Lanthanum

Barium – Lanthanum – Cerium La Ac       Missing image La-TableImage.png image:La-TableImage.png Full table
General
Name, Symbol, Number	Lanthanum, La, 57
Chemical series	Lanthanides
Group, Period, Block	3 , 6, f
Density, Hardness	6146 kg/m3, 2.5
Appearance	silvery white Missing image La,57.jpg
Atomic properties
Atomic weight	138.9055 u
Atomic radius (calc.)	195 (n/a) pm
Covalent radius	169 pm
van der Waals radius	n/a pm
Electron configuration	[Xe]5d16s2
e- 's per energy level	2, 8,18,18, 9, 2
Oxidation states (Oxide)	3 (strong base)
Crystal structure	hexagonal
Physical properties
State of matter	solid (_)
Melting point	1193 K (1688 ?F)
Boiling point	3730 K (6255 ?F)
Molar volume	22.39 ×10-6 m3/mol
Heat of vaporization	414 kJ/mol
Heat of fusion	6.2 kJ/mol
Vapor pressure	1.33E-07 Pa at 1193 K
Velocity of sound	2475 m/s at 293.15 K
Miscellaneous
Electronegativity	1.1 (Pauling scale)
Specific heat capacity	190 J/(kg*K)
Electrical conductivity	1.26 106/m ohm
Thermal conductivity	13.5 W/(m*K)
1st ionization potential	538.1 kJ/mol
2nd ionization potential	1067 kJ/mol
3rd ionization potential	1850.3 kJ/mol
4th ionization potential	4819 kJ/mol
Most stable isotopes
iso NA half-life DM DE MeV DP 137La {syn.} 60,000 yrs e capture 0.600 137Ba 138La 0.09% 1.05×1011 yrs e capture 1.737 138Ba 138La 0.09% 1.05×1011 yrs β- 1.044 138Ce 139La 99.91% La is stable with 82 neutrons
SI units & STP are used except where noted.

Lanthanum 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 External links

Notable characteristics

Lanthanum is a silvery white metallic element belonging to group 3 of the periodic table and often considered to be one of the lanthanides. 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.

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.
• Mischmetal, a pyrophoric alloy used e.g. in lighter flints, contains 25% to 45% lanthanum.
• The oxide and the boride are used in electronic vacuum tubes.
• 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 Nitrate is mainly applied in specialty glass, water treatment and catalyst.

History

Lanthanum was discovered in 1839 by Carl 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 lanthanein, to lie hidden.

Biological role

Lanthanum has no known biological role.

The element is not absorbed orally, and when injected its elimination is very slow. Lanthanum carbonate is being studied as a compound 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.

Occurrence

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 percent and 38 percent respectively.

Isotopes

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 1.05×10¹¹ 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. This element also has 3 meta states.

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

Precautions

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

References

• Los Alamos National Laboratory – Lanthanum (http://periodic.lanl.gov/elements/57.html)

External links

• WebElements.com – Lanthanum (http://www.webelements.com/webelements/elements/text/La/index.html)
• EnvironmentalChemistry.com – Lanthanum (http://environmentalchemistry.com/yogi/periodic/La.html)