|Name , symbol , atomic number||Lanthanum, La, 57|
|Element category||Transition metals|
|Group , period , block||3 , 6 , d|
|Mass fraction of the earth's envelope||17 ppm|
|Atomic mass||138.90547 (7) et al|
|Atomic radius||195 pm|
|Covalent radius||207 pm|
|Electron configuration||[ Xe ] 5 d 1 6 s 2|
|1. Ionization energy||5.5769 (6) eV ≈ 538.09 kJ / mol|
|2. Ionization energy||11.18496 (6) eV ≈ 1 079.18 kJ / mol|
|3. Ionization energy||19th.1773 (6) eV ≈ 1 850.33 kJ / mol|
|4. Ionization energy||49.95 (6) eV ≈ 4 820 kJ / mol|
|5. Ionization energy||61.6 (6) eV ≈ 5 940 kJ / mol|
|density||6.17 g / cm 3 (20 ° C )|
|magnetism||paramagnetic ( Χ m = 5.4 · 10 −5 )|
|Melting point||1193 K (920 ° C)|
|boiling point||3743 K (3470 ° C)|
|Molar volume||22.39 10 −6 m 3 mol −1|
|Heat of evaporation||400 kJ / mol|
|Heat of fusion||6.2 kJ mol −1|
|Speed of sound||2475 m · s −1|
|Electric conductivity||1.626 · 10 6 A · V −1 · m −1|
|Thermal conductivity||13 W m −1 K −1|
|Normal potential||−2.38 V (La 3+ + 3 e - → La)|
|Electronegativity||1.1 ( Pauling scale )|
|For other isotopes see list of isotopes|
As far as possible and customary, SI units are used.
Unless otherwise noted, the data given apply to standard conditions .
Lanthanum [ LANTAN (] ) is a chemical element with the element symbol La and atomic number 57. It is one of the transition metals and the rare earth metals in the periodic table it is in the sixth period and the third sub-group , or the 3rd IUPAC group or Scandium group . Usually it is also counted among the lanthanoids , even if the f-shell of the element is unoccupied.
In 1751, the Swedish mineralogist Axel Fredrik Cronstedt discovered a heavy mineral from the Bastnäs mine , later called Cerite . Thirty years later, fifteen-year-old Vilhelm Hisinger from the family who owned the mine sent a sample to Carl Scheele , who found no new elements in it. In 1803, after Hisinger became iron master, he and Jöns Jacob Berzelius returned to the mineral substance and isolated a new oxide , which they named Ceres Ceria after the dwarf planet discovered two years earlier. At the same time, ceria was isolated independently by Martin Heinrich Klaproth in Germany . Between 1839 and 1843, ceria was referred to as an oxide mixture by the Swedish surgeon and chemist Carl Gustav Mosander , who lived in the same house as Berzelius: He separated two other oxides, which he called lanthanum and didymia. He partially decomposed a sample of cerium nitrate by roasting it in the open air and then treating the resulting oxide with dilute nitric acid . Since the properties of lanthanum differed only slightly from those of cerium and were carried along in its salts, he called it from ancient Greek λανθάνειν [lanthanein] ("to be hidden"). The relatively pure lanthanum metal was first isolated in 1923.
Lanthanum occurs naturally only in chemical compounds associated with other lanthanides in various minerals. Mainly these are:
Extraction and presentation
After a laborious separation of the other lanthanum companions, the oxide is converted with hydrogen fluoride to lanthanum fluoride . This is then reduced to lanthanum with calcium to form calcium fluoride . The removal of remaining calcium residues and impurities takes place in an additional remelting process in a vacuum .
Lanthanum is ignoble. In the air it quickly becomes coated with a white oxide layer, which further reacts to form the hydroxide in moist air .
- Lanthanum reacts with the oxygen in the air to form lanthanum oxide , and with water further to lanthanum hydroxide .
At temperatures above 440 ° C , lanthanum burns to form lanthanum oxide (La 2 O 3 ). With the formation of hydrogen , a slow reaction takes place in cold water and a rapid reaction in warm water to form the hydroxide.
- Lanthanum in water creates lanthanum hydroxide and hydrogen.
Lanthanum dissolves in dilute acids with evolution of hydrogen.
It reacts directly with many elements in the warmth, with halogens even at room temperature. Lanthanum and hydrogen form a black, water-sensitive, non-stoichiometric hydride.
Lanthanum is a component in mischmetal . Pyrophoric flint materials contain 25 to 45 percent by weight of lanthanum. It is also used as a reducing agent in metallurgy. As a cast iron additive it supports the formation of spheroidal graphite , as an alloy additive it improves the oxidation resistance . Adding lanthanum reduces the hardness and temperature sensitivity of molybdenum .
High quality cathodes for generating free electrons are made of lanthanum hexaboride as a replacement for tungsten wire . High-purity lanthanum oxide is used in the glass industry to produce high-quality glasses with a high refractive index for optics, e.g. B. used for camera lenses.
As an alloy
- with cobalt :
The cobalt- lanthanum alloy LaCo 5 is used as a magnetic material, lanthanum-doped barium titanate for the production of PTC thermistors (temperature-dependent resistors). In connection with cobalt, iron , manganese , strontium and the like a. it serves as a cathode for high temperature fuel cells ( SOFC ). "Contaminated" lanthanum nickel (LaNi 5 ) is used as hydrogen storage in nickel-metal hydride accumulators . As an addition, it is used in carbon arc lamps for studio lighting and in film projection systems (historical use?).
- with titanium :
An alloy metal with a material composition of lanthanum and titanium is said to have the effect that the chip length is reduced during chip-forming processing. This is to facilitate the processing of the metal.
In the field of medicine, the alloy metal is used to produce corrosion-resistant and easily sterilizable instruments. This metal alloy with titanium should be particularly well suited for tools and apparatus for surgical interventions, since the allergy tendency when using such a metal alloy with titanium should be low in relation to other alloys.
As lanthanum oxide
- In optical glass , lanthanum oxide has a high refractive index and low dispersion . These glasses are used in optical devices such as cameras, telescopes or glasses.
- Lanthanum oxide replaces more toxic lead compounds in tableware such as wine glasses and in the glaze of porcelain. It also improves chemical resistance to alkalis . The dishes are "dishwasher safe".
- Addition of catalyst to zeolites in fluid catalytic cracking in the refinery for crude oil processing
- Manufacture of ceramic capacitor compounds and silicate-free glasses
- Part of glass polishing agents
- Manufacture of hot cathodes for electron tubes (also lanthanum borides)
As lanthanum carbonate
- Drug to lower the phosphate level in dialysis patients (so-called phosphate binders , precipitation as poorly soluble lanthanum phosphate )
Lanthanum is classified as having little toxicity. A toxic dose is currently unknown. However, lanthanum powder is considered to be highly corrosive because it is very easily damaged by e.g. B. Skin moisture reacts to form basic lanthanum hydroxide (similar to the elements calcium and strontium ). The lethal dose in rats is 720 mg.
In compounds, lanthanum can be present as colorless La 3+ .
- Lanthanum oxide La 2 O 3
- Lanthanum fluoride LaF 3
- Lanthanum chloride LaCl 3
- Lanthanum bromide LaBr 3
- Lanthaniodid Lal 3
- Lanthanum nitrate La (NO 3 ) 3
- Lanthanum sulfate La 2 (SO 4 ) 3
- Lanthanum carbonate La 2 (CO 3 ) 3
- Lanthanum hexaboride
- Lanthanum Oxide Fluoride LaOF
- Lanthanum sulfide fluoride LaSF
- Lanthanum sulfide chloride LaSCl
- Lanthanum fluoride carbonate LaF [CO 3 ]
- Lanthanum hydride (LaH 10 )
Superconductivity of the hydride
Lanthanum hydride (LaH 10 ) is a superconductor with the highest known transition temperature of 250 K (−23 ° C) at a pressure of around 170 gigapascals.
- Harry H. Binder: Lexicon of the chemical elements. S. Hirzel Verlag, Stuttgart 1999, ISBN 3-7776-0736-3 .
- The values for the properties (info box) are taken from www.webelements.com (Lanthanum) , unless otherwise stated .
- CIAAW, Standard Atomic Weights Revised 2013 .
- Entry on lanthanum in Kramida, A., Ralchenko, Yu., Reader, J. and NIST ASD Team (2019): NIST Atomic Spectra Database (ver. 5.7.1) . Ed .: NIST , Gaithersburg, MD. doi : 10.18434 / T4W30F ( https://physics.nist.gov/asd ). Retrieved June 11, 2020.
- Entry on lanthanum at WebElements, https://www.webelements.com , accessed on June 11, 2020.
- NN Greenwood, A. Earnshaw: Chemistry of the elements. 1st edition. VCH, Weinheim 1988, ISBN 3-527-26169-9 , p. 1219.
- Robert C. Weast (Ed.): CRC Handbook of Chemistry and Physics . CRC (Chemical Rubber Publishing Company), Boca Raton 1990, ISBN 0-8493-0470-9 , pp. E-129 to E-145. Values there are based on g / mol and given in cgs units. The value specified here is the SI value calculated from it, without a unit of measure.
- Yiming Zhang, Julian RG Evans, Shoufeng Yang: Corrected Values for Boiling Points and Enthalpies of Vaporization of Elements in Handbooks. In: Journal of Chemical & Engineering Data . 56, 2011, pp. 328-337, doi: 10.1021 / je1011086 .
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