Cesium (Cs)

Cesium is a chemical element with symbol Cs and atomic number 55. It is a soft, silvery-golden alkali metal with a melting point of 28.5 °C, which makes it one of only five elemental metals that are liquid at or near room temperature.

Atomic Number

55

Atomic Mass

132.91 u

Category

alkali metal

Phase

solid

Density

1.93 g/cm³

Electron Shells

2, 8, 18, 18, 8, 1

Atomic Structure

Protons: 55 • Electrons: 55 • Neutrons: Varies by isotope

Electron Configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s¹

Discovery

1860 • Robert Bunsen, Gustav Kirchhoff