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Cs 55

Cesium (Cs)

alkali-metal
Period: 6 Group: 1 Block: s

Solid

Standard Atomic Weight

132.905452 u

Electron configuration

[Xe] 6s1

Melting point

28.44 °C (301.59 K)

Boiling point

670.85 °C (944 K)

Density

1930 kg/m³

Oxidation states

−1, +1

Electronegativity (Pauling)

0.79

Ionization energy (1st)

Discovery year

1860

Atomic radius

260 pm

Details

Name origin Latin: coesius (sky blue); for the blue lines of its spectrum.
Discovery country Germany
Discoverers Gustov Kirchoff, Robert Bunsen

Cesium is a soft alkali metal with very low ionization energy and an unusually low melting point for a metal. It occurs naturally as the single stable isotope ¹³³Cs, chiefly in rare granitic pegmatite minerals. Chemically it is the heaviest stable group 1 element and forms almost exclusively Cs⁺ salts. Its best-known technological role is in the definition of the second, based on the microwave transition of the ¹³³Cs atom.

The metal is characterized by a spectrum containing two bright lines in the blue along with several others in the red, yellow, and green wavelengths. It is silvery white, soft, and ductile. It is the most electropositive and most alkaline element.

Cesium, gallium, and mercury are the only three metals that are liquid at room temperature. Cesium reacts explosively with cold water, and reacts with ice at temperatures above -116C. Cesium hydroxide, the strongest base known, attacks glass.

The name derives from the Latin caesius for "sky blue", which was the colour of the caesium line in the spectroscope. Caesium was discovered by the German chemist Robert Wilhelm Bunsen and the German physicist Gustav Robert Kirchhoff in 1860. It was first isolated by the German chemist Carl Setterberg in 1882.

Cesium was discovered by Robert Wilhelm Bunsen and Gustav Robert Kirchhoff, German chemists, in 1860 through the spectroscopic analysis of Durkheim mineral water. They named cesium after the blue lines they observed in its spectrum. Today, cesium is primarily obtained from the mineral pollucite (CsAlSi2O6). Obtaining pure cesium is difficult since cesium ores are frequently contaminated with rubidium, an element that is chemically similar to cesium. To obtain pure cesium, cesium and rubidium ores are crushed and heated with sodium metal to 650°C, forming an alloy that can then be separated with a process known as fractional distillation. Metallic cesium is too reactive to easily handle and is usually sold in the form of cesium azide (CsN3). Cesium is recovered from cesium azide by heating it.

From the Latin word caesius, sky blue. Cesium was discovered spectroscopically in 1860 by Bunsen and Kirchhoff in mineral water from Durkheim.

Read about Cesium on Wikipedia

Images

Properties

Physical

Atomic radius (empirical) 260 pm
Covalent radius 244 pm
Van der Waals radius 343 pm
Metallic radius 235 pm
Density
Molar volume 0.07 L/mol
Phase at STP solid
Melting point 28.44 °C
Boiling point 670.85 °C
Thermal conductivity 35.9 W/(m·K)
Specific heat capacity 0.242 J/(g·K)
Molar heat capacity 32.21 J/(mol·K)
Crystal structure bcc

Chemical

Electronegativity (Pauling) 0.79
Electronegativity (Allen) 0.659
Electron affinity
Ionization energy (1st)
Ionization energy (2nd)
Ionization energy (3rd)
Ionization energy (4th)
Ionization energy (5th)
Oxidation states −1, +1
Valence electrons 1
Electron configuration
Electron configuration (semantic)

Thermodynamic

Critical point (temperature) 1665 °C
Critical point (pressure) 9.400000e+6 Pa
Heat of fusion 0.0216614 eV
Heat of vaporization 0.67367985 eV
Heat of sublimation 0.79286936 eV
Heat of atomization 0.79286936 eV
Atomization enthalpy

Nuclear

Stable isotopes 1
Discovery year 1860

Abundance

Abundance (Earth's crust) 3 mg/kg
Abundance (ocean)

Reactivity

N/A

Crystal Structure

Lattice constant a 605 pm

Electronic Structure

Electrons per shell 2, 8, 18, 18, 8, 1

Identifiers

CAS number 7440-46-2
Term symbol
InChI InChI=1S/Cs
InChI Key TVFDJXOCXUVLDH-UHFFFAOYSA-N

Electron Configuration Measured

Ion charge
Protons 55
Electrons 55
Charge Neutral
Configuration Cs: 6s¹
Electron configuration
Measured
[Xe] 6s¹
1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ 6s¹
Orbital diagram
1s
2/2
2s
2/2
2p
6/6
3s
2/2
3p
6/6
4s
2/2
3d
10/10
4p
6/6
5s
2/2
4d
10/10
5p
6/6
6s
1/2 1↑
Total electrons: 55 Unpaired: 1 ?

Atomic model

Protons 55
Neutrons 78
Electrons 55
Mass number 133
Stability Stable

Isotopes change neutron count, mass, and stability — not the electron configuration of a neutral atom.

Schematic atomic model, not to scale.

Atomic Fingerprint

Emission / Absorption Spectrum

25 / 50 (50 with intensity)
Measured
Emission Visible: 380–750 nm
Source: NIST Atomic Spectra Database Wavelengths in air

Isotope Distribution

Monoisotopic element
Only naturally occurring isotope: 133 — 100.0000%
133100.0000%Mass numberNatural abundance (%)
Mass numberAtomic mass (u)Natural abundanceHalf-life
133 Stable132.905451961 ± 0.000000008100.0000%Stable
Measured

Phase / State

1 atm / 101.325 kPa
Solid 25 °C (298.15 K)

Reason: 3.4 °C below melting point (28.44 °C)

Melting point 28.44 °C
Boiling point 670.85 °C
Below melting by 3.4 °C
0 K Current temperature: 25 °C 6000 K
Phase timeline

Schematic, not to scale

Solid
Liquid
Gas
Melting
Boiling
25°C
Solid
Liquid
Gas
Current

Phase transition points

Melting point Literature
28.44 °C
Boiling point Literature
670.85 °C
Current phase Calculated
Solid

Transition energies

Heat of fusion Literature
0.0216614 eV

Energy required to melt 1 mol at melting point

Heat of vaporization Literature
0.67367985 eV

Energy required to vaporize 1 mol at boiling point

Heat of sublimation Literature
0.79286936 eV

Energy required to sublime 1 mol at sublimation point

Density

Reference density Literature
1930 kg/m³

At standard conditions

Current density Calculated
1930 kg/m³

At standard conditions

Advanced

Critical point Literature
1665 °C

Atomic Spectra

Showing 10 of 55 Atomic Spectra. Sorted by ion charge (ascending).

Lines Holdings ?

IonChargeTotal linesTransition probabilitiesLevel designations
Cs I 023042228
Cs II +1175721737
Cs III +2101010101010
Cs IV +32070207
Cs V +41430143
Cs VI +567067
Cs VII +61850185
Cs VIII +711113111
Cs IX +8501650
Cs X +9868686
NIST Lines Holdings →

Levels Holdings ?

IonChargeLevels
Cs I 0179
Cs II +1316
Cs III +2174
Cs IV +3116
Cs V +450
Cs VI +532
Cs VII +679
Cs VIII +755
Cs IX +869
Cs X +979
NIST Levels Holdings →
55 Cs 132.90545196

Cesium — Atomic Orbital Visualizer

[Xe]6s1
Energy levels 2 8 18 18 8 1
Oxidation states -1, +1
HOMO 6s n=6 · l=0 · m=0
Cesium — Atomic Orbital Visualizer Preview
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55 Cs 132.90545196

Cesium — Crystal Structure Visualizer

Body-Centered Cubic · Pearson cI2
Experimental
Pearson cI2
Coord. № 8
Packing 68.000%
Cesium — Crystal Structure Visualizer Preview
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Ionic Radii

ChargeCoordinationSpinRadius
+16N/A167 pm
+18N/A174 pm
+19N/A178 pm
+110N/A181 pm
+111N/A185 pm
+112N/A188 pm

Compounds

Cs
132.905 u
Cs
136.907 u
Cs+
132.905 u
Cs
130.905 u
Cs
133.907 u
Cs
134.906 u
Cs
128.906 u
Cs
143.932 u
Cs
131.906 u
Cs
135.907 u
Cs
126.907 u
Cs
124.910 u
Cs
137.911 u
Cs
129.907 u
Cs
138.913 u
Cs+
136.907 u
Cs
142.927 u
Cs
140.920 u
Cs+
133.907 u
Cs+
131.906 u
Cs+
130.905 u

Isotopes (1)

Cesium has more isotopes than any element32with masses ranging from 114 to 145.

Mass numberAtomic mass (u)Natural abundanceHalf-lifeDecay mode
133 Stable132.905451961 ± 0.000000008100.0000%Stable
stable
133 Stable
Atomic mass (u) 132.905451961 ± 0.000000008
Natural abundance 100.0000%
Half-life Stable
Decay mode
stable

Spectral Lines

Showing 50 of 728 Spectral Lines. Only spectral lines with measured intensity are shown by default.

Wavelength (nm)IntensityIon stageTypeTransitionAccuracySource
460.37908 nm10000000Cs IIemission5p5.(2P*<3/2>).6s 2[3/2]* → 5p5.(2P*<3/2>).6p 2[5/2]MeasuredNIST
522.70372 nm7500000Cs IIemission5p5.(2P*<3/2>).6s 2[3/2]* → 5p5.(2P*<3/2>).6p 2[1/2]MeasuredNIST
592.56312 nm5100000Cs IIemission5p5.(2P*<3/2>).5d 2[7/2]* → 5p5.(2P*<3/2>).6p 2[5/2]MeasuredNIST
556.3024 nm3900000Cs IIemission5p5.(2P*<3/2>).5d 2[3/2]* → 5p5.(2P*<3/2>).6p 2[3/2]MeasuredNIST
495.28523 nm3700000Cs IIemission5p5.(2P*<3/2>).5d 2[1/2]* → 5p5.(2P*<3/2>).6p 2[5/2]MeasuredNIST
695.54998 nm3700000Cs IIemission5p5.(2P*<3/2>).5d 2[7/2]* → 5p5.(2P*<3/2>).6p 2[5/2]MeasuredNIST
524.93849 nm2900000Cs IIemission5p5.(2P*<3/2>).6s 2[3/2]* → 5p5.(2P*<3/2>).6p 2[3/2]MeasuredNIST
504.38026 nm2700000Cs IIemission5p5.(2P*<3/2>).6s 2[3/2]* → 5p5.(2P*<3/2>).6p 2[3/2]MeasuredNIST
483.01864 nm2500000Cs IIemission5p5.(2P*<3/2>).6s 2[3/2]* → 5p5.(2P*<3/2>).6p 2[5/2]MeasuredNIST
583.11404 nm2400000Cs IIemission5p5.(2P*<3/2>).6s 2[3/2]* → 5p5.(2P*<3/2>).6p 2[5/2]MeasuredNIST
537.09876 nm2200000Cs IIemission5p5.(2P*<3/2>).5d 2[1/2]* → 5p5.(2P*<3/2>).6p 2[1/2]MeasuredNIST
452.67416 nm2000000Cs IIemission5p5.(2P*<3/2>).5d 2[1/2]* → 5p5.(2P*<3/2>).6p 2[3/2]MeasuredNIST
487.00392 nm1900000Cs IIemission5p5.(2P*<1/2>).6s 2[1/2]* → 5p5.(2P*<1/2>).6p 2[3/2]MeasuredNIST
427.71303 nm1800000Cs IIemission5p5.(2P*<3/2>).6s 2[3/2]* → 5p5.(2P*<3/2>).6p 2[3/2]MeasuredNIST
697.96684 nm1600000Cs IIemission5p5.(2P*<3/2>).5d 2[5/2]* → 5p5.(2P*<3/2>).6p 2[3/2]MeasuredNIST
426.470255 nm1400000Cs IIemission5p5.(2P*<3/2>).6p 2[5/2] → 5p5.(2P*<3/2>).6d 2[7/2]*MeasuredNIST
721.9603 nm1400000Cs IIIemission5s2.5p5 2P* → 5s2.5p5 2P*MeasuredNIST
714.95415 nm1300000Cs IIemission5p5.(2P*<1/2>).5d 2[5/2]* → 5p5.(2P*<1/2>).6p 2[3/2]MeasuredNIST
450.15517 nm1200000Cs IIemission5p5.(2P*<3/2>).6s 2[3/2]* → 5p5.(2P*<3/2>).6p 2[1/2]MeasuredNIST
527.40539 nm1100000Cs IIemission5p5.(2P*<3/2>).5d 2[1/2]* → 5p5.(2P*<3/2>).6p 2[1/2]MeasuredNIST
534.91319 nm1000000Cs IIemission5p5.(2P*<1/2>).6s 2[1/2]* → 5p5.(2P*<1/2>).6p 2[3/2]MeasuredNIST
653.6445 nm1000000Cs IIemission5p5.(2P*<3/2>).5d 2[3/2]* → 5p5.(2P*<3/2>).6p 2[5/2]MeasuredNIST
612.86072 nm980000Cs IIemission5p5.(2P*<3/2>).5d 2[3/2]* → 5p5.(2P*<3/2>).6p 2[5/2]MeasuredNIST
672.44659 nm960000Cs IIemission5p5.(2P*<1/2>).5d 2[5/2]* → 5p5.(2P*<1/2>).6p 2[3/2]MeasuredNIST
664.65663 nm880000Cs IIemission5p5.(2P*<1/2>).5d 2[3/2]* → 5p5.(2P*<1/2>).6p 2[1/2]MeasuredNIST
400.65447 nm860000Cs IIIemission5s2.5p4.(3P<2>).6s 2[2] → 5s2.5p4.(3P<2>).6p 2[3]*MeasuredNIST
649.55329 nm830000Cs IIemission5p5.(2P*<3/2>).5d 2[7/2]* → 5p5.(2P*<3/2>).6p 2[5/2]MeasuredNIST
497.25963 nm820000Cs IIemission5p5.(2P*<3/2>).6p 2[5/2] → 5p5.(2P*<3/2>).7s 2[3/2]*MeasuredNIST
403.985602 nm800000Cs IIemission5p5.(2P*<3/2>).6p 2[5/2] → 5p5.(2P*<3/2>).6d 2[7/2]*MeasuredNIST
436.329875 nm760000Cs IIemission5p5.(2P*<3/2>).6p 2[3/2] → 5p5.(2P*<3/2>).6d 2[5/2]*MeasuredNIST
388.83763 nm740000Cs IIIemission5s2.5p4.(3P<1>).5d 2[3] → 5s2.5p4.(3P<2>).6p 2[3]*MeasuredNIST
441.02226 nm720000Cs IIIemission5s2.5p4.(3P<2>).5d 2[3] → 5s2.5p4.(3P<2>).6p 2[2]*MeasuredNIST
450.67197 nm720000Cs IIIemission5s2.5p4.(3P<2>).5d 2[3] → 5s2.5p4.(3P<2>).6p 2[2]*MeasuredNIST
476.36362 nm700000Cs IIemission5p5.(2P*<1/2>).6s 2[1/2]* → 5p5.(2P*<1/2>).6p 2[1/2]MeasuredNIST
520.95813 nm650000Cs IIemission5p5.(2P*<1/2>).6s 2[1/2]* → 5p5.(2P*<1/2>).6p 2[3/2]MeasuredNIST
392.55957 nm620000Cs IIIemission5s2.5p4.(3P<2>).5d 2[3] → 5s2.5p4.(3P<2>).6p 2[3]*MeasuredNIST
442.56759 nm560000Cs IIIemission5s2.5p4.(3P<2>).6s 2[2] → 5s2.5p4.(3P<2>).6p 2[2]*MeasuredNIST
428.837507 nm510000Cs IIemission5p5.(2P*<3/2>).6p 2[3/2] → 5p5.(2P*<3/2>).6d 2[5/2]*MeasuredNIST
488.00516 nm490000Cs IIemission5p5.(2P*<1/2>).6s 2[1/2]* → 5p5.(2P*<1/2>).6p 2[1/2]MeasuredNIST
581.41641 nm450000Cs IIemission5p5.(2P*<3/2>).5d 2[3/2]* → 5p5.(2P*<3/2>).6p 2[3/2]MeasuredNIST
395.95055 nm420000Cs IIemission5p5.(2P*<3/2>).5d 2[1/2]* → 5p5.(2P*<3/2>).6p 2[1/2]MeasuredNIST
461.61693 nm420000Cs IIemission5p5.(2P*<1/2>).6s 2[1/2]* → 5p5.(2P*<1/2>).6p 2[1/2]MeasuredNIST
453.896566 nm410000Cs IIemission5p5.(2P*<3/2>).6p 2[3/2] → 5p5.(2P*<3/2>).6d 2[3/2]*MeasuredNIST
440.525568 nm390000Cs IIemission5p5.(2P*<3/2>).6p 2[1/2] → 5p5.(2P*<3/2>).7s 2[3/2]*MeasuredNIST
437.30356 nm370000Cs IIemission5p5.(2P*<3/2>).5d 2[1/2]* → 5p5.(2P*<3/2>).6p 2[3/2]MeasuredNIST
452.28578 nm350000Cs IIIemission5s2.5p4.(3P<2>).6s 2[2] → 5s2.5p4.(3P<2>).6p 2[2]*MeasuredNIST
389.698641 nm340000Cs IIemission5p5.(2P*<3/2>).6p 2[1/2] → 5p5.(2P*<3/2>).6d 2[1/2]*MeasuredNIST
404.34262 nm310000Cs IIIemission5s2.5p4.(1D<2>).6s 2[2] → 5s2.5p4.(1D<2>).6p 2[3]*MeasuredNIST
645.6318 nm310000Cs IIIemission5s2.5p4.(3P<2>).7p 2[3]* → 5s2.5p4.(3P<2>).7d 2[4]MeasuredNIST
607.9854 nm300000Cs IIIemission5s2.5p4.(3P<2>).5f 2[2]* → 5s2.5p4.(3P<2>).5g 2[3]MeasuredNIST

Extended Properties

Covalent Radii (Extended)

Covalent radius (Pyykkö)  
Covalent radius (Pyykkö, double)  
Covalent radius (Bragg)  

Van der Waals Radii

Truhlar  
Batsanov  
Alvarez  
UFF  
MM3  

Atomic & Metallic Radii

Atomic radius (Rahm)  
Metallic radius (C12)  

Numbering Scales

Mendeleev
Pettifor
Glawe

Electronegativity Scales

Ghosh
Miedema
Gunnarsson–Lundqvist
Robles–Bartolotti

Polarizability & Dispersion

Dipole polarizability  
Dipole polarizability (unc.)  
C₆ (Gould–Bučko)  

Miedema Parameters

Miedema molar volume  
Miedema electron density

Phase Transitions & Allotropes

Melting point301.65 K
Boiling point944.15 K
Critical point (temperature)1938.15 K
Critical point (pressure)9.4 MPa

Oxidation State Categories

−1 extended
+1 main

Advanced Reference Data

Screening Constants (12)
nOrbitalσ
1s1.0957
2p4.1804
2s14.4884
3d14.0194
3p18.4222
3s18.6226
4d32.1616
4p29.1424
4s27.9576
5p41.349
Crystal Radii Detail (6)
ChargeCNSpinrcrystal (pm)Origin
1VI181
1VIII188
1IX192
1X195
1XI199
1XII202
Isotope Decay Modes (74)
IsotopeModeIntensity
111p—
112p100%
112A0.3%
113p100%
114B+100%
114A0%
114B+p8.7%
114B+A0.2%
115B+100%
115B+p0.1%
X‑ray Scattering Factors (508)
Energy (eV)f₁f₂
10—0.04294
10.1617—0.04199
10.3261—0.04106
10.4931—0.04015
10.6628—0.03925
10.8353—0.03838
11.0106—0.04186
11.1886—0.04987
11.3696—0.06291
11.5535—0.06823

Additional Data

Sources

Sources of this element.

Cesium, an alkali metal, occurs in lepidolite, pollucte (a hydrated silicate of aluminum and cesium), and in other sources. One of the world's richest sources of cesium is located at Bernic Lake, Manitoba. The deposits are estimated to contain 300,000 tons of pollucite, averaging 20% cesium.

It can be isolated by elecytrolysis of the fused cyanide and by a number of other methods. Very pure, gas-free cesium can be prepared by thermal decomposition of cesium azide.

References (1)

References

(9)
2 Atomic Mass Data Center (AMDC), International Atomic Energy Agency (IAEA)
Cs

The half-life and atomic mass data was provided by the Atomic Mass Data Center at the International Atomic Energy Agency.

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3 IUPAC Commission on Isotopic Abundances and Atomic Weights (CIAAW)
Caesium

Element data are cited from the Atomic weights of the elements (an IUPAC Technical Report). The IUPAC periodic table of elements can be found at https://iupac.org/what-we-do/periodic-table-of-elements/. Additional information can be found within IUPAC publication doi:10.1515/pac-2015-0703 Copyright © 2020 International Union of Pure and Applied Chemistry.

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4 IUPAC Periodic Table of the Elements and Isotopes (IPTEI)

The information are cited from Pure Appl. Chem. 2018; 90(12): 1833-2092, https://doi.org/10.1515/pac-2015-0703.

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License note: Copyright (c) 2020 International Union of Pure and Applied Chemistry. The International Union of Pure and Applied Chemistry (IUPAC) contribution within Pubchem is provided under a CC-BY-NC-ND 4.0 license, unless otherwise stated.
5 Jefferson Lab, U.S. Department of Energy
Cesium

Thomas Jefferson National Accelerator Facility (Jefferson Lab) is one of 17 national laboratories funded by the U.S. Department of Energy. The lab's primary mission is to conduct basic research of the atom's nucleus using the lab's unique particle accelerator, known as the Continuous Electron Beam Accelerator Facility (CEBAF). For more information visit https://www.jlab.org/

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License note: Please see citation and linking information: https://education.jlab.org/faq/index.html
6 Los Alamos National Laboratory, U.S. Department of Energy
Cesium

The periodic table at the LANL (Los Alamos National Laboratory) contains basic element information together with the history, source, properties, use, handling and more. The provenance data may be found from the link under the source name.

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7 NIST Physical Measurement Laboratory
Cesium

The periodic table contains NIST's critically-evaluated data on atomic properties of the elements. The provenance data that include data for atomic spectroscopy, X-ray and gamma ray, radiation dosimetry, nuclear physics, and condensed matter physics may be found from the link under the source name. Ref: https://www.nist.gov/pml/atomic-spectra-database

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8 PubChem Elements
Cesium

This section provides all form of data related to element Cesium.

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9 PubChem Elements
Cesium

The element property data was retrieved from publications.

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Last updated:

Data verified:

Content is reviewed against latest scientific data.