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Lanthanum

From Academic Kids

BariumLanthanumCerium
La
Ac  
 
 
Missing image
La-TableImage.png
image:La-TableImage.png


General
Name, Symbol, NumberLanthanum, La, 57
Chemical series Lanthanides
Group, Period, Block3 , 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 level2, 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
isoNAhalf-life DMDE MeVDP
137La{syn.}60,000 yrs e capture0.600137Ba
138La0.09%1.05×1011 yrse capture1.737138Ba
138La0.09%1.05×1011 yrsβ-1.044138Ce
139La99.91%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.

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Contents

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:
  • 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

External links

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