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Cerium

From Academic Kids

LanthanumCeriumPraseodymium
Ce
Th  
 
 
image:Ce-TableImage.png
General
Name, Symbol, Number Cerium, Ce, 58
Chemical series Lanthanides
Group, Period, Block _ , 6, d
Density, Hardness 6689 kg/m3, 2.5
Appearance silvery white
Atomic properties
Atomic weight 140.116 u
Atomic radius (calc.) 185 (no data) pm
Covalent radius no data pm
van der Waals radius no data pm
Electron configuration [Xe]4f15d16s1
e- 's per energy level 2, 8,18,19, 9, 2
Oxidation states (Oxide) 3,4 (mildly basic)
Crystal structure Cubic face centered
Physical properties
State of matter solid (__)
Melting point 1071 K (1468 ?F)
Boiling point 3699 K (6199 ?F)
Molar volume 20.69 ×10-6 m3/mol
Heat of vaporization 414 kJ/mol
Heat of fusion 5.46 kJ/mol
Vapor pressure n/a Pa at 1071 K
Velocity of sound 2100 m/s at 20 ?C
Miscellaneous
Electronegativity 1.12 (Pauling scale)
Specific heat capacity 190 J/(kg·K)
Electrical conductivity 1.15 MS/m
Thermal conductivity 11.4 W/(m?K)
1st ionization potential 534.4 kJ/mol
2nd ionization potential 1050 kJ/mol
3rd ionization potential 1949 kJ/mol
4th ionization potential 3547 kJ/mol
Most stable isotopes
iso NA half-life DM DE MeV DP
134Ce {syn.} 3.16 days ε 0.500 134La
136Ce 0.19% Cerium is stable with 78 neutrons
138Ce 0.25% Cerium is stable with 80 neutrons
139Ce {syn.} 137.640 days ε 0.278 139La
140Ce 88.48% Cerium is stable with 82 neutrons
141Ce {syn.} 32.501 days β- 0.581 141Pr
142Ce 11.08% > 5 E16 years β- unknown 142Nd
144Ce {syn.} 284.893 days β- 0.319 144Pr
SI units & STP are used except where noted.

Cerium is a chemical element in the periodic table that has the symbol Ce and atomic number 58.

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Contents

Notable characteristics

Cerium is a silvery metallic element, belonging to the lanthanide group. It is used in some rare-earth alloys. It resembles iron in color and luster, but is soft, and both malleable and ductile. It tarnishes readily in the air.

Only europium is more reactive than cerium among rare earth elements. Alkali solutions and dilute and concentrated acids attack the metal rapidly. The pure metal is likely to ignite if scratched with a knife. Cerium oxidizes slowly in cold water and rapidly in hot water.

Because of the relative closeness of the 4f and outer shell orbitals in cerium, it exhibits an interestingly variable chemistry. For example, compression or cooling of the metal can change its oxidation state from about 3 to 4.

Cerium in the +3 oxidation state is referred to as cerous, while the metal in the +4 oxidation state is called ceric.

Cerium(IV) salts are orange red or yellowish, whereas cerium(III) salts are usually white.

Applications

Uses of cerium:

  • In metallurgy:
    • Cerium is used in making aluminium alloys.
    • Adding cerium to cast irons opposes graphitization and produces a malleable iron.
    • In steels, cerium degasifies and can help reduce sulfides and oxides.
    • Cerium is used in stainless steel as a precipitation hardening agent.
    • 3 to 4% cerium added to magnesium alloys, along with 0.2 to 0.6% zirconium, helps refine the grain and give sound casting of complex shapes. It also adds heat resistance to magnesium castings.
    • Cerium is used in alloys that are used to make permanent magnets.
    • Cerium is a major component of ferrocerium, also known as "lighter flint". Although modern alloys of this type generally use Mischmetal rather than purified cerium, it still is the most prevalent constituent.
    • Cerium is used in carbon-arc lighting, especially in the motion picture industry.
  • Cerium(IV) oxide
    • The oxide is used in incandescent gas mantles, such as the Welsbach mantle, where it was combined with Thorium, Lanthanum, Magnesium or Yttrium oxides .
    • The oxide is emerging as a hydrocarbon catalyst in self cleaning ovens, incorporated into oven walls.
    • Cerium(IV) oxide has largely replaced Rouge in the glass industry as a polishing abrasive.
    • Cerium(IV) oxide is finding use as a petroleum cracking catalyst in petroleum refining.
    • In glass, cerium(IV) oxide allows for selective absorption of ultraviolet light.
  • Cerium(IV) sulfate is used extensively as a volumetric oxidizing agent in quantitative analysis.
  • Cerium compounds are used in the manufacture of glass, both as a component and as a decolorizer.
  • Cerium compounds are used for the coloring of enamel.
  • Cerium(III) and cerium(IV) compounds such as cerium(III) chloride have uses as catalysts in organic synthesis.

History

Cerium was discovered in Sweden by J?Jakob Berzelius and Wilhelm von Hisinger, and independently in Germany by Martin Heinrich Klaproth, both in 1803. Cerium was so named by Berzelius after the asteroid Ceres, discovered two years earlier (1801).

Occurrence

Cerium is the most abundant of the rare earth elements, making up about 0.0046% of the Earth's crust by weight. It is found in a number of minerals including allanite (also known as orthite)—(Ca, Ce, La, Y)2(Al, Fe)3(SiO4)3(OH), monazite (Ce, La, Th, Nd, Y)PO4, bastnasite(Ce, La, Y)CO3F, hydroxylbastnasite (Ce, La, Nd)CO3(OH, F), rhabdophane (Ce, La, Nd)PO4-H2O, and synchysite Ca(Ce, La, Nd, Y)(CO3)2F. Monazite and bastnasite are presently the two most important sources of cerium.

Cerium is most often prepared via an ion exchange process that uses monazite sands as its cerium source.

Large deposits of monazite, allanite, and bastnasite will supply cerium, thorium, and other rare-earth metals for many years to come.

Compounds

Cerium has two common oxidation states, +3 and +4. The most common compound of cerium is cerium(IV) oxide (CeO2), which is used as "jeweller's rouge" as well as in the walls of some self-cleaning ovens. Two common oxidising agents used in titrations are ammonium cerium(IV) sulfate (ceric ammonium sulfate, (NH4)2Ce(SO4)3) and ammonium cerium(IV) nitrate (ceric ammonium nitrate or CAN, (NH4)2Ce(NO3)6). Cerium also forms a chloride, CeCl3 or cerium(III) chloride, used to facilitate reactions at carbonyl groups in organic chemistry. Other compounds include cerium(III) carbonate (Ce2(CO3)3), cerium(III) fluoride (CeF3), cerium(III) oxide (Ce2O3), as well as cerium(IV) sulfate (ceric sulfate, Ce(SO4)2) and cerium(III) triflate (Ce(OSO2CF3)3).

Isotopes

Naturally occurring cerium is composed of 3 stable isotopes and 1 radioactive isotope; 136-Ce, 138-Ce, 140-Ce, and 142-Ce with 140-Ce being the most abundant (88.48% natural abundance). 27 radioisotopes have been characterized with the most {abundant and/or stable} being 142-Ce with a half-life of >5E16 years, 144-Ce with a half-life of 284.893 days, 139-Ce with a half-life of 137.640, and 141-Ce with a half-life of 32.501 days. All of the remaining radioactive isotopes have half-lifes that are less than 4 days and the majority of these have half lifes that are less than 10 minutes. This element also has 2 meta states.

The isotopes of cerium range in atomic weight from 123 u (123-Ce) to 152 u (152-Ce).

Precautions

Cerium, like all rare earth metals, is of low to moderate toxicity. Cerium is a strong reducing agent and ignites spontaneously in air at 65-80 degrees C. Cerium may react explosively with zinc, and its reactions with bismuth and antimony are very exothermic. Fumes from cerium fires are toxic. Water should not be used to stop cerium fires, as cerium reacts with water to produce hydrogen gas. Workers exposed to cerium have experienced itching, sensitivity to heat, and skin lesions. Animals injected with large doses of cerium have died due to cardiovascular collapse.

Cerium(IV) oxide is a powerful oxidizing agent at high temperatures and will react with combustible organic materials. While cerium is not radioactive, the impure commercial grade may contain traces of thorium, which is radioactive. Cerium serves no known biological function.

References

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