Caesium or cesium (see-zee-əm) is the chemical element with the symbol "Cs" and atomic number 55. It is a soft, silvery-gold alkali metal with a melting point of 28 °C (82 °F), which makes it one of only five elemental metals that are liquid at (or near) room temperature.Caesium is an alkali metal and has physical and chemical properties similar to those of rubidium and potassium. The metal is extremely reactive and pyrophoric, reacting with water even at −116 °C (−177 °F). It is the least electronegative element that has stable isotopes, of which it has only one, caesium-133. Caesium is mined mostly from pollucite, while the radioisotopes, especially caesium-137, a fission product, are extracted from waste produced by nuclear reactors. Two German chemists, Robert Bunsen and Gustav Kirchhoff, discovered caesium in 1860 by the newly developed method of flame spectroscopy. The first small-scale applications for caesium have been as a "getter" in vacuum tubes and in photoelectric cells. 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. Since then, caesium has been widely used in atomic clocks. Since the 1990s, the largest application of the element has been as caesium formate for drilling fluids. It has a range of applications in the production of electricity, in electronics, and in chemistry. The radioactive isotope caesium-137 has a half- life of about 30 years and is used in medical applications, industrial gauges, and hydrology. 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. Caesium forms alloys with the other alkali metals as well as with gold, and amalgams with mercury. At temperatures below 650 °C (1,202 °F), it alloys with cobalt, iron, molybdenum, nickel, platinum, tantalum or tungsten. It forms well-defined intermetallic compounds with antimony, gallium, indium and thorium, which are photosensitive. The chemistry of caesium is similar to that of other alkali metals, but is more closely similar to that of rubidium, the element above caesium in the periodic table.Some small differences arise from the fact that it has a higher atomic mass and is more electropositive than other (non- radioactive) alkali metals.Caesium is the most electropositive stable chemical element.The caesium ion is also larger and less "hard" than those of the lighter alkali metals. In 1860, Robert Bunsen and Gustav Kirchhoff discovered caesium in the mineral water from Dürkheim, Germany. Due to the bright blue lines in its emission spectrum, they chose a name derived from the Latin word caesius, meaning sky-blue. Caesium was the first element to be discovered spectroscopically, only one year after the invention of the spectroscope by Bunsen and Kirchhoff. To obtain a pure sample of caesium, 44,000 litres (9,700 imp gal; 12,000 US gal) of mineral water had to be evaporated to yield 240 kilograms (530 lb) of concentrated salt solution. The alkaline earth metals were precipitated either as sulfates or oxalates, leaving the alkali metal in the solution. After conversion to the nitrates and extraction with ethanol, a sodium-free mixture was obtained. From this mixture, the lithium was precipitated by ammonium carbonate. Potassium, rubidium and caesium form insoluble salts with chloroplatinic acid, but these salts show a slight difference in solubility in hot water. Therefore, the less-soluble caesium and rubidium hexachloroplatinate ((Cs,Rb)2PtCl6) could be obtained by fractional crystallization. After reduction of the hexachloroplatinate with hydrogen, caesium and rubidium could be separated by the difference in solubility of their carbonates in alcohol. The process yielded 9.2 grams (0.32 oz) of rubidium chloride and 7.3 grams (0.26 oz) of caesium chloride from the initial 44,000 liters of mineral water. The two scientists used the caesium chloride thus obtained to estimate the atomic weight of the new element at 123.35 (compared to the currently accepted one of 132.9).They tried to generate elemental caesium by electrolysis of molten caesium chloride, but instead of a metal, they obtained a blue homogenous substance which "neither under the naked eye nor under the microscope" showed the slightest trace of metallic substance;" as a result, they assigned it as a subchloride (Cs2Cl). In reality, the product was probably a colloidal mixture of the metal and caesium chloride.The electrolysis of the aqueous solution of chloride with a mercury anode produced a caesium amalgam which readily decomposed under the aqueous conditions. The pure metal was eventually isolated by the German chemist Carl Setterberg while working on his doctorate with Kekulé and Bunsen. In 1882 he produced caesium metal by electrolyzing caesium cyanide, and thus avoiding the problems with the chloride. Historically, the most important use for caesium has been in research and development, primarily in chemical and electrical fields. Very few applications existed for caesium until the 1920s when it became used in radio vacuum tubes. It had two functions: as a getter it removed excess oxygen after manufacture, and as a coating on the heated cathode, it increased its electrical conductivity. Caesium did not become recognized as a high-performance industrial metal until the 1950s.[60] Applications of non-radioactive caesium included photoelectric cells, photomultiplier tubes, optical components of infrared spectrophotometers, catalysts for several organic reactions, crystals for scintillation counters, and in magnetohydrodynamic power generators. Since 1967, the International System of Measurements has based its unit of time, the second, on the properties of caesium. The International System of Units (SI) defines the second as 9,192,631,770 cycles of the radiation, which corresponds to the transition between two hyperfine energy levels of the ground state of the caesium-133 atom. Caesium-137 is a very common radioisotope used as a gamma-emitter in industrial applications. Its advantages include a half-life of roughly 30 years, its availability from the nuclear fuel cycle, and having 137Ba as stable end product. The high water solubility is a disadvantage which makes it incompatible with irradiation of food and medical supplies. Caesium compounds are rarely encountered by most people, but most caesium compounds are mildly toxic because of chemical similarity of caesium to potassium. Exposure to large amounts of caesium compounds can cause hyperirritability and spasms, but as such amounts would not ordinarily be encountered in natural sources, caesium is not a major chemical environmental pollutant. References: ^ Band, A.; Albu-Yaron, A.; Livneh, T.; Cohen, H.; Feldman, Y.; Shimon, L.; Popovitz-Biro, R.; Lyahovitskaya, V. et al. (2004). "Characterization of Oxides of Cesium". The Journal of Physical Chemistry B 108 (33): 12360–12367. doi:10.1021/jp036432o. ^ Brauer, G. (1947). "Untersuchungen ber das System Csium-Sauerstoff". Zeitschrift fr anorganische Chemie 255: 101. doi:10.1002/zaac.19472550110. ^ Busso, M.; Gallino, R.; Wasserburg, G. J. (1999). "Nucleosynthesis in Asymptotic Giant Branch Stars: Relevance for Galactic Enrichment and Solar System Formation" (PDF). Annula Review of Astronomy and Astrophysics 37: 239–309. Bibcode 1999ARA&A..37..239B. doi:10.1146/annurev.astro.37.1.239. Retrieved 2010-02-20. ^ Arnett, David (1996). Supernovae and Nucleosynthesis: An Investigation of the History of Matter, from the Big Bang to the Present. Princeton University Press. p. 527. ISBN 0-691-01147-8. ^ Goff, C; Matchette, Michael A.; Shabestary, Nahid; Khazaeli, Sadegh (1996). "Complexation of caesium and rubidium cations with crown ethers in N,N-dimethylformamide". Polyhedron 15 (21): 3897. doi:10.1016/0277-5387(96)00018 -6. ^ Brown, F.; Hall, G.R.; Walter, A.J. (1955). "The half-life of Cs137". Journal of Inorganic and Nuclear Chemistry 1 (4–5): 241–247. doi:10.1016/0022-1902(55)80027-9. ^ Sonzogni, Alejandro. "Interactive Chart of Nuclides". National Nuclear Data Center: Brookhaven National Laboratory. Retrieved 2008-06-06. ^ Ohki, Shigeo; Takaki, Naoyuki (14–16 October 2002). "Transmutation of Cesium-135 with Fast Reactors" (PDF). Seventh Information Exchange Meeting on Actinide and Fission Product Partitioning and Transmutation. Jeju, Korea. Retrieved 2010-09-26. ^ (PDF) CANDU Fundamentals (Report). CANDU Owners Group Inc.. Retrieved 2010-09-15. ^ Taylor, V. F.; Evans, R. D.; Cornett, R. J. (2008). "Preliminary evaluation of 135Cs/137Cs as a forensic tool for identifying source of radioactive contamination". Journal of Environmental Radioactivity 99 (1): 109–118. doi:10.1016/j.jenvrad.2007.07.006. PMID 17869392. ^ "Cesium | Radiation Protection". U.S. Environmental Protection Agency. 2006-06-28. Retrieved 2010-02-15. ^ Zerriffi, Hisham (2000-05-24). IEER Report: Transmutation – Nuclear Alchemy Gamble (Report). Institute for Energy and Environmental Research. Retrieved 2010-02-15. ^ (PDF) Chernobyl's Legacy: Health, Environmental and Socia-Economic Impacts and Recommendations to the Governments of Belarus, Russian Federation and Ukraine (Report). International Atomic Energy Agency. Retrieved 2010-02-18. ^ Kase, Takeshi; Konashi, Kenji; Takahashi, Hiroshi; Hirao, Yasuo (1993). "Transmutation of Cesium-137 Using Proton Accelerator". Journal of Nuclear Science and Technology 30 (9): 911–918. doi:10.3327/jnst.30.911. ^ "Magnetic susceptibility of the elements and inorganic compounds" (PDF). Handbook of Chemistry and Physics (81st ed.). CRC press. Retrieved 2010-09-26. ^ ""NIST Radionuclide Half-Life Measurements"". Retrieved 2011-03-13. ^ International Union of Pure and Applied Chemistry (2005). Nomenclature of Inorganic Chemistry (IUPAC Recommendations 2005). Cambridge (UK): RSC–IUPAC. ISBN 0-85404-438-8. pp. 248–49. Electronic version.. ^ Coghill, Anne M.; Garson, Lorrin R., eds (2006). The ACS Style Guide: Effective Communication of Scientific Information (3rd ed.). Washington, D.C.: American Chemical Society. p. 127. ISBN 0-8412-3999-1. ^ Coplen, T. B.; Peiser, H. S. (1998). "History of the recommended atomic-weight values from 1882 to 1997: a comparison of differences from current values to the estimated uncertainties of earlier values". Pure Appl. Chem. 70 (1): 237–257. doi:10.1351/pac199870010237. ^ "WebElements Periodic Table of the Elements". University of Sheffield. Retrieved 2010-12-01. ^ Butterman, William C.; Brooks, William E.; Reese, Jr., Robert G. (2004). "Mineral Commodity Profile: Cesium" (PDF). United States Geological Survey. Retrieved 2009-12- 27. ^ Heiserman, David L. (1992). Exploring Chemical Elements and their Compounds. McGraw -Hill. pp. 201–203. ISBN 0-8306-3015-5. ^ "Francium". Periodic.lanl.gov. Retrieved 2010-02-23. ^ Kaner, Richard (2003). "C&EN: It's Elemental: The Periodic Table – Cesium". American Chemical Society. Retrieved 2010-02- 25. ^ "Chemical Data – Caesium – Cs". Royal Society of Chemistry. Retrieved 2010-09-27. ^ Lynch, Charles T. (1974). CRC Handbook of Materials Science. CRC Press. p. 13. ISBN 978-0-8493-2321-8. Retrieved 2010-09-27. ^ Taova, T. M. et al. (June 22, 2003). "Density of melts of alkali metals and their Na-K-Cs and Na-K-Rb ternary systems" (PDF). Fifteenth symposium on thermophysical properties, Boulder, Colorado, USA. Retrieved 2010-09-26. ^ Deiseroth, H. J. (1997). "Alkali metal amalgams, a group of unusual alloys". Progress in Solid State Chemistry 25 (1–2): 73–123. doi:10.1016/S0079-6786(97)81004-7. ^ Greenwood, N.N.; Earnshaw, A. (1984). Chemistry of the Elements. Oxford, UK: Pergamon Press. ISBN 0-08-022057-6. ^ Wells, A.F. (1984). Structural Inorganic Chemistry (5 ed.). Oxford Science Publications. ISBN 0-19-855370-6. ^ Cotton, F. Albert; Wilkinson, G. (1962). Advanced Inorganic Chemistry. John Wiley & Sons, Inc.. p. 318. ISBN 0-471-84997-9. ^ Lide, David R., ed (2006). CRC Handbook of Chemistry and Physics (87th ed.). Boca Raton, FL: CRC Press. pp. 451, 514. ISBN 0-8493-0487 -3. ^ Tsai, Khi-Ruey; Harris, P. M.; Lassettre, E. N. (1956). "The Crystal Structure of Cesium Monoxide". Journal of Physical Chemistry 60 (3): 338–344. doi:10.1021/j150537a022. ^ "Information Bridge: DOE Scientific and Technical Information" (PDF). Office of Scientific and Technical Information — U.S. Department of Energy. 2009-11-23. Retrieved 2010-02-15. ^ Vol'nov, I. I.; Matveev, V. V. (1963). "Synthesis of cesium ozonide through cesium superoxide". Bulletin of the Academy of Sciences, USSR Division of Chemical Science 12 (6): 1040–1043. doi:10.1007/BF00845494. ^ Tokareva, S. A. (1971). "Alkali and Alkaline Earth Metal Ozonides". Russian Chemical Reviews 40 (2): 165–174. Bibcode 1971RuCRv..40..165T. doi:10.1070/RC1971v040n02ABEH001903. ^ Simon, A. (1997). "Group 1 and 2 Suboxides and Subnitrides — Metals with Atomic Size Holes and Tunnels". Coordination Chemistry Reviews 163: 253–270. doi:10.1016/S0010-8545 (97)00013-1. ^ Tsai, Khi-Ruey; Harris, P. M.; Lassettre, E. N. (1956). "The Crystal Structure of Tricesium Monoxide". Journal of Physical Chemistry 60 (3): 345–347. doi:10.1021/j150537a023. ^ Okamoto, H. (2009). "Cs-O (Cesium-Oxygen)". Journal of Phase Equilibria and Diffusion 31: 86. doi:10.1007/s11669-009-9636-5.