 2475 m/s
Speed of sound (thin rod)	(r.t.) (α form) 36.6 m/s
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
Notable 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

Lanthanum (chemical symbol La, atomic number 57) is a soft, silvery white metallic element. Found in combination with other rare earth elements, it is the most reactive of the rare-earth metals.

Occurrence

Lanthanum.

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.

Monazite ((Ce, La, Th, Nd, Y)PO₄ and bastnasite ((Ce, La, Y)CO₃F) are principal ores in which lanthanum occurs in percentages up to 25 to 38 percent.

Etymology and history

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

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.

Notable characteristics

Lanthanum belongs to period 6 and group 3 of the periodic table. It is often considered as the first of the lanthanides, which are a group of "inner transition metals". From the standpoint of their electronic structure, the lanthanides are characterized by the gradual filling of the 4f subshell. Lanthanum, however, has no electrons in its 4f subshell, and it best fits with the elements of group 3.

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.

Isotopes

Naturally occurring lanthanum consists of one stable isotope (¹³⁹La) and one radioactive (¹³⁸La) isotope, with the stable isotope, ¹³⁹La, being the most abundant (99.91% natural abundance). Many 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. All 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.

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

Applications

• Carbon lighting applications, especially by the motion picture industry for studio lighting and projection.
• Lanthanum oxide (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.
• 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 under Biological role.)
• Lanthanum nitrate is mainly applied in specialty glass, water treatment and catalyst.
• Cerium-activated lanthanum bromide is the recent inorganic scintillator that has a combination of high light yield and the best energy resolution.

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.

Precautions

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

See also

• Chemical element
• Metal
• Periodic table
• Inner transition metal

References

ISBN links support NWE through referral fees

• Lanthanum Los Alamos National Laboratory. Retrieved December 24, 2006.
• Greenwood, N.N.; and Earnshaw, A. (1998). Chemistry of the Elements (2nd Edition). Oxford, U.K.; Burlington, Massachusetts: Butterworth-Heinemann, Elsevier Science. ISBN 0750633654. Online version available at [1].
• Chang, Raymond (2006). Chemistry (ninth ed.) New York: McGraw-Hill Science/Engineering/Math. ISBN 0073221031.
• Cotton, F. Albert; and Wilkinson, Geoffrey (1980). Advanced Inorganic Chemistry (4th ed.), New York: Wiley. ISBN 0-471-02775-8.

External links

• WebElements.com – Lanthanum

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