Cerium
Symbol: Ce
Atomic Number: 58
Atomic Mass: 140.116 amu (atomic mass units)
Melting Point: 795.0 C (1068.15 K, 1463.0 F)
Boiling Point: 3257.0 C (3530.15 K, 5894.6 F)
Number of Protons: 58
Number of Electrons: 58
Number of Neutrons: 82
Classification: Rare Earth Metal
Crystal Structure: Cubic
Density @ 293 K: 6.773 grams per cubic centimeter
Color: Gray
Cerium is the most common of the rare earth elements and is a member of the lanthanide or lanthanoid series. It was discovered in 1803 by the Swedish chemists Jons Jacob Berzelius and Wilhelm von Hisinger and in an independent study by the German chemist Heinrich Klaproth. A sample of the metal was first prepared in 1875 by Hillebrand and Norton. It was named after the asteroid Ceres which had been discovered in 1801.
The element is a malleable, steel gray metal. It oxidizes in air especially in the presence of moisture. Cerium is one of the most reactive of the rare earth elements, only europium is more reactive. It will decompose slowly in cold water and rapidly in hot water. The metal is attacked by alkaline solutions as well as by both concentrate and dilute acids. When scratched with a knife cerium can ignite.
Cerium has a variable electron structure. The energy of the electrons in the inner or 4f level is similar to that of the outer or valence electron level. Small amounts of energy can induce a change in the occupancy of the electronic levels. This leads to cerium having a dual valency state. One of the effects of this is that at low temperatures or high pressure there is a 10% change in the volume of cerium.
Ceric salts tend to be orange, red or yellow in color while cerous salts are usually white.
Naturally occurring cerium is made up of four isotopes. Cerium-140 accounts for 88.45% and cerium-138 for 0.251%, both of these isotopes are stable. The remaining cerium is made of the unstable isotopes cerium-136 (0.185%) and cerium-142 (11.114%) both of which have extremely long half-lives. Many other unstable isotopes of cerium have been produced with atomic masses ranging from 119 to 157.
Cerium can be extracted from a number of mineral ores but its main sources are the ores monazite, allanite and bastnasite. Some of these ores also contain the radioactive element thorium and low grade industrial quality cerium sometimes contains thorium. Pure cerium can be extracted using metallothermic reduction methods.
A number of uses for cerium have been identified.
* It along with other rare earth elements forms the alloy misch metal which is used to make flints for cigarette lighters.
* Cerium is one of the rare earth elements used to provide arc lights for the motion picture industry.
* Petroleum refining uses cerium as a catalyst.
* Cerium oxide is used as part of the surface of self cleaning ovens. It is also used to make incandescent lantern mantles and to polish glass.
* Cerium compounds are used to both manufacture and decolorize glass.
* In quantitative chemical analysis ceric sulfate is used as a volumetric oxidizing agent.
