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Information valid for Cs-133 unless otherwise noted

Basic Information

Symbol: Cs
Atomic Number: 55
Mass: 132.90546
Melting Point: 28.5 C
Boiling Point: 678.4 C
Number of Protons/Electrons: 55
Number of Neutrons: 78
Classification: Alkali Metal
Crystal Structure: Cubic
Density @ 293 K: 1.873 g/cm3
Color: silver
British Spelling: Caesium
IUPAC Spelling: Caesium

Atomic Structure

[Bohr Model of Cesium]
Number of Energy Levels: 6

  1. First Energy Level: 2
    Second Energy Level: 8
    Third Energy Level: 18
    Fourth Energy Level: 18
    Fifth Energy Level: 8
    Sixth Energy Level: 1


Isotope Half Life
Cs-126 1.6 minutes
Cs-129 1.3 days
Cs-131 9.7 days
Cs-132 6.4 days
Cs-133 Stable
Cs-134 2.1 years
Cs-134m 2.9 hours
Cs-135 2300000.0 years
Cs-136 13.2 days
Cs-137 30.2 years
Cs-138 32.2 minutes
Cs-139 9.3 minutes


Date of Discovery: 1860
Discoverer: Fustov Kirchoff
Name Origin: From the Latin word caesius (sky blue)
Uses: removes air traces in vacuum tubes
Obtained From: pollucite, lepidolite