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Cesium (Cs)
Atomic number 55 · alkali
| Atomic number | 55 |
|---|---|
| Atomic mass | 132.90545 u |
| Molar mass | 132.90545 g/mol |
| Category | alkali |
| Group / period / block | 1 / 6 / s |
| Electron configuration | [Xe] 6s |
| Electrons per shell | 2, 8, 18, 18, 8, 1 |
| Electronegativity (Pauling) | 0.79 |
| Atomic radius | 260.0 pm |
| Density | 1.873 g/cm³ |
| First ionisation energy | 3.8939 eV |
| Melting point | 301.65 K (28.50 °C) |
| Boiling point | 944.15 K (671.00 °C) |
| Common oxidation states | +1 |
| Abundance in Earth's crust | 3 ppm |
Uses
Atomic clocks — they define the second
Discovery
1860, Gustov Kirchoff, Robert Bunsen