# cerium

properties
[ Xe ] 4 f 1 5 d 1 6 s 2
58 Ce
General
Name , symbol , atomic number Cer, Ce, 58
Element category Lanthanoids
Group , period , block La , 6 , f
Appearance silvery white
CAS number 7440-45-1
EC number 231-154-9
ECHA InfoCard 100.028.322
Mass fraction of the earth's envelope 43 ppm
Atomic
Atomic mass 140.116 (1) and
Electron configuration [ Xe ] 4 f 1 5 d 1 6 s 2
1. Ionization energy 5.5386 (4) eV534.39 kJ / mol
2. Ionization energy 10.956 (20) eV1 057.09 kJ / mol
3. Ionization energy 20th.1974 (25) eV1 948.75 kJ / mol
4. Ionization energy 36.906 (9) eV3 560.9 kJ / mol
5. Ionization energy 65.55 (25) eV6 320 kJ / mol
Physically
Physical state firmly
Crystal structure Cubic area-centered
density 6.773 g / cm 3 (25 ° C )
Mohs hardness 2.5
magnetism paramagnetic ( Χ m = 1.4 10 −3 )
Melting point 1068 K (795 ° C)
boiling point 3743 K (3470 ° C)
Molar volume 20.69 · 10 −6 m 3 · mol −1
Heat of evaporation 398 kJ / mol
Heat of fusion 5.5 kJ mol −1
Speed ​​of sound 2100 m s −1 at 293.15 K.
Electric conductivity 1.35 · 10 6 A · V −1 · m −1
Thermal conductivity 11 W m −1 K −1
Chemically
Oxidation states 3 , 4
Normal potential −2.34 V (Ce 3+ + 3 e - → Ce)
Electronegativity 1.12 ( Pauling scale )
Isotopes
isotope NH t 1/2 ZA ZE (M eV ) ZP
134 Ce {syn.} 3.16 d ε 0.500 134 La
135 Ce {syn.} 17.7 h ε 2.026 135 La
136 Ce 0.19% Stable
137 Ce {syn.} 9.0 h ε 1.222 137 La
138 Ce 0.25% Stable
139 Ce {syn.} 137.64 d ε 0.581 139 La
140 Ce 88.48% Stable
141 Ce {syn.} 32.501 d β - 0.581 141 Pr
142 Ce 11.08% 5 · 10 16 a β - β - 4.505 142 Nd
143 Ce {syn.} 33.039 h β - 1.462 143 Pr
144 Ce {syn.} 284,893 d β - 0.319 144 pr
For other isotopes see list of isotopes
safety instructions
GHS labeling of hazardous substances

danger

H and P phrases H: 228
P: 231 + 232-233-280-370 + 378-402 + 404-501
As far as possible and customary, SI units are used.
Unless otherwise noted, the data given apply to standard conditions .

Cer [ t͡seːɐ̯ (also] cerium or cerium called) is a chemical element with the element symbol Ce and atomic number 58. In the periodic table , it is in the group of the lanthanides and is also one of the rare earth metals .

## history

Cer metallic bright

Cer was discovered in 1803 by Jöns Jakob Berzelius and Wilhelm von Hisinger and at the same time by Martin Heinrich Klaproth . It was named after the dwarf planet Ceres . Carl Gustav Mosander succeeded in producing the element in 1825 by reducing the chloride with sodium .

## Occurrence

In nature, cerium occurs together with other lanthanoids in so-called cerite earths , such as in allanite (Ca, Ce, La, Y) 2 (Al, Fe) 3 (SiO 4 ) 3 (OH), in monazite (Ce, La , Th, Nd, Y) PO 4 as well as in the bastnäsite (Ce, La, Y) CO 3 F. Cer is the most common element of the lanthanides and is ranked 28th in the element frequency in the earth's crust, down to a depth of 16 km calculated, it is represented at 68 g / t and is therefore more common than tin or lead. Important deposits are located in Scandinavia, the USA, the Congo, South Africa and India. The world-wide known cerium reserves are estimated at 40 million tons. Cerium is one of the so-called light rare earths that the BGR assessed in 2014 as uncritical with regard to the supply situation. Elemental (“solid”) cerium does not occur on earth because of its high reactivity. However, it has been found in microscopic particles in lunar rocks. It is probably caused by impact events on the moon.

## Extraction and manufacture

After a complex separation of the cerium companion, the oxide is converted with hydrogen fluoride to cerium fluoride . It is then reduced to cerium with calcium to form calcium fluoride . The removal of remaining calcium residues and impurities takes place in an additional remelting process in a vacuum. The annual world production is around 24,000 t.

## properties

Phase diagram of cerium

### Physical Properties

Four modifications of cerium are known:

${\ displaystyle \ mathrm {(\ alpha) Cer \ _ {\ overrightarrow {-196 \, ^ {\ circ} \ mathrm {C}}} \ (\ beta) Cer \ _ {\ overrightarrow {-24 \, ^ {\ circ} \ mathrm {C}}} \ (\ gamma) Cer \ _ {\ overrightarrow {726 \, ^ {\ circ} \ mathrm {C}}} \ (\ delta) Cer}}$

The silvery white shiny metal is the second most reactive element of the lanthanoids after europium . Above 150  ° C it burns with a violent glow to form ceria . It reacts with water to form cerium (III) hydroxide .

### Chemical properties

Cerium occurs in compounds as a trivalent colorless or tetravalent yellow to orange-colored cation .

When exposed to heat, it is very strongly attacked by ethanol and water. It is also strongly attacked in alkalis with the formation of cerium hydroxides. In acids it is dissolved into salts.

## use

Since the chemical properties of the rare earths are similar, metallic cerium is rarely used in its pure form, but in the mixture in which it is obtained during manufacture from the rare earth minerals, the so-called mischmetal .

Small amounts of (more or less pure) cerium compounds give other materials certain properties:

## Biological importance

In 2013, an enzyme that requires cerium ions for its function was first discovered in bacteria . The bacteria of the species Methylacidiphilum fumariolicum were isolated from volcanic mud pools in Italy. You need cerium to build up methanol dehydrogenase , an enzyme in methane metabolism . The ion has the role that calcium ions take over in similar enzymes in other bacteria.

## safety instructions

Like all lanthanoids, cerium is slightly toxic. Metallic cerium can ignite from 65 ° C. As a finely divided metal, it can heat up in the air without the use of energy and finally ignite. The readiness for ignition depends u. a. very much on the grain size and the degree of distribution. Cerfires must not be extinguished with water, as gaseous hydrogen develops.

### Other connections

Commons : Cer  - collection of pictures, videos and audio files
Wiktionary: Cer  - 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 ​​of the atomic and physical properties (info box) are (unless otherwise stated) taken from www.webelements.com (Cer) .
3. entry on cerium 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 cerium 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. 1579.
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 cerium, chips in the GESTIS substance database of the IFA , accessed on April 2, 2018(JavaScript required) .
9. Federal Institute for Geosciences and Raw Materials: Current BGR research: China's share of global rare earth production is falling only slowly. March 12, 2014.