CESIUM

The cesium is the chemical element with atomic number 55 and atomic weight of 132,905 uma. His symbol is Cs, and is most weighed of the alkaline metals in the group IA of the periodic table, with the exception of the francium (until February, 2007); The cesium was discovered by the chemist Robert Wilhem Bunsen and by Gustav Kirchhoff in the year 1860 by means of the use of the spectroscope. It comes from the Greek of caesium, sky blue, color that they give his you go out to the flame.
In the year 1967 it is found in the conference of weight and measures in Paris that a second is equal to 9.192.631.770 periods of radiation corresponding to the transition between both hyperthin levels of the fundamental condition of the isotope 133 of the atom of cesium (133Cs), measured to 0 K. Information obtained of http: // www.wikipedia.org/