| | | General | | Name, Symbol, Number | Caesium, Cs, 55 | | Series | Alkali metals | | Group, Period, Block | 1(IA), 6, s | | Density, Hardness | 1879 kg/m3, 0.2 | | Appearance | silvery gold
| | Atomic properties | | Atomic weight | 132.90545 amu | | Atomic radius (calc.) | 260 (298) pm | | Covalent radius | 225 pm | | van der Waals radius | no data | | Electron configuration | [Xe]6s1 | | e- s per energy level | 2, 8, 18, 18, 8, 1 | | Oxidation states (Oxide) | 1 (strong base) | | Crystal structure | Cubic body centered | | Physical properties | | State of matter | liquid | | Melting point | 301.59 K (83.19 °F) | | Boiling point | 944 K (1240 °F) | | Molar volume | 70.94 ×10-6 m3/mol | | Heat of vaporization | 67.74 kJ/mol | | Heat of fusion | 2.092 kJ/mol | | Vapor pressure | 2.5 kPa | | Speed of sound | no data | | Miscellaneous | | Electronegativity | 0.79 (Pauling scale) | | Specific heat capacity | 240 J/(kg*K) | | Electrical conductivity | 4.89 106/m ohm | | Thermal conductivity | 35.9 W/(m*K) | | 1st ionization potential | 375.7 kJ/mol | | 2nd ionization potential | 2234.3 kJ/mol | | 3rd ionization potential | 3400 kJ/mol | | Most stable isotopes | | | | SI units & STP are used except where noted. | Caesium (spelt cesium in the USA, is pronounced /'siːzɪəm/, though it goes against Latin phonetics) is a chemical element in the periodic table that has the symbol Cs and atomic number 55. It is a soft silvery-gold Alkali metal which is one of at least three metals that are liquid at room temperature. This element is most notably used in atomic clocks.
Caesium is sometimes spelt cesium, especially in North American English, but caesium is the official name preferred by IUPAC, although since 1993 it has recognized cesium as a variant.
Notable characteristics
The electromagnetic spectrum of caesium has two bright lines in the blue part of the spectrum along with several other lines in the red, yellow, and green. This metal is silvery gold in color and is both soft and ductile. Caesium is also the most electropositive and most alkaline chemical element and also has the least ionization potential of all the elements, except for francium. Caesium is the least abundant of the five non-radioactive alkali metals. (Technically, francium is the least common alkali metal, but since it is highly radioactive with less than an ounce in the entire earth at one time, its abundance can be considered zero in practical terms.)
Along with gallium and mercury, caesium is among the only metals that are liquid at or near room temperature. Caesium reacts explosively in cold water and also reacts with ice at temperatures above -116°C. Caesium hydroxide (CsOH) is the strongest base known to exist and attacks glass.
Applications Caesium is most notably used in atomic clocks, which are accurate to seconds in many thousands of years.
More recently this metal has been used in ion propulsion systems.
History Caesium (Latin caesius meaning "sky blue") was spectroscopically discovered by Robert Bunsen and Gustav Kirchhoff in 1860 in mineral water from Dürkheim, 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 1881. Since 1967, the International System of Units (SI) has defined the second as 9,192,631,770 cycles of the radiation which corresponds to the transition between two energy levels of the ground state of the Caesium-133 atom. Historically, the most important use for caesium has been in research and development, primarily in chemical and electrical applications.
Occurrence Pollucite, a caesium mineral An alkali metal, caesium occurs in lepidolite, pollucite (hydrated silicate of aluminium and caesium) and within other sources. One of the world's most significant and rich sources of this metal is located at Bernic Lake in Manitoba. The deposits there are estimated to contain 300,000 tons of pollucite at an average of 20% caesium.
It can be isolated by electrolysis of fused cyanide and in a number of other ways. Exceptionally pure and gas-free caesium can be made by the thermal decomposition of caesium azide. The primary compounds of caesium are its chloride and its nitrate. The price of caesium in 1997 was about $US 30 per gram.
Isotopes Caesium has 32 known isotopes which is more than any other element, except francium. The atomic masses of these isotopes range from 114 to 145. Even though this element has the largest number of isotopes, it has only one naturally occurring stable isotope, Cs-133. The radiogenic isotope Cs-137 has been used in hydrologic studies, analogous to the use of H-3 (tritium). Cs-137 is produced from detonation of nuclear weapons and emissions from nuclear power plants, and notably from the 1986 Chernobyl explosion. Beginning in 1954 with the commencement of nuclear testing, Cs-137 was released into the atmosphere where it is absorbed readily into solution. Once Cs-137 enters the ground water, it is deposited on soil surfaces and removed from the landscape primarily by particle transport. As a result, the input function of these isotopes can be estimated as a function of time.
Precautions Caesium is highly explosive in cold water. Caesium should be considered highly toxic. Some of its radioisotopes are even more toxic. Caesium hydroxide is an extremely strong base, and can attack glass.
See also - Goiânia accident - a major radioactive contamination incident involving a small rod of caesium chloride
References
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