Cesium Element Facts

General
States
Energies
Oxidation & Electrons
Appearance & Characteristics
Reactions & Compounds
Radius
Conductivity
Abundance & Isotopes

55 Cs 132.9054 Cesium

Cesium atomic clock. Accurate to 1 second in 60 million years.
(Photo: NASA)

Name: Cesium
Type: Alkali Metal
Density @ 293 K: 1.873 g/cm³

Discovery of Cesium
Cesium was discovered by Robert Bunsen and Gustav Kirchhoff in 1860, when they analyzed the spectrum of mineral water.

Cesium was the first element discovered using a spectroscope. A year earlier, Bunsen and Kirchhoff had developed a spectroscope that could examine the colored flame of substances in detail by looking at their emission spectra through a prism. When studying the spectrum of the residue from some spa mineral water, they found a series of emission spectra lines that did not correspond to any known element.

Bunsen and Kirchhoff named the element cesium, from the Latin word 'caesius', meaning sky blue, after the blue lines they saw in the spectrum.

The Latin spelling is still reflected in British English where cesium is spelt 'caesium'.

In 1861 Bunsen and Kirchhoff also discovered rubidium by the same method.

Symbol: Cs
Atomic weight: 132.9055
Atomic volume: 71.07 cm³/mol

State (s, l, g): solid
Melting point: 301.6 K   (28.4 ^oC)

Boiling point: 943.2 K   (670 ^oC)

Specific heat capacity: 0.24 J g^-1 K^-1
Heat of fusion: 2.092 kJ mol^-1
1^st ionization energy: 375.7 kJ mol^-1
3^rd ionization energy: 3400 kJ mol^-1

Heat of atomization: 76 kJ mol^-1
Heat of vaporization : 67.740 kJ mol^-1
2^nd ionization energy: 2234.3 kJ mol^-1
Electron affinity: 45.506 kJ mol^-1

Shells: 2,8,18,18,8,1
Minimum oxidation number: 0
Min. common oxidation no.: 0
Electronegativity (Pauling Scale): 0.79

Electron configuration: [Xe] 6s¹
Maximum oxidation number: 3
Max. common oxidation no.: 3
Polarizability volume: 59.6 ų

Structure: bcc: body-centered cubic
Hardness: 0.2 mohs

Color: yellow/silvery


Harmful effects:
Cesium must be kept under an inert liquid/gas or in a vacuum to protect it from air and water. Cesium compounds are considered to be mildy toxic.

Characteristics:
Cesium is silvery-gold, soft, ductile alkali metal. It is liquid in a warm room, melting at 28.4 ^oC (83.1 ^oF).

Cesium is one of the few metals that is liquid near room temperature. The others are gallium, francium and mercury.

Cesium is an extremely reactive metal and the most alkaline of the elements. It reacts explosively upon contact with water producing cesium hydroxide (CsOH), an extremely strong base that can rapidly corrode glass.

Uses:
Cesium is used in atomic clocks, which are incredibly accurate. NIST-F1, America's primary time and frequency standard, is a cesium fountain atomic clock developed at the NIST laboratories in Boulder, Colorado. NIST-F1 contributes to the international group of atomic clocks that define Coordinated Universal Time (UTC), the official world time. As scientists continue to improve its technology, uncertainty in NIST-F1's measurement of time is continually improving. Currently it neither gains nor loses as much a second in more than 60 million years - but see strontium.

Cesium is also used in photoelectric cells and as a catalyst in the hydrogenation of organic compounds. The metal is used as a 'getter' in vacuum tubes.

Cesium hydroxide is used to etch silicon.

Reaction with air: vigorous, ⇒ Cs₂O
Reaction with 15 M HNO₃: vigorous, ⇒ CsNO₃
Oxide(s): Cs₂O, Cs2, Cs₂O₂
Hydride(s): CsH

Reaction with 6 M HCl: vigorous, ⇒ H₂, CsCl
Reaction with 6 M NaOH: vigorous, ⇒ H₂, CsOH
Chloride(s): CsCl

Atomic radius: 260 pm
Ionic radius (2+ ion): pm
Ionic radius (2- ion): pm

Ionic radius (1+ ion): 181 pm
Ionic radius (3+ ion): pm
Ionic radius (1- ion): pm

Thermal conductivity: 35.9 W m^-1 K^-1

Electrical conductivity: 5.3 x 10⁶ S m^-1