# Lanthanum

properties
[ Xe ] 5 d 1 6 s 2
57 La
General
Name , symbol , atomic number Lanthanum, La, 57
Element category Transition metals
Group , period , block 3 , 6 , d
Appearance silvery white
CAS number 7439-91-0
EC number 231-099-0
ECHA InfoCard 100.028.272
Mass fraction of the earth's envelope 17 ppm
Atomic
Atomic mass 138.90547 (7) et al
Electron configuration [ Xe ] 5 d 1 6 s 2
1. Ionization energy 5.5769 (6) eV538.09 kJ / mol
2. Ionization energy 11.18496 (6) eV1 079.18 kJ / mol
3. Ionization energy 19th.1773 (6) eV1 850.33 kJ / mol
4. Ionization energy 49.95 (6) eV4 820 kJ / mol
5. Ionization energy 61.6 (6) eV5 940 kJ / mol
Physically
Physical state firmly
Modifications 3
Crystal structure hexagonal
density 6.17 g / cm 3 (20 ° C )
Mohs hardness 2.5
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
Chemically
Oxidation states 3
Normal potential −2.38 V (La 3+ + 3 e - → La)
Electronegativity 1.1 ( Pauling scale )
Isotopes
isotope NH t 1/2 ZA ZE (M eV ) ZP
135 La {syn.} 19.5 h ε 1,200 135 Ba
136 La {syn.} 9.87 min ε 2.870 136 Ba
137 La {syn.} 60,000 a ε 0.600 137 Ba
138 La 0.09% 1.05 x 10 11 a ε 1.737 138 Ba
β - 1.044 138 Ce
139 La 99.91  % Stable
140 La {syn.} 1.6731 d β - 3,762 140 Ce
141 La {syn.} 3.92 h β - 2.502 141 Ce
For other isotopes see list of isotopes
NMR properties
Spin
quantum
number I
γ in
rad · T −1 · s −1
E r  ( 1 H) f L at
B = 4.7 T
in MHz
138 La 5 3.557 · 10 7 0.00008 13.19
139 La 7/2 3.808 · 10 7 0.0605 14.13
safety instructions
GHS labeling of hazardous substances

powder

danger

H and P phrases H: 260
EUH: 014
P: 223-231 + 232-370 + 378-422
As far as possible and customary, SI units are used.
Unless otherwise noted, the data given apply to standard conditions .

Lanthanum [ LANTAN (] listen ? / I ) 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.

## history

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.

## Occurrence

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 .

## properties

Lanthanum

### Physical Properties

The shiny silver-white metal is malleable and plastically deformable ( ductile ). There are three metallic modifications .

### Chemical properties

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 .

${\ displaystyle \ mathrm {2 \, La + 1.5 \, O_ {2} \ rightarrow \, La_ {2} O_ {3} \ _ {\ overrightarrow {\ mathrm {3 \, H_ {2} O} }} \ 2 \, La (OH) _ {3}}}$
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.

${\ displaystyle \ mathrm {2 \, La + 6 \, H_ {2} O \ rightarrow 2 \, La (OH) _ {3} +3 \, H_ {2}}}$
Lanthanum in water creates lanthanum hydroxide and hydrogen.

Lanthanum dissolves in dilute acids with evolution of hydrogen.

${\ displaystyle \ mathrm {2 \, La + 3 \, H_ {2} SO_ {4} \ rightarrow La_ {2} (SO_ {4}) _ {3} +3 \, H_ {2}}}$
Lanthanum and sulfuric acid react to form lanthanum sulfate and 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.

${\ displaystyle \ mathrm {La + n \, H_ {2} \ rightarrow LaH_ {2n}; 1

## use

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

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?).

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)

## safety instructions

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+ .

### 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.

Commons : Lanthanum  - collection of images, videos and audio files
Wiktionary: Lanthanum  - explanations of meanings, word origins, synonyms, translations

## Individual evidence

1. ^ Harry H. Binder: Lexicon of the chemical elements. S. Hirzel Verlag, Stuttgart 1999, ISBN 3-7776-0736-3 .
2. The values ​​for the properties (info box) are taken from www.webelements.com (Lanthanum) , unless otherwise stated .
3. 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.
4. Entry on lanthanum at WebElements, https://www.webelements.com , accessed on June 11, 2020.
5. ^ NN Greenwood, A. Earnshaw: Chemistry of the elements. 1st edition. VCH, Weinheim 1988, ISBN 3-527-26169-9 , p. 1219.
6. 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.
7. a b 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 .
8. a b Entry on lanthanum in the GESTIS substance database of the IFA , accessed on April 30, 2017(JavaScript required) .
9. ^ The Discovery and Naming of the Rare Earths - Elementymology & Elements Multidict. Retrieved March 24, 2019 .
10. NN GREENWOOD, A. EARNSHAW: Boron . In: Chemistry of the Elements . Elsevier, 1984, ISBN 978-0-08-030712-1 , pp. 155-242 .
11. ^ Mary Elvira Weeks: The discovery of the elements. XI. Some elements isolated with the aid of potassium and sodium: Zirconium, titanium, cerium, and thorium . In: Journal of Chemical Education . tape 9 , no. 7 July 1932, p. 1231 , doi : 10.1021 / ed009p1231 .
12. Lucien F. Trueb: The chemical elements, a foray through the periodic table. S. Hirzel Verlag, Stuttgart / Leipzig 1996, ISBN 3-7776-0674-X .
13. AP Drozdov, PP Kong, VS Minkov, SP Besedin, MA Kuzovnikov: Superconductivity at 250 K in lanthanum hydride under high pressures . In: Nature . tape 569 , no. 7757 , May 2019, p. 528-531 , doi : 10.1038 / s41586-019-1201-8 .