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 one of the most reactive of the rare earth metals.

Contents

1 Occurrence
2 Etymology and history
3 Notable characteristics

3.1 Isotopes


4 Applications
5 Biological role and precautions
6 See also
7 References
8 External links
9 Credits



Lanthanum, its alloys, and its compounds have a wide range of applications. For instance, the element is used in motion-picture studio illumination that relies on carbon-arc lighting, and it is a substitute for thorium in gas tungsten-arc welding electrodes. It is an important component of mischmetal, a pyrophoric alloy used in lighter flints, and small amounts of this element may be added to steel to improve its malleability, or to molybdenum to decrease its hardness. Lanthanum oxide is useful for special optical glasses, such as camera and telescope lenses and infrared-absorbing glass. The oxide and boride are used in electronic vacuum tubes, and the carbonate has been approved for a medication that absorbs excess phosphate in end-stage cases of kidney failure.

Occurrence
 Lanthanum
Although lanthanum belongs to a group of chemical elements called the rare earth metals, it is not rare at all. It is available in relatively large quantities—32 parts per million (ppm) in the Earth’s crust.
The principal ores containing lanthanum are monazite ((Ce, La, Th, Nd, Y)PO4) and bastnasite ((Ce, La, Y)CO3F). The proportion of lanthanum in these ores can be as high as 25–38 percent. It usually occurs in combination with cerium and other rare earth elements.

Etymology and history
The word lanthanum comes from the Greek λανθανω [lanthanō], which means "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 resultant 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 six and group three (former group 3B) of the periodic table. It is often considered 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 three, corresponding to a group of transition metals.
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 percent 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 one minute. The isotopes of lanthanum range in atomic weight from 117 u (117La) to 155 u (155La).

Applications
Lanthanum is used for carbon-arc lighting applications, especially by the motion picture industry for studio lighting and projection.
In gas tungsten-arc welding electrodes, lanthanum is used as a substitute for radioactive thorium.
Small amounts of lanthanum added to steel improves its malleability, resistance to impact, and ductility.
Small amounts of lanthanum added to iron helps 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, for instance, in lighter flints, contains 25–45 percent lanthanum.
Hydrogen sponge alloys may contain lanthanum. These alloys are capable of storing up to 400 times their own volume of hydrogen gas in a reversible adsorption process.
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.
Lanthanum oxide and the boride (LaB6) 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.
Petroleum cracking catalysts.
Gas lantern mantles.
Glass and lapidary polishing compound.
Lanthanum-barium radiometric dating of rocks and ores.
Lanthanum carbonate is used medically as a phosphate binder for the treatment of a condition known as hyperphosphatemia. It has been approved as a medication (Fosrenol®, Shire Pharmaceuticals) to absorb excess phosphate in cases of end-stage renal failure.
Lanthanum nitrate is used mainly for specialty glasses, water treatment, and catalysis.
Cerium-activated lanthanum bromide is the recent inorganic scintillator that has a combination of high light yield and the best energy resolution.
Some rare-earth chlorides, such as lanthanum chloride (LaCl3), are known to have anticoagulant properties.
Biological role and precautions
Lanthanum has no known biological role. The element is not absorbed orally, and when injected into experimental animals, its elimination is very slow. It 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
Actinium
Chemical element
Metal
Periodic table
Inner transition metal
Transition metal
ReferencesISBN links support NWE through referral fees
Chang, Raymond. 2006. Chemistry, ninth ed. New York, NY: McGraw-Hill Science/Engineering/Math. ISBN 0073221031
Cotton, F. Albert, and Wilkinson, Geoffrey. 1980. Advanced Inorganic Chemistry, 4th ed. New York, NY: Wiley. ISBN 0-471-02775-8
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 Retrieved October 8, 2007.
Lanthanum Los Alamos National Laboratory. Retrieved October 8, 2007.
Jones, Adrian P., Frances Wall, and C. Terry Williams, eds. 1996. Rare Earth Minerals: Chemistry, Origin and Ore Deposits (The Mineralogical Society Series). London, UK: Chapman and Hall. ISBN 0412610302
External links
All links retrieved October 22, 2022.

Lanthanum WebElements.com.

Credits
New World Encyclopedia writers and editors rewrote and completed the Wikipedia article
in accordance with New World Encyclopedia standards. This article abides by terms of the Creative Commons CC-by-sa 3.0 License (CC-by-sa), which may be used and disseminated with proper attribution. Credit is due under the terms of this license that can reference both the New World Encyclopedia contributors and the selfless volunteer contributors of the Wikimedia Foundation. To cite this article click here for a list of acceptable citing formats.The history of earlier contributions by wikipedians is accessible to researchers here:

Lanthanum  history
The history of this article since it was imported to New World Encyclopedia:

History of "Lanthanum"
Note: Some restrictions may apply to use of individual images which are separately licensed.