55
Cs
Cesium
132.90545196
Cesium (Cs)
Alkali MetalGroup 1Period 6s-block-block
Caesium or cesium is a chemical element with symbol Cs and atomic number 55. It is a soft, silvery-gold alkali metal with a melting point of 28 °C (82 °F), which makes it one of only five elemental metals that are liquid at or near room temperature. Caesium is an alkali metal and has physical and chemical properties similar to those of rubidium and potassium.
Latin name: Caesium
Atomic Number
55
Atomic Mass
132.90545196 g/mol
Phase (STP)
Solid
Electron Config.
[Xe] 6s¹
General
SymbolCs
Atomic Number55
Atomic Mass132.90545196 g/mol
CategoryAlkali Metal
Group1
Period6
Blocks-block
Electron Configuration[Xe] 6s¹
Valence Electrons1
Coloursilvery-gold metallic
Appearancesilvery gold
CAS NumberCAS7440-46-2
Physical Properties
Phase (STP)Solid
Density1.93 g/cm³
Melting Point28.44°C · 83.19°F · 301.59 K
Boiling Point670.85°C · 1239.53°F · 944.00 K
Atomic Properties
Atomic Radius298 pm
Electronegativity0.79 Pauling
Ionization Energy376 kJ/mol
Oxidation States+1
Ion ChargeCs+
Thermodynamic
Molar Heat32.21 J/(mol·K)
Crystal Structure
Crystal Structurebody-centered cubic
Mechanical Properties
Mohs Hardness0.2
Nuclear & Hazards
Half-lifestable
Abundance
In Universe0.00002%
In Sun0.000015%
In Earth's Crust0.00003%
In Oceans0.00004%
In Humans0.0000002%
Discovery & History
Discovery Year1860
Discovered ByRobert Bunsen, Gustav Kirchhoff
Country of DiscoveryGermany
Isotopes of Cesium
| Isotope | Abundance | Half-life | Decay |
|---|---|---|---|
| Cs-133 | 100% | Stable | — |
| Cs-134 | — | 2.0652 years | β⁻, EC |
| Cs-135 | — | 2.3 × 10⁶ years | β⁻ |
| Cs-137 | — | 30.17 years | β⁻ |