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Pronunciation | (roo-BID-ee-əm) |
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Appearance | grey white |
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| 85.4678(3)[1] |
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Atomic number (Z) | 37 |
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Group | group 1: hydrogen and alkali metals |
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Period | period 5 |
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Block | s-block |
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Electron configuration | [Kr] 5s1 |
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Electrons per shell | 2, 8, 18, 8, 1 |
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Phase at STP | solid |
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Melting point | 312.45 K (39.30 °C, 102.74 °F) |
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Boiling point | 961 K (688 °C, 1270 °F) |
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Density (near r.t.) | 1.532 g/cm3 |
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when liquid (at m.p.) | 1.46 g/cm3 |
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Triple point | 312.41 K, ? kPa[2] |
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Critical point | 2093 K, 16 MPa (extrapolated)[2] |
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Heat of fusion | 2.19 kJ/mol |
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Heat of vaporization | 69 kJ/mol |
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Molar heat capacity | 31.060 J/(mol·K) |
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Vapor pressure
P (Pa) |
1 |
10 |
100 |
1 k |
10 k |
100 k |
at T (K) |
434 |
486 |
552 |
641 |
769 |
958 |
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Oxidation states | −1, +1 (a strongly basic oxide) |
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Electronegativity | Pauling scale: 0.82 |
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Ionization energies | - 1st: 403 kJ/mol
- 2nd: 2632.1 kJ/mol
- 3rd: 3859.4 kJ/mol
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Atomic radius | empirical: 248 pm |
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Covalent radius | 220±9 pm |
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Van der Waals radius | 303 pm |
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Spectral lines of rubidium |
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Natural occurrence | primordial |
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Crystal structure | body-centered cubic (bcc) |
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Speed of sound thin rod | 1300 m/s (at 20 °C) |
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Thermal expansion | 90 µm/(m⋅K)[3] (at r.t.) |
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Thermal conductivity | 58.2 W/(m⋅K) |
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Electrical resistivity | 128 nΩ⋅m (at 20 °C) |
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Magnetic ordering | paramagnetic[4] |
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Molar magnetic susceptibility | +17.0×10−6 cm3/mol (303 K)[5] |
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Young's modulus | 2.4 GPa |
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Bulk modulus | 2.5 GPa |
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Mohs hardness | 0.3 |
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Brinell hardness | 0.216 MPa |
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CAS Number | 7440-17-7 |
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Discovery | Robert Bunsen and Gustav Kirchhoff (1861) |
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First isolation | George de Hevesy |
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Main isotopes[6] |
Decay |
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abundance |
half-life (t1/2) |
mode |
product |
82Rb |
synth |
1.2575 m |
β+ |
82Kr |
83Rb |
synth |
86.2 d |
ε |
83Kr |
γ |
– |
84Rb |
synth |
32.9 d |
ε |
84Kr |
β+ |
84Kr |
γ |
– |
β− |
84Sr |
85Rb |
72.2% |
stable |
86Rb |
synth |
18.7 d |
β− |
86Sr |
γ |
– |
87Rb |
27.8% |
4.97×1010 y |
β− |
87Sr |
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Category: Rubidium | references |