55
Cs
132.91
Caesium (Cs)
Element 55 · Period 6 · Group 1
alkali-metal
solid at room temp
s-block
About Caesium
Most electropositive metal. Used in atomic clocks — defines the SI second.
Physical Properties
Atomic Mass
132.91 u
State at 25°C
Solid
Melting Point
28.44 °C
Boiling Point
671 °C
Density
1.879 g/cm³
Magnetism
Paramagnetic
Atomic Properties
Electron Configuration
[Xe] 6s¹
Electron Shells
2, 8, 18, 18, 8, 1
Electronegativity
0.79
Atomic Radius
298 pm
Ionization Energy
376 kJ/mol
Oxidation States
+1
Discovery & History
Discovered By
Robert Bunsen
Discovery Year
1860
Named By
Robert Bunsen
Name origin: Latin: caesius (sky blue)
Frequently Asked Questions
- Is Caesium a metal, nonmetal, or metalloid?
- Caesium is classified as a alkali-metal.
- What state is Caesium in at room temperature?
- Caesium is a solid at standard room temperature (25°C).
- What is the atomic mass of Caesium?
- Caesium has an atomic mass of 132.91 atomic mass units (u).
- Who discovered Caesium?
- Caesium was discovered by Robert Bunsen in 1860.
- Where is Caesium on the periodic table?
- Caesium is element number 55, located in period 6 and group 1.