58
  Ce  
140.116000
Cerium

Name: Cerium
Symbol: Ce
Atomic Number: 58
Atomic Weight: 140.116000
Family:  Rare Earth Elements
CAS RN: 7440-45-1
Description: A malleable silvery white rare-earth metal.
State (25C): Solid
Oxidation states: +3, +4

Molar Volume: 20.7 cm3/mole
Valence Electrons: 4f26s2

Boiling Point: 3699oK, 3426oC, 6199oF
Melting Point: 1071oK, 798oC, 1468oF

Electrons Energy Level: 2, 8, 18, 19, 9, 2
Isotopes 35 + 4 Stable + 5 meta states 
Heat of Vaporization: 414 kJ/mol
Heat of Fusion: 5.46 kJ/mol
Density 6.757 g/cm3 @ 300oK
Specific Heat 0.19 J/gK
Atomic Radius: 2.7
Ionic Radius: 1.034
Electronegativity: 1.12 (Pauling), 1.06 (Allrod Rochow)
57
La
138.9
58
Ce
140.1
59
Pr
140.9
60
Nd
144.2
61
Pm
(145)
62
Sm
150.4
63
Eu
152.0
64
Gd
157.3
65
Tb
158.9
66
Dy
162.5
67
Ho
164.9
68
Er
167.3
69
Tm
168.9
70
Yb
173.0
71
Lu
175.0

1s2 2s2p6 3s2p6d10 4s2p6d10f1 5s2p6d1 6s2

History

Cerium was discovered, in 1803, in Sweden by Jns Jakob Berzelius and Wilhelm von Hisinger, and independently in Germany by Martin Heinrich Klaproth, but not isolated as a metal until 1875 by Hillebrand and Norton.  Cerium was so named by Berzelius after the dwarf planet Ceres, discovered two years earlier in 1801.

180px-Martin_Heinrich_Klaproth.jpg (7368 bytes)

Martin Heinrich Klaproth

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.

1s2
2s2 2p6
3s2 3p6 3d10
4s2 4p6 4d10 4f1
5s2 5p6 5d1
6s2

Although cerium belongs to chemical elements group called rare earth metals, it is not rare at all.  Cerium is available in relatively large quantities (68 ppm in Earth’s crust); in fact it is more common than lead.

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.

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, zircon (ZrSiO4), and synchysite Ca(Ce, La, Nd, Y)(CO3)2F. Monazite and bastnasite are presently the two most important sources of cerium.

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 -16oC, gamma cerium changes to beta cerium.  The remaining gamma cerium starts to change to alpha cerium when cooled to -172oC, and the transformation is complete at -269oC.  Alpha Cerium has a density of 8.16; delta cerium exists above 726oC.  At atmospheric pressure, liquid cerium is more dense than its solid form at the melting point. 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. 

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. 

Applications

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 oxidizing 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; 136Ce, 138Ce, 140Ce, and 142Ce with 140Ce being the most abundant (88.48% natural abundance).  30 radioisotopes have been characterized with the most {abundant and/or stable} being 142Ce with a half-life of greater than 51016 years, 144Ce with a half-life of 284.893 days, 139Ce with a half-life of 137.640 days, and 141Ce with a half-life of 32.501 days.  All of the remaining radioactive isotopes have half-lives that are less than 4 days and the majority of these have half-lives that are less than 10 minutes.  This element also has 2 meta states.

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

atom.gif (700 bytes)

Isotope  
Atomic Mass
 
Half-Life
119Ce 118.95276 ~200 ms
120Ce 119.94664 ~250 ms
121Ce 120.94342 1.1 seconds
122Ce 121.93791 ~2 seconds
123Ce 122.93540 3.8 seconds
124Ce 123.93041 9.1 seconds
125Ce 124.92844 9.3 seconds
126Ce 125.92397 51.0 seconds
127Ce 126.92273 29 seconds
128Ce 127.91891 3.93 minutes
129Ce 128.91810 3.5 minutes
130Ce 129.91474 22.9 minutes
131Ce 130.91442 10.2 minutes
131mCe   5.0 minutes
132Ce 131.911460 3.51 hours
133Ce 132.911515 97 minutes
133mCe   4.9 hours
134Ce 133.908925 3.16 days
135Ce 134.909151 17.7 hours
135mCe   20 seconds
136Ce 135.907172 Stable
137Ce 136.907806 9.0 hours
137mCe   34.4 hours
138Ce 137.905991 Stable
139Ce 138.906653 137.641 days
139mCe   56.54 seconds
140Ce 139.9054387 Stable
141Ce 140.9082763 32.508 days
142Ce 141.909244 Stable
143Ce 142.912386 33.039 hours
144Ce 143.913647 284.91 days
145Ce 144.91723 3.01 minutes
146Ce 145.91876 13.52 minutes
147Ce 146.92267 56.4 seconds
148Ce 147.92443 56 seconds
149Ce 148.9284 5.3 seconds
150Ce 149.93041 4.0 seconds
151Ce 150.93398 1.02 seconds
152Ce 151.93654 1.4 seconds
153Ce 152.94058 ~500 ms
154Ce 153.94342 ~300 ms
155Ce 154.94804 ~200 ms
156Ce 155.95126 ~150 ms
157Ce 156.95634 ~50 ms

Precautions

40px-Skull_and_crossbones.svg.jpg (1420 bytes) 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 to 80C.   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.

80px-Flammable.jpg (2186 bytes) It is much more reactive than iron, however, readily oxidizing in moist air and releasing hydrogen from boiling water. Friction from abrading a sample can cause it to ignite.

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.

*Mischmetal (from German : Mischmetall - "mixed metals") is an alloy of rare earth elements in various naturally-occurring proportions. It is also called cerium mischmetal, rare earth mischmetal or misch metal. A typical composition includes approximately 50% cerium and 45% lanthanum, with small amounts o neodymium and praseodymium.  Its most common use is in the "flint" ignition device of many lighters and torches, although an alloy of only rare-earth elements would be too soft to give good sparks. For this purpose, it is blended with iron oxide and magnesium oxide to form a harder material known as ferrocerium.

Mischmetal is used in the preparation of virtually all rare earth elements. This is because such elements are nearly identical in most chemical processes, meaning that ordinary extraction processes do not distinguish them. Highly specialized processes, such as those developed by Carl Auer von Welsbach, exploit subtle differences in solubility to separate mischmetal into its constituent elements, with each step producing only an incremental change in composition. Such processes later informed Marie Curie in her search for new elements.

Mischmetal is widely applied in steel foundaries for making FeSiMg alloy and it is used to remove free oxygen and sulfur by forming stable oxysulfides and by tying up undesirable trace elements, such as lead and antimony.

Mischmetal can be further processed to various shapes of ingots, wires, slabs, rods, and discs.

atom.gif (700 bytes)

Cerium Data

 

Atomic Structure

Atomic Radius (): 2.7
Atomic Volume cm3/mol: 20.67cm3/mol
Covalent Radius: 1.65
Crystal Structure: Face-Centered Cubic (FCC)
Ionic Radius: 1.034

Chemical Properties

Electrochemical Equivalents: 1.7426 g/amp-hr
Electron Work Function: 2.84eV
Electronegativity: 1.12 (Pauling), 1.06 (Allrod Rochow)
Heat of Fusion: 5.46 kJ/mol
First Ionization Potential: 5.54
Second Ionization Potential: 10.851
Third Ionization Potential: 20.2
Valence Electron Potential (-eV): 41.78
Ionization Energy (eV): 5.539 eV

Physical Properties

Atomic Mass Average: 140.115
Boiling Point: 3699oK, 3426oC, 6199oF
Melting Point: 1071oK, 798oC, 1468oF
Heat of Vaporization: 414 kJ/mol
Coefficient of Lineal Thermal Expansion/K-1: 8.5E-6
Electrical Conductivity: 0.0115 106/cm
Thermal Conductivity: 0.114 W/cmK
Density: 6.757 g/cm3 @ 300oK
Enthalpy of Atomization: 381 kJ/mole @ 25C
Enthalpy of Fusion: 5.46 kJ/mole
Enthalpy of Vaporization: 414 kJ/mole
Molar Volume: 20.7 cm3/mole
Specific Heat: 0.19 J/gK
Vapor Pressure: unknown
Estimated Crustal Abundance: 6.65101 milligrams per kilogram
Estimated Oceanic Abundance: 1.210-6 milligrams per liter

Miscellaneous

Fusion Heat: 5.2 kJ/mol
Evaporation Heat: 398 kJ/mol
First Ionizing Energy (kJ/mol): 540.1
Electronic Configuration: [Xe] 4f1 5d1 6s2
Lattice Constant: 5.160
1st. Ionization Energy: 540.1 kJ/mol