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Pronunciation | (SEE-zee-əm) |
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Alternative name | cesium (US, informal) |
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Appearance | pale gold |
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Standard atomic weight (Ar, standard) | 132.90545196(6) |
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Atomic number (Z) | 55 |
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Group | group 1 (alkali metals) |
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Period | period 6 |
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Block | s-block |
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Element category | alkali metal |
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Electron configuration | [Xe] 6s1 |
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Electrons per shell | 2, 8, 18, 18, 8, 1 |
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Phase at STP | Cs: Solid |
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Melting point | 301.7 K (28.5 °C, 83.3 °F) |
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Boiling point | 944 K (671 °C, 1240 °F) |
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Density (near r.t.) | 1.93 g/cm3 |
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when liquid (at m.p.) | 1.843 g/cm3 |
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Critical point | 1938 K, 9.4 MPa |
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Heat of fusion | 2.09 kJ/mol |
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Heat of vaporization | 63.9 kJ/mol |
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Molar heat capacity | 32.210 J/(mol·K) |
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Vapor pressureP (Pa) | 1 | 10 | 100 | 1 k | 10 k | 100 k |
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at T (K) | 418 | 469 | 534 | 623 | 750 | 940 |
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Oxidation states | −1, +1 (a strongly basic oxide) |
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Electronegativity | Pauling scale: 0.79 |
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Ionization energies | - 1st: 375.7 kJ/mol
- 2nd: 2234.3 kJ/mol
- 3rd: 3400 kJ/mol
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Atomic radius | empirical: 265 pm |
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Covalent radius | 244±11 pm |
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Van der Waals radius | 343 pm |
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Spectral lines of caesium |
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Natural occurrence | Cs: Primordial |
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Crystal structure | body-centered cubic (bcc) |
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Thermal expansion | 97 µm/(m·K) (at 25 °C) |
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Thermal conductivity | 35.9 W/(m·K) |
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Electrical resistivity | 205 nΩ·m (at 20 °C) |
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Magnetic ordering | paramagnetic |
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Young's modulus | 1.7 GPa |
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Bulk modulus | 1.6 GPa |
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Mohs hardness | 0.2 |
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Brinell hardness | 0.14 MPa |
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CAS Number | 7440-46-2 |
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Naming | from Latin caesius, sky blue, for its spectral colours |
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Discovery | Robert Bunsen and Gustav Kirchhoff (1860) |
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First isolation | Carl Setterberg (1882) |
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| references |