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| Caesium | Césium | Cezij | Cesio | Cäsium | ||||||||||||||||||||
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Cs Caesium |
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- Caesium was discovered by Robert Bunsen and Gustav Kirchhoff (Germany) in 1860. The origin of the name comes from the Latin word caesius meaning sky blue or heavenly blue. It is very soft, light grey, ductile metal. Reacts readily with oxygen. Reacts explosively with water.
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ALKALI METAL | |
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| Relative atomic mass: | 132.90545(2) | Electronic configuration: | [Xe] 6s1 |
| Formal oxidation number: | +1 | Electronegativities: | 0.79 |
| Thermal conductivity: | 35.9 W m-1 K-1 | Electrical resistivity (20 °C): | 20 μΩcm |
| Atomic radius: | 265.5 pm | Standard state (20 °C): | solid |
| Density (g dm-3): | 1873 (293 K) 1843 (m.p.) |
Molar volume (cm3 mol-1): | 70.96 (293 K) 72.11 (m.p.) |
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THERMAL PROPERTIES | |
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| Melting point: | 798 °C | Heat of fusion: | 2.09 kJ mol-1 |
| Boiling point: | 3443 °C | Heat of vaporization: | 66.5 kJ mol-1 |
| Critical temperature: | 1784 °C | Heat of atomization: | 77.58 kJ mol-1 |
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IONIZATION ENERGIES AND ABUNDANCE | |
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| 1st ionization energy: | 375.71 kJ mol-1 | Abundance of element (air): | - ppm |
| 2nd ionization energy: | 2234.37 kJ mol-1 | Abundance of element (Earth's crust): | 1 ppm |
| 3rd ionization energy: | - kJ mol-1 | Abundance of element (oceans): | 0.0005 ppm |
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ISOTOPES | |
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Isotopes | Relative atomic mass | Abundance (%) |
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133Cs | 132.905447(3) | 100 |
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MINERALS AND USES | |
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- Caesium is found in pollucite [(Cs4Al4Si9O26).H2O] and as trace in lepidolite. Used as a 'getter' to remove air traces in vacuum and cathode-ray tubes. Also used in producing photoelectric devices and atomic clocks. Since it ionises readily, it is used as an ion rocket motor propellant. The price of 99.8 % pure cesium metal is 461.80 € for 50 g.
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REDUCTION POTENTIALS | |
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Balanced half-reaction | Eo / V | Annotation |
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Cs+ + e-  Cs(s) |
- 2.91 | |
