CHEM-I-PAGE

Cerium                                                                     

Standard Sate: solid at 298k

Color: silvery white

Metallic cerium is prepared by reduction techniques, such as by reducing cerous fluoride with calcium, or by electrolysis of molten cerous chloride or other cerous halides. Cerium is an iron-grey lustrous metal. It is malleable, and oxidises 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 may ignite when scratched with a knife. It is the most abundant of the rare earth metals and is found in minerals including allanite, monazite, cerite, and bastanite. There are large deposits found in India, Brazil and the USA.

(Ce), chemical element, most abundant of the rare-earth metals of
transition Group IIIb of the periodic table. Cerium is iron gray in
colour and about as soft and ductile as tin. It oxidizes slowly in air,
rapidly reacts with water to yield hydrogen, and burns brilliantly when
heated. Cerium as the oxide (ceria) was discovered (1803) by J�ns
Jacob Berzelius and Wilhelm Hisinger working together, and
independently by Martin Klaproth. It was named after the asteroid
Ceres, which was discovered in 1801. Ceria, the second rare earth to
be discovered (yttria was first), turned out to be a mixture of oxides
from which seven elements were separated during the course of the
next century. These other elements were the lighter rare-earth
metals, from lanthanum (atomic number 57) to gadolinium (atomic
number 64), with the exception of promethium. Cerium occurs in
monazite, bastnaesite, and many other minerals. It also is found
among the fission products of uranium, plutonium, and thorium.
Cerium is about as abundant as copper and nearly three times as
abundant as lead in the igneous rocks of Earth's crust. Four stable
isotopes occur in nature: cerium-140 (88.48 percent), cerium-142
(11.07 percent), cerium-138 (0.250 percent), and cerium-136 (0.193
percent). The metal itself is prepared by electrolysis of the anhydrous
fused halides or by thermoreduction of the halides with alkali or
alkaline-earth metals. It exists in four allotropic (structural) forms.

Cerium and its compounds have a number of practical applications.
The dioxide is employed in the optics industry for fine polishing of
glass (replacing rouge); it is also used as an opacifier in porcelain
coatings and as a decolorizer in glass manufacturing. Cerium nitrate
has been used in the manufacture of incandescent-gas mantles; other
salts are employed in the ceramic, photographic, and textile industries.
The metal serves as an ingredient in the carbon-impregnated arc
lamps that have been used for illumination in the motion-picture,
television, and related industries. Together with the other rare-earth
metals, cerium is a constituent of numerous ferrous and nonferrous
alloys; a superior high-temperature alloy for jet engines contains about
3 percent cerium with magnesium. Misch metal (50 percent cerium)
is used for cigarette-lighter flints, in tracer bullets, and in electron-tube
manufacture as a getter, which removes traces of oxygen.

Along with praseodymium and terbium, cerium is different from the
other trivalent rare earths in that it forms compounds in which it is
tetravalent; it is the only rare earth that exhibits a +4 oxidation state in
solution. Tetravalent (ceric) salts, which are powerful but stable
oxidizing agents, are used in analytical chemistry to determine
oxidizable substances such as iron(II). Most cerium(IV) salts are
orange to yellow in colour, as are solutions containing the Ce4+ ion.
Cerium(III) behaves as a typical rare earth; its compounds are usually
white.


atomic number58

atomic weight140.120

melting point798 C

boiling point3,257 C

specific gravity6.771 (25 C)

valence3, 4

electronic config. 2-8-18-20-8-2 or

(Xe)4f 25d06s2

"cerium" Encyclop�dia Britannica Online.

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