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Cerium


General
Name, Symbol, NumberCerium, 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 amu
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 ×10-3 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 293.15 K
Miscellaneous
Electronegativity 1.12 (Pauling scale)
Specific heat capacity 190 J/(kg*K)
Electrical conductivity 1.15 106/m ohm
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
isoNAhalf-life DMDE MeVDP
134Ce{syn.}3.16 days e capture0.500134La
136Ce0.19%Cerium is stable with 78 neutrons
138Ce0.25%Cerium is stable with 80 neutrons
139Ce{syn.}137.640 dayse capture0.278139La
140Ce88.48%Cerium is stable with 82 neutrons
141Ce{syn.}32.501 daysβ-0.581141Pr
142Ce11.08%> 5 E16 yearsβ-unknown142Nd
144Ce{syn.}284.893 daysβ-0.319144Pr
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.

Table of contents

Notable Characteristics Cerium is a silvery metallic element, belonging to the lanthanide group. It is used in some rare-earth alloys. The oxidized form is used in the glass industry. 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 decomposes 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 and some steels and irons.
    • Adding cerium to cast irons opposes graphitisation and produces a malleable iron.
    • In steels cerium can help reduce sulfides and oxides and degasifies.
    • 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 used in carbon-arc lighting[?], especially in the motion picture industry.
  • Cerium is a component of Mischmetal, which is extensively used in the manufacture of pyrophoric alloys for cigarette lighters.
  • The oxide is used in incandescent gas mantles.
  • The oxide is emerging as a hydrocarbon catalyst in self cleaning ovens, incorporated into oven walls.
  • Ceric 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.
  • The oxide is finding increased use as a glass polishing agent.
  • In glass, cerium oxide allows for selective absorption of ultraviolet light.
  • Cerium oxide is finding use as a petroleum cracking catalyst in petroleum refining.
  • Cerium(III) and Cerium(IV) compounds have uses as catalysts in organic synthesis.

History Cerium was discovered in Sweden by Jöns Jacob 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).

Biological Role Cerium serves no known biological function.

Occurrence Cerium is the most abundant of the rare earth elements, making up about 0.0046% of the Earth's crust. 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

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 amu (123-Ce) to 152 amu (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. External Links



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