Cerium

Cerium

CAS:7440-45-1
Description: Soft, gray metal
Classification: Rare Earth (Lanthanide)
Date of Discovery: 1803
Discoverer: W. von Hisinger
Name Origin: asteroid Ceres, discovered in 1801

Atomic Number: 58
Number of Neutrons: 82
Atomic Mass: 140.115(4) amu
Melting Point: 798 °C
Boiling Point: 3424 °C
Density @ 25 °C: 6.770 g/cm³
Atomic volume: 20.67 cm³/mol
Electrical resistivity: 0.0115 10^-6/cm

Thermal conductivity: 0.114 W/cmK
Enthalpy of atomization: 381 kJ/mol (est)
Enthalpy of vaporization: 414.0 kJ/mol
Enthalpy of fusion: 5.460 kJ/mol
Specific heat capacity: 0.19 J/gK

Energy levels: 2-8-18-19-9-2
Electron configuration: [Xe]4f¹5d¹6s²
Crystal Structure: Cubic face centered
Atomic radius: 2.70 Å
Covalent radius: 1.65 Å
Oxidation States: +3, +4
Electronegativity, Pauling: 1.12
Electron affinity:
First ionization energy: 5.54 eV
2nd ionization energy: 10.851 eV
3rd ionization energy: 20.20 eV
Polarizability: 29.6 10^-24cm³

Isotope	Natural Abundance	Atomic Mass	Half-life	Decay Mode	Spin
¹²³Ce	122.936	3.8 s	⁺, EC
¹²⁴Ce	123.931	6 s	EC
¹²⁵Ce	124.929	10 s	⁺, EC	(5/2+)
¹²⁶Ce	125.9241	50 s	EC
¹²⁷Ce	126.9228	32 s	⁺, EC
¹²⁸Ce	127.9189	6 m	⁺, EC
¹²⁹Ce	128.9187	3.5 m	⁺, EC
¹³⁰Ce	129.9147	26 m	⁺, EC	0+
^131mCe	5 m	⁺, EC
¹³¹Ce	130.9144	10 m	⁺, EC
¹³²Ce	131.9115	3.5 h	EC	0+
^133mCe	1.6 h	⁺, EC	1/2+
¹³³Ce	132.9116	5.4 h	⁺; EC	9/2-
¹³⁴Ce	133.9090	3.16 d	EC	0+
^135mCe	20 s	IT	11/2-
¹³⁵Ce	134.90915	17.7 h	⁺; EC	1/2+
¹³⁶Ce	0.19(1)	135.90714	Stable	0+
^137mCe	1.43 d	IT; ⁺	11/2-
¹³⁷Ce	136.90778	9.0 h	⁺	3/2+
¹³⁸Ce	0.25(1)	137.90599	Stable	0+
^139mCe	56.4 s	IT; ^-	11/2-
¹³⁹Ce	138.90665	137.6 d	EC	3/2
¹⁴⁰Ce	88.48(10)	139.905435	Stable	0+
¹⁴¹Ce	140.908272	^-	7/2-
¹⁴²Ce	11.08(10)	141.909241	Stable	0+
¹⁴³Ce	142.912382	1.38 d	^-	3/2-
¹⁴⁴Ce	143.913643	284.6 d	^-	0+
¹⁴⁵Ce	144.91723	3.00 m	^-	3/2-
¹⁴⁶Ce	145.9187	13.5 m	^-	0+
¹⁴⁷Ce	146.9225	56 s	^-
¹⁴⁸Ce	147.9244	56 s	^-	0+
¹⁴⁹Ce	148.9283	5.2 s	^-
¹⁵⁰Ce	149.9302	4.4 s	^-
¹⁵¹Ce	150.9340	1.0 s	^-
¹⁵²Ce	151.9366	1.4 s	^-
Discovered in 1803 by Klaproth and by Berzelius and Hisinger; metal prepared by Hillebrand and Norton in 1875. Cerium is the most abundant of the metals of the so-called rare earths. It is found in a number of minerals including: allanite [ (Y,Ce,Ca)₂(Al,Fe³⁺)₃(SiO₄)₂3(OH)] (also known as orthite), monazite [Ce(PO₄)], bastnasite [(Ce,La)(CO₃)F], cerite {Ce³⁺9Fe³⁺(SiO₄)₆[(SiO₃)(OH)](OH)₃}, and samarskite [(Y,Ce,U,Fe)₃(Nb,Ta,Ti)₅O₁₆]. Monazite and bastnasite are presently the two most important sources of cerium. Large deposits of monazite found on the beaches of Travancore, India, in river sands in Brazil, and deposits of allanite in the western United States, and bastnasite in Southern California will supply cerium, thorium, and the other rare-earth metals for many years to come. Metallic cerium is prepared by metallothermic reduction techniques, such as by reducing cerous fluoride with calcium, or by electrolysis of molten cerous chloride or other cerous halides. The metallotherrnic technique is used to produce high-purity cerium. Cerium is especially interesting because of its variable electronic structure. The energy of the inner 4f level is nearly the same as that of the outer or valence electrons, and only small amounts of energy are required to change the relative occupancy of these electronic levels. This gives rise to dual valency states. For example, a volume change of about 10% occurs when cerium is subjected to high pressures or low temperatures. It appears that the valence changes from about 3 to 4 when it is cooled or compressed. The low temperature behavior of cerium is complex. Four allotropic modifications are thought to exist: cerium at room temperature and at atmospheric pressure is known as gamma () cerium. Upon cooling to -16 deg C, gamma cerium changes to beta () cerium. The remaining cerium starts to change to alpha () cerium when cooled to -172 deg C, and the transformation is complete at -269 deg C. cerium has a density of 8.16; delta () cerium exists above 726 °C. At atmospheric pressure, liquid cerium is more dense than its solid form at the melting point. Cerium is an iron-gray lustrous metal. It is malleable, and oxidizes very readily at room temperature, especially in moist air. Except for europium, cerium is the most reactive of the "rare-earth" metals. It slowly decomposes in cold water, and rapidly in hot water. Alkali solutions and dilute and concentrated acids attack the metal rapidly. The pure metal is likely to ignite if scratched with a knife. Ceric salts are orange red or yellowish; cerous salts are usually white. Cerium is a component of misch metal, which is extensively used in the manufacture of pyrophoric alloys for cigarette lighters, etc. Natural cerium is stable and contains four isotopes. Thirty-five other radioactive isotopes and isomers are known. While cerium is not radioactive, the impure commercial grade may contain traces of thorium, which is radioactive. The oxide is an important constituent of incandescent gas mantles and it is emerging as a hydrocarbon catalyst in "self-cleaning" ovens. In this application it can be incorporated into oven walls to prevent the collection of cooking residues. As ceric sulfate it finds extensive use 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. The oxide is finding increased use as a glass polishing agent instead of rouge, for it is much faster than rouge in polishing glass surfaces. Cerium, with other rare earths is used in carbon-arc lighting, especially in the motion picture industry. It is also finding use as an important catalyst in petroleum refining and in metallurgical and nuclear applications. LINKS: Glass Shops: Cerium Oxide and Radiation Influence of cerium on the recrystallization of aluminium Optical Properties of Cerium Doped Lutetium Borates OSHA Chemical Sampling Information: Cerium Return Sources for the information on this website include: Lide, David R., ed. CRC Handbook of Chemistry and Physics, 78th Ed., 1997-1998.

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