Rubidium is a chemical element ; it has symbol Rb and atomic number 37. It is a very soft, whitish-grey solid in the alkali metal group, similar to potassium and caesium .[8] Rubidium is the first alkali metal in the group to have a density higher than water . On Earth, natural rubidium comprises two isotopes : 72% is a stable isotope 85 Rb, and 28% is slightly radioactive 87 Rb, with a half-life of 48.8 billion years—more than three times as long as the estimated age of the universe .
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Rubidium, 37 Rb Pronunciation (roo-BID -ee-əm ) Appearance grey white
Atomic number (Z ) 37 Group group 1: hydrogen and alkali metals Period period 5 Block s-block Electron configuration [ Kr ] 5s1 Electrons per shell 2, 8, 18, 8, 1 Phase at STP solid Melting point 312.45 K (39.30 °C, 102.74 °F) Boiling point 961 K (688 °C, 1270 °F) Density (at 20° C) 1.534 g/cm3 [3] when liquid (at m.p. ) 1.46 g/cm3 Triple point 312.41 K, ? kPa[4] Critical point 2093 K, 16 MPa (extrapolated) [4] Heat of fusion 2.19 kJ/mol Heat of vaporization 69 kJ/mol Molar heat capacity 31.060 J/(mol·K) Vapor pressure
P (Pa)
1
10
100
1 k
10 k
100 k
at T (K)
434
486
552
641
769
958
Oxidation states −1, +1 (a strongly basic oxide) Electronegativity Pauling scale: 0.82 Ionization 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 Spectral lines of rubidiumNatural occurrence primordial Crystal structure body-centered cubic (bcc) (cI2 )Lattice constant a = 569.9 pm (at 20 °C)[3] Thermal expansion 85.6× 10−6 /K (at 20 °C)[3] Thermal conductivity 58.2 W/(m⋅K) Electrical resistivity 128 nΩ⋅m (at 20 °C) Magnetic ordering paramagnetic [5] Molar magnetic susceptibility +17.0× 10−6 cm3 /mol (303 K)[6] Young's modulus 2.4 GPa Bulk modulus 2.5 GPa Speed of sound thin rod 1300 m/s (at 20 °C) Mohs hardness 0.3 Brinell hardness 0.216 MPa CAS Number 7440-17-7 Discovery Robert Bunsen and Gustav Kirchhoff (1861)First isolation George de Hevesy
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German chemists Robert Bunsen and Gustav Kirchhoff discovered rubidium in 1861 by the newly developed technique, flame spectroscopy . The name comes from the Latin word rubidus , meaning deep red, the color of its emission spectrum. Rubidium's compounds have various chemical and electronic applications. Rubidium metal is easily vaporized and has a convenient spectral absorption range, making it a frequent target for laser manipulation of atoms .[9] Rubidium is not a known nutrient for any living organisms . However, rubidium ions have similar properties and the same charge as potassium ions, and are actively taken up and treated by animal cells in similar ways.