Cs

Cesium

Atomic Number 55 · Metal ampule in argon

The most electropositive stable element. Melts near body temperature. Used in atomic clocks that define the second.

Atomic Mass

132.91 u

Category

Alkali Metal

Phase (STP)

Solid

Density

1.873 g/cm³

Melting Point

28.44 °C

Boiling Point

671 °C

Electronegativity

0.79 (Pauling)

Atomic Radius

260 pm

Electron Configuration

[Xe] 6s1

Discovered

1860 — Robert Bunsen

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Sample form: Metal ampule in argon

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