55Cs132.905
Alkali Metals-block
Cesium
Element 55 on the periodic table, symbol Cs, group 1, period 6.
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.
Appearance: silvery gold
Properties
- Atomic Number
- 55
- Atomic Mass
- 132.9055 u
- Group
- 1
- Period
- 6
- Block
- s-block
- Category
- Alkali Metal
- State at 25 °C
- Solid
- Melting Point
- 301.7 K · 28.6 °C
- Boiling Point
- 944 K · 670.9 °C
- Density
- 1.93 g/cm³
- Atomic Radius
- 260 pm
- Electronegativity
- 0.79
- Oxidation States
- +1
- Abundance in Crust
- 3 mg/kg
- Discovered
- 1860
- Discovered By
- Robert Bunsen
Electron Configuration
[Xe] 6s1
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s1
Ionisation Energies (kJ/mol)
- 1. 375.7
- 2. 2,234.3
- 3. 3,400
Elements near Cesium
Elements in the same group share the number of outer electrons and behave in similar ways. Elements in the same period share a shell, so they change steadily from left to right.