Rubidium, 37 General properties Pronunciation Template:Infobox element/pronunciation Appearance grey white Standard atomic weight (A r, standard ) Template:Infobox element/standard atomic weight Mass number Template:Infobox element/symbol-to-most-stable-isotope (most stable isotope)Rubidium in the periodic table Template:Infobox element/periodic table Atomic number (Z ) 37 Group Template:Infobox element/group Period period 5 Block s-block Element category Template:Infobox element/category format Electron configuration [Kr ] 5s1 Electrons per shell
2, 8, 18, 8, 1 Physical properties Phase at STP solid Melting point 312.45 K (39.30 °C, 102.74 °F) Boiling point 961 K (688 °C, 1270 °F) Density (near r.t. ) 1.532 g/cm3 when liquid (at m.p. ) 1.46 g/cm3 Triple point 312.41 K, ? kPa[1] Critical point 2093 K, 16 MPa (extrapolated) [1] Heat of fusion 2.19 kJ/mol [[Enthalpy of vaporization|Heat of Template:Engvar ]] 69 kJ/mol Molar heat capacity 31.060 J/(mol·K) [[Vapor pressure|Template:Engvar pressure Atomic properties Oxidation states Template:Infobox element/symbol-to-oxidation-state Electronegativity Pauling scale: 0.82 [[Ionization energy|Template:Engvar energies]] 1st: 403 kJ/mol 2nd: 2632.1 kJ/mol 3rd: 3859.4 kJ/mol Atomic radius empirical: 248 pm Covalent radius 220±9 pm Van der Waals radius 303 pm Template:Infobox element/spectral lines Other properties Crystal structure Template:Infobox element/crystal structure Speed of sound thin rod 1300 m/s (at 20 °C) Thermal expansion 90 µm/(m·K)[2] r.t. ) Thermal conductivity 58.2 W/(m·K) Electrical resistivity 128 nΩ·m (at 20 °C) Magnetic ordering paramagnetic [3] Magnetic susceptibility +17.0·10−6 cm3 /mol (303 K)[4] Young's modulus 2.4 GPa Bulk modulus 2.5 GPa Mohs hardness 0.3 Brinell hardness 0.216 MPa CAS Number 7440-17-7 History Discovery Robert Bunsen and Gustav Kirchhoff (1861) First isolation George de Hevesy Main isotopes of rubidium Template:Infobox element/isotopes table | references
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