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Chemical element with atomic number 55 (Cs)
Caesium, 55 Cs Pronunciation (SEE -zee-əm Alternative name cesium (US) Appearance pale gold
Atomic number (Z ) 55 Group group 1: hydrogen and alkali metals Period period 6 Block s-block Electron configuration [Xe ] 6s1 Electrons per shell 2, 8, 18, 18, 8, 1 Phase at STP solid Melting point 301.7 K (28.5 °C, 83.3 °F) Boiling point 944 K (671 °C, 1240 °F) Density (at 20° C) 1.886 g/cm3 [ 3] when liquid (at m.p. ) 1.843 g/cm3 Critical point 1938 K, 9.4 MPa[ 4] Heat of fusion 2.09 kJ/mol Heat of vaporization 63.9 kJ/mol Molar heat capacity 32.210 J/(mol·K) Vapor pressure
P (Pa)
1
10
100
1 k
10 k
100 k
at T (K)
418
469
534
623
750
940
Oxidation states common: +1 [ 5] Electronegativity Pauling scale: 0.79 Ionization energies 1st: 375.7 kJ/mol 2nd: 2234.3 kJ/mol 3rd: 3400 kJ/mol Atomic radius empirical: 265 pm Covalent radius 244±11 pm Van der Waals radius 343 pm Spectral lines of caesiumNatural occurrence primordial Crystal structure body-centered cubic (bcc) (cI2 ) Lattice constant a = 616.2 pm (at 20 °C)[ 3] Thermal expansion × 10−6 [ 3] Thermal conductivity 35.9 W/(m⋅K) Electrical resistivity 205 nΩ⋅m (at 20 °C) Magnetic ordering paramagnetic [ 6] Young's modulus 1.7 GPa Bulk modulus 1.6 GPa Mohs hardness 0.2 Brinell hardness 0.14 MPa CAS Number 7440-46-2 Naming from Latin caesius 'bluish grey', for its spectral colours Discovery Robert Bunsen and Gustav Kirchhoff (1860) First isolation Carl Setterberg (1882)
Category: Caesium references
^ "Standard Atomic Weights: Caesium" . CIAAW . 2013.^ Prohaska, Thomas; Irrgeher, Johanna; Benefield, Jacqueline; Böhlke, John K.; Chesson, Lesley A.; Coplen, Tyler B.; Ding, Tiping; Dunn, Philip J. H.; Gröning, Manfred; Holden, Norman E.; Meijer, Harro A. J. (2022-05-04). "Standard atomic weights of the elements 2021 (IUPAC Technical Report)" . Pure and Applied Chemistry . doi :10.1515/pac-2019-0603 . ISSN 1365-3075 . ^ a b c Arblaster, John W. (2018). Selected Values of the Crystallographic Properties of Elements . Materials Park, Ohio: ASM International. ISBN 978-1-62708-155-9 ^ Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics CRC Press . p. 4.121. ISBN 1-4398-5511-0 ^ Dye, J. L. (1979). "Compounds of Alkali Metal Anions". Angewandte Chemie International Edition 18 (8): 587–598. doi :10.1002/anie.197905871 . ^ "Magnetic susceptibility of the elements and inorganic compounds". Handbook of Chemistry and Physics (PDF) (87th ed.). CRC press. ISBN 0-8493-0487-3 . Retrieved 2010-09-26 . ^ Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF) . Chinese Physics C . 45 (3): 030001. doi :10.1088/1674-1137/abddae . ^ "NIST Radionuclide Half-Life Measurements" . NIST . Retrieved 2011-03-13 . 
