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Caesium [Cs] locate me
CAS-ID: 7440-46-2
An: 55 N: 78
Am: 132.90545 g/mol
Group No: 1
Group Name: Alkali metal
Block: s-block  Period: 6
State: solid at 298 K (but melts only slightly above this temperature)
Colour: silvery gold Classification: Metallic
Boiling Point: 944K (671°C)
Melting Point: 301.59K (28.44°C)
Critical temperature: 1938K (1665°C)
Density: 1.93g/cm3
Discovery Information
Who: Gustov Kirchoff, Robert Bunsen
When: 1860
Where: Germany
Name Origin
Latin: caesius (sky blue); its salts turn flames blue.
 "Caesium" in different languages.
Sources
Found in pollucite and as trace in lepidolite (KLi2Al(Al,Si)3O10(F,OH)2). World production is around 20 tons per year.
Abundance
 Universe: 0.0008 ppm (by weight)
 Sun: 0.008 ppm (by weight)
 Carbonaceous meteorite: 0.14 ppm
 Earth's Crust: 3 ppm
 Seawater: 3 x 104 ppm
 Human:
   20 ppb by weight
   1 ppb by atoms
Uses
Used as a 'getter' to remove air traces in vacuum tubes. Since it ionizes readily, it is used as an ion rocket motor propellant. Also used in photoelectric cells, atomic clocks, infrared lamps.
Radioactive isotopes of caesium are used in the medical field to treat certain types of cancer.
This metal is also used in photoelectric cells due to its ready emission of electrons.
History
Caesium (Latin caesius meaning "sky blue" or "light blue") was spectroscopically discovered by Robert Bunsen and Gustav Kirchhoff in 1860 in mineral water from Durkheim, Germany. Its identification was based upon the bright blue lines in its spectrum and it was the first element discovered by spectrum analysis. The first caesium metal was produced in 1882 by Carl Setterberg. Historically, the most important use for caesium has been in research and development, primarily in chemical and electrical applications.
Notes
Also know as cesium in the United States.
Along with gallium, francium and mercury, caesium is among the only metals that are liquid at or near room temperature.
Caesium has at least 39 known isotopes which is more than any other element, except francium. Although only one of these is naturally occurring and stable, Cs-133.
Caesium is most notably used in atomic clocks, which are accurate to seconds in many thousands of years. SI defines the second as (exactly) 9,192,631,770 cycles of the radiation which corresponds to the transition between two energy levels of the ground state of the 133Cs atom.
Hazards
Caesium is considered highly toxic. Caesium reacts explosively in cold water and also reacts with ice at temperatures above -116°C.
Caesium is highly flammable in powder form.