055Alkali metal · Group 1 · Period 6
Cesium
Cesium (Cs) is element 55, a alkali metal in the s-block — group 1, period 6. It is a solid at room temperature with 6 electron shells (2, 8, 18, 18, 8, 1) and an atomic mass of 132.905451966 u.
- Atomic mass
- 132.9 u
- Phase · STP
- solid
- Melting
- 302 K · 29 °C
- Boiling
- 944 K · 671 °C
- Electronegativity
- 0.79
- Density
- 1.93 g/cm³
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Identity
- Atomic number
- 55
- Standard atomic weight
- 132.9 u
- Category
- Alkali metal
- Group
- 1 · Alkali metals
- Period
- 6
- Block
- s-block
- Oxidation states
- +1
Physical properties
- Melting point
- 302 K · 29 °C
- Boiling point
- 944 K · 671 °C
- Density
- 1.93 g/cm³
- Molar heat capacity
- 32.21 J/(mol·K)
- Atomic radius
- 343 pm
- Electron affinity
- 45.505 kJ/mol
Atomic structure
55protons
78neutrons
55electrons
1valence e⁻
- Noble-gas notation
- [Xe] 6s1
- Full configuration
- 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s1
- Electrons per shell
- 2, 8, 18, 18, 8, 1
Periodic trends
Where Cesium ranks across all 118 elements.
Ionization energies
Energy to remove each successive electron (kJ/mol).
375.71
2.2k2
3.4k3
Successive ionization energies (kJ/mol, log scale).
Discovery
- Discovered
- 1860
- Discovered by
- Robert Bunsen
- Named by
- —
- Appearance
- silvery gold