Oxygen-free metallic cesium can also be produced by the thermal decomposition of cesium azide (CsN45). The primary commercial source of metallic cesium is the mining of pollucite, while cesium radioisotopes are produced from waste from nuclear reactors. Bunsen and Kirchhoff gave the new element a name based on the Latin word Caesius (sky or celestial blue) for the two bright blue lines in its spectrum.Ĭesium is the most abundant element on earth and is found in the minerals pollucite, avogadrite, pezzottaite, londonite, rhodicite, beryl and some potassium ores. Cesium was also the first spectroscopically discovered element of the German scientists Robert Bunsen and Gustav Kirchhoff, who had invented the technology last year. Only one of the known isotopes of cesium is stable (133Cs), but with its 39 isotopes it is associated with xenon, the two elements with the largest amount of known isotopes. Mercury is the only element with a lower melting point. Cesium melts at 28 ° C, making it one of three elements (the others are gallium and mercury) that are liquid at or near room temperature. The heaviest of the stable alkali metals, cesium, has a silvery-golden appearance, is ductile and, with 0,2 on the Mohs scale, the softest element in the periodic table. Although cesium is only mildly toxic, it is considered hazardous because of its high reactivity and is usually packaged in glass ampoules in vacuo or under an inert gas such as argon. Although the element is only mildly toxic, it is a hazardous material as a metal and its radioisotopes present a high health risk in case of radiation leaks.With an electron in the sixth and outermost shell, cesium is the most electropositive of all stable elements in the periodic table: the metal is extremely pyrophoric, ignites spontaneously when in contact with air, and explodes violently in water or ice at any temperature above -116 ° C. The radioactive isotope caesium-137 has a half-life of about 30 years and is used in medical applications, industrial gauges, and hydrology. It has a range of applications in the production of electricity, in electronics, and in chemistry. Since the 1990s, the largest application of the element has been as caesium formate for drilling fluids. Since then, caesium has been widely used in atomic clocks. In 1967, a specific frequency from the emission spectrum of caesium-133 was chosen to be used in the definition of the second by the International System of Units. The first small-scale applications for caesium have been as a "getter" in vacuum tubes and in photoelectric cells. Two German chemists, Robert Bunsen and Gustav Kirchhoff, discovered caesium in 1860 by the newly developed method of flame spectroscopy. Caesium is mined mostly from pollucite, while the radioisotopes, especially caesium-137, a fission product, are extracted from waste produced by nuclear reactors. It is the least electronegative element that has stable isotopes, of which it has only one, caesium-133. The metal is extremely reactive and pyrophoric, reacting with water even at −116 ☌ (−177 ☏). Caesium is an alkali metal and has physical and chemical properties similar to those of rubidium and potassium. It is a soft, silvery-gold alkali metal with a melting point of 28 ☌ (82 ☏), which makes it one of only five elemental metals that are liquid at (or near) room temperature. Caesium or cesium ( /ˈsiːziəm/ see-zee-əm) is the chemical element with the symbol Cs and atomic number 55.
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