Cesium

Cesium (Cs)

Soft silvery-white metallic element belonging to group 1 of the periodic table. One of the three metals which are liquid at room temperature. Cs-133 is the natural, and only stable, isotope. Fifteen other radioisotopes exist. Caesium reacts explosively with cold water, and ice at temperatures above 157K. Caesium hydroxide is the strongest base known. Caesium is the most electropositive, most alkaline and has the least ionization potential of all the elements. Known uses include the basis of atomic clocks, catalyst for the hydrogenation of some organic compounds, and in photoelectric cells. Caesium was discovered by Gustav Kirchoff and Robert Bunsen in Germany in 1860 spectroscopically. Its identification was based upon the bright blue lines in its spectrum. The name comes from the latin word caesius, which means sky blue. Caesium should be considered highly toxic. Some of the radioisotopes are even more toxic.
Atomic Number55
Atomic Weight132.90545196
Mass Number133
Group1
Period6
Blocks
Protons55 p+
Neutrons78 n0
Electrons55 e-
Cesium.jpg Animated Bohr Model of Cs (Cesium) Enhanced Bohr Model of Cs (Cesium) Bohr Model: Cs (Cesium) Orbital Diagram of Cs (Cesium)

Properties

Atomic Radius
260 pm
Molar Volume
Covalent Radius
232 pm
Metallic Radius
235 pm
Ionic Radius
167 pm
Crystal Radius
181 pm
Van der Waals Radius
343 pm
Density
1.873 g/cm³
Energy
Proton Affinity
Electron Affinity
0.471626 eV/particle
Ionization Energy
3.893905548 eV/particle
Heat of Vaporization
68.3 kJ/mol
Heat of Fusion
2.09 kJ/mol
Heat of Formation
76.5 kJ/mol
Electrons
Electron Shells2, 8, 18, 18, 8, 1
Valence Electrons1
Electron Configuration[Xe] 6s1
Oxidation States-1, 1
Electronegativity
0.79
Electrophilicity
0.696095447101947 eV/particle
Phases
PhaseSolid
Gas Phase
Boiling Point
944.15 K
Melting Point
301.65 K
Critical Pressure
9.4 MPa
Critical Temperature
1,938.15 K
Triple Point
Visual
Color
Silver
Appearancesilvery gold
Refractive Index
Thermodynamic Properties
Thermal Conductivity
35.9 W/(m K)
Thermal Expansion
Molar Heat Capacity
32.21 J/(mol K)
Specific Heat Capacity
0.242 J/(g⋅K)
Heat Capacity Ratio (Adiabatic Index)
Electrical Properties
TypeConductor
Electrical Conductivity
5 MS/m
Electrical Resistivity
0.0000002 m Ω
Superconducting Point
Magnetism
Typeparamagnetic
Magnetic Susceptibility (Mass)
0.0000000028 m³/Kg
Magnetic Susceptibility (Molar)
0.000000000372 m³/mol
Magnetic Susceptibility (Volume)
0.00000526
Magnetic Ordering
Curie Point
Neel Point
Structure
Crystal StructureBody Centered Cubic (BCC)
Lattice Constant
6.05 Å
Lattice Anglesπ/2, π/2, π/2
Mechanical Properties
Hardness
0.2 MPa
Bulk Modulus
1.6 GPa
Shear Modulus
Young Modulus
1.7 GPa
Poisson Ratio
Speed of Sound
Classification
CategoryAlkali metals, Alkali metals
CAS GroupIA
IUPAC GroupIA
Glawe Number8
Mendeleev Number5
Pettifor Number8
Geochemical Classalkali metal
Goldschmidt Classlitophile
Other
Gas Basicity
Dipole Polarizability
400.9 ± 0.7 a₀
C6 Dispersion Coefficient
Allotropes
Neutron Cross Section
29
Neutron Mass Absorption
0.0077
Quantum Numbers2S1/2
Space Group229 (Im_3m)

Isotopes of Cesium

Stable Isotopes1
Unstable Isotopes41
Radioactive Isotopes41

111Cs

AbundanceRadioactive ☢️
Relative Atomic Mass
110.953945 ± 0.000215 Da
Mass Number111
G-Factor
Half Life
Spin3/2
Quadrupole Moment
Discovery Year
Parity+

111Cs Decay Modes
Decay ModeIntensity
p (proton emission)%

112Cs

AbundanceRadioactive ☢️
Relative Atomic Mass
111.950172 ± 0.000124 Da
Mass Number112
G-Factor
Half Life
490 ± 30 us
Spin1
Quadrupole Moment
Discovery Year1994
Parity+

112Cs Decay Modes
Decay ModeIntensity
p (proton emission)100%
α (α emission)0.26%

113Cs

AbundanceRadioactive ☢️
Relative Atomic Mass
112.944428484 ± 0.000009207 Da
Mass Number113
G-Factor
Half Life
16.94 ± 0.09 us
Spin3/2
Quadrupole Moment
Discovery Year1984
Parity+

113Cs Decay Modes
Decay ModeIntensity
p (proton emission)100%

114Cs

AbundanceRadioactive ☢️
Relative Atomic Mass
113.941292244 ± 0.000091323 Da
Mass Number114
G-Factor
Half Life
570 ± 20 ms
Spin1
Quadrupole Moment
Discovery Year1978
Parity+

114Cs Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)100%
α (α emission)0.018%
β+ p (β+-delayed proton emission)8.7%
β+α (β+-delayed α emission)0.19%

115Cs

AbundanceRadioactive ☢️
Relative Atomic Mass
114.93591 ± 0.00011 Da
Mass Number115
G-Factor
Half Life
1.4 ± 0.8 s
Spin9/2
Quadrupole Moment
Discovery Year1978
Parity+

115Cs Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)100%
β+ p (β+-delayed proton emission)0.07%

116Cs

AbundanceRadioactive ☢️
Relative Atomic Mass
115.933395 ± 0.000108 Da
Mass Number116
G-Factor
Half Life
700 ± 40 ms
Spin1
Quadrupole Moment
Discovery Year1975
Parity+

116Cs Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)100%
β+ p (β+-delayed proton emission)0.28%
β+α (β+-delayed α emission)0.049%

117Cs

AbundanceRadioactive ☢️
Relative Atomic Mass
116.928616723 ± 0.000067 Da
Mass Number117
G-Factor
Half Life
8.4 ± 0.6 s
Spin9/2
Quadrupole Moment
Discovery Year1972
Parity+

117Cs Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)100%

118Cs

AbundanceRadioactive ☢️
Relative Atomic Mass
117.926559517 ± 0.00001369 Da
Mass Number118
G-Factor
1.935 ± 0.0025
Half Life
14 ± 2 s
Spin2
Quadrupole Moment
1.31 ± 0.17
Discovery Year1969
Parity+

118Cs Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)100%
β+ p (β+-delayed proton emission)0.021%
β+α (β+-delayed α emission)0.0012%

119Cs

AbundanceRadioactive ☢️
Relative Atomic Mass
118.922377327 ± 0.000014965 Da
Mass Number119
G-Factor
1.2111111111111 ± 0.0066666666666667
Half Life
43 ± 0.2 s
Spin9/2
Quadrupole Moment
2.65 ± 0.17
Discovery Year1969
Parity+

119Cs Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)100%
β+α (β+-delayed α emission)2%

120Cs

AbundanceRadioactive ☢️
Relative Atomic Mass
119.920677277 ± 0.000010702 Da
Mass Number120
G-Factor
1.93 ± 0.01
Half Life
60.4 ± 0.6 s
Spin2
Quadrupole Moment
1.36 ± 0.07
Discovery Year1969
Parity+

120Cs Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)100%
β+α (β+-delayed α emission)2%
β+ p (β+-delayed proton emission)7%

121Cs

AbundanceRadioactive ☢️
Relative Atomic Mass
120.917227235 ± 0.00001534 Da
Mass Number121
G-Factor
0.51266666666667 ± 0.0026666666666667
Half Life
155 ± 4 s
Spin3/2
Quadrupole Moment
0.79 ± 0.04
Discovery Year1969
Parity+

121Cs Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)100%

122Cs

AbundanceRadioactive ☢️
Relative Atomic Mass
121.916108144 ± 0.000036164 Da
Mass Number122
G-Factor
0.133 ± 0.002
Half Life
21.18 ± 0.19 s
Spin1
Quadrupole Moment
-0.179 ± 0.01
Discovery Year1969
Parity+

122Cs Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)100%
β+α (β+-delayed α emission)2%

123Cs

AbundanceRadioactive ☢️
Relative Atomic Mass
122.91299606 ± 0.000013 Da
Mass Number123
G-Factor
2.75 ± 0.014
Half Life
5.88 ± 0.03 m
Spin1/2
Quadrupole Moment
0
Discovery Year1954
Parity+

123Cs Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)100%

124Cs

AbundanceRadioactive ☢️
Relative Atomic Mass
123.912247366 ± 0.000009823 Da
Mass Number124
G-Factor
0.672 ± 0.003
Half Life
30.9 ± 0.4 s
Spin1
Quadrupole Moment
-0.69 ± 0.04
Discovery Year1969
Parity+

124Cs Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)100%

125Cs

AbundanceRadioactive ☢️
Relative Atomic Mass
124.909725953 ± 0.000008304 Da
Mass Number125
G-Factor
2.814 ± 0.014
Half Life
44.35 ± 0.29 m
Spin1/2
Quadrupole Moment
0
Discovery Year1954
Parity+

125Cs Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)100%

126Cs

AbundanceRadioactive ☢️
Relative Atomic Mass
125.909445821 ± 0.00001112 Da
Mass Number126
G-Factor
0.776 ± 0.004
Half Life
1.64 ± 0.02 m
Spin1
Quadrupole Moment
-0.64 ± 0.03
Discovery Year1954
Parity+

126Cs Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)100%

127Cs

AbundanceRadioactive ☢️
Relative Atomic Mass
126.907417527 ± 0.000005987 Da
Mass Number127
G-Factor
2.914 ± 0.014
Half Life
6.25 ± 0.1 h
Spin1/2
Quadrupole Moment
0
Discovery Year1950
Parity+

127Cs Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)100%

128Cs

AbundanceRadioactive ☢️
Relative Atomic Mass
127.907748452 ± 0.000005771 Da
Mass Number128
G-Factor
0.972 ± 0.005
Half Life
3.64 ± 0.014 m
Spin1
Quadrupole Moment
-0.54 ± 0.03
Discovery Year1951
Parity+

128Cs Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)100%

129Cs

AbundanceRadioactive ☢️
Relative Atomic Mass
128.90606591 ± 0.000004888 Da
Mass Number129
G-Factor
2.978 ± 0.016
Half Life
32.06 ± 0.06 h
Spin1/2
Quadrupole Moment
0
Discovery Year1950
Parity+

129Cs Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)100%

130Cs

AbundanceRadioactive ☢️
Relative Atomic Mass
129.906709281 ± 0.000008971 Da
Mass Number130
G-Factor
1.458 ± 0.007
Half Life
29.21 ± 0.04 m
Spin1
Quadrupole Moment
-0.056 ± 0.006
Discovery Year1952
Parity+

130Cs Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)98.4%
β (β decay)1.6%

131Cs

AbundanceRadioactive ☢️
Relative Atomic Mass
130.905468457 ± 0.00000019 Da
Mass Number131
G-Factor
1.4144 ± 0.0012
Half Life
9.689 ± 0.016 d
Spin5/2
Quadrupole Moment
0.59 ± 0.02
Discovery Year1947
Parity+

131Cs Decay Modes
Decay ModeIntensity
ϵ (electron capture)100%

132Cs

AbundanceRadioactive ☢️
Relative Atomic Mass
131.90643774 ± 0.000001112 Da
Mass Number132
G-Factor
1.1095 ± 0.0035
Half Life
6.48 ± 0.006 d
Spin2
Quadrupole Moment
0.48 ± 0.02
Discovery Year1953
Parity+

132Cs Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)98.13%
β (β decay)1.87%

133Cs

Abundance
100
Relative Atomic Mass
132.905451958 ± 0.000000008 Da
Mass Number133
G-Factor
0.73651428571429 ± 0.0004
Half Life
Spin7/2
Quadrupole Moment
-0.00343 ± 0.0001
Discovery Year1921
Parity+

134Cs

AbundanceRadioactive ☢️
Relative Atomic Mass
133.906718501 ± 0.000000017 Da
Mass Number134
G-Factor
0.747325 ± 0.00035
Half Life
2.065 ± 0.0004 y
Spin4
Quadrupole Moment
0.37 ± 0.02
Discovery Year1940
Parity+

134Cs Decay Modes
Decay ModeIntensity
β (β decay)100%
ϵ (electron capture)0.0003%

135Cs

AbundanceRadioactive ☢️
Relative Atomic Mass
134.905976907 ± 0.00000039 Da
Mass Number135
G-Factor
0.77951428571429 ± 0.00037142857142857
Half Life
1.33 ± 0.19 My
Spin7/2
Quadrupole Moment
0.048 ± 0.003
Discovery Year1949
Parity+

135Cs Decay Modes
Decay ModeIntensity
β (β decay)100%

136Cs

AbundanceRadioactive ☢️
Relative Atomic Mass
135.907311431 ± 0.00000201 Da
Mass Number136
G-Factor
0.741 ± 0.003
Half Life
13.01 ± 0.05 d
Spin5
Quadrupole Moment
0.213 ± 0.015
Discovery Year1951
Parity+

136Cs Decay Modes
Decay ModeIntensity
β (β decay)100%

137Cs

AbundanceRadioactive ☢️
Relative Atomic Mass
136.907089296 ± 0.000000324 Da
Mass Number137
G-Factor
0.81068571428571 ± 0.0004
Half Life
30.04 ± 0.04 y
Spin7/2
Quadrupole Moment
0.048 ± 0.002
Discovery Year1951
Parity+

137Cs Decay Modes
Decay ModeIntensity
β (β decay)100%

138Cs

AbundanceRadioactive ☢️
Relative Atomic Mass
137.911017119 ± 0.000009831 Da
Mass Number138
G-Factor
0.233 ± 0.0013333333333333
Half Life
33.5 ± 0.2 m
Spin3
Quadrupole Moment
0.112 ± 0.017
Discovery Year1943
Parity-

138Cs Decay Modes
Decay ModeIntensity
β (β decay)100%

139Cs

AbundanceRadioactive ☢️
Relative Atomic Mass
138.913363822 ± 0.000003364 Da
Mass Number139
G-Factor
0.768 ± 0.0011428571428571
Half Life
9.27 ± 0.05 m
Spin7/2
Quadrupole Moment
-0.063 ± 0.014
Discovery Year1939
Parity+

139Cs Decay Modes
Decay ModeIntensity
β (β decay)100%

140Cs

AbundanceRadioactive ☢️
Relative Atomic Mass
139.917283707 ± 0.000008801 Da
Mass Number140
G-Factor
0.134 ± 0.001
Half Life
63.7 ± 0.3 s
Spin1
Quadrupole Moment
-0.094 ± 0.015
Discovery Year1950
Parity-

140Cs Decay Modes
Decay ModeIntensity
β (β decay)100%

141Cs

AbundanceRadioactive ☢️
Relative Atomic Mass
140.920045279 ± 0.000009871 Da
Mass Number141
G-Factor
0.69457142857143 ± 0.0028571428571429
Half Life
24.84 ± 0.16 s
Spin7/2
Quadrupole Moment
-0.42 ± 0.07
Discovery Year1962
Parity+

141Cs Decay Modes
Decay ModeIntensity
β (β decay)100%
β n (β-delayed neutron emission)0.0342%

142Cs

AbundanceRadioactive ☢️
Relative Atomic Mass
141.924299514 ± 0.000007586 Da
Mass Number142
G-Factor
0
Half Life
1.687 ± 0.01 s
Spin0
Quadrupole Moment
0
Discovery Year1962
Parity-

142Cs Decay Modes
Decay ModeIntensity
β (β decay)100%
β n (β-delayed neutron emission)0.089%

143Cs

AbundanceRadioactive ☢️
Relative Atomic Mass
142.927347346 ± 0.00000813 Da
Mass Number143
G-Factor
0.57933333333333 ± 0.0026666666666667
Half Life
1.802 ± 0.008 s
Spin3/2
Quadrupole Moment
0.44 ± 0.03
Discovery Year1962
Parity+

143Cs Decay Modes
Decay ModeIntensity
β (β decay)100%
β n (β-delayed neutron emission)1.62%

144Cs

AbundanceRadioactive ☢️
Relative Atomic Mass
143.932075402 ± 0.000021612 Da
Mass Number144
G-Factor
-0.545 ± 0.003
Half Life
994 ± 6 ms
Spin1
Quadrupole Moment
0.29 ± 0.02
Discovery Year1967
Parity-

144Cs Decay Modes
Decay ModeIntensity
β (β decay)100%
β n (β-delayed neutron emission)2.98%

145Cs

AbundanceRadioactive ☢️
Relative Atomic Mass
144.935528927 ± 0.000009733 Da
Mass Number145
G-Factor
0.522 ± 0.0026666666666667
Half Life
582 ± 4 ms
Spin3/2
Quadrupole Moment
0.58 ± 0.06
Discovery Year1971
Parity+

145Cs Decay Modes
Decay ModeIntensity
β (β decay)100%
β n (β-delayed neutron emission)12.8%

146Cs

AbundanceRadioactive ☢️
Relative Atomic Mass
145.940621867 ± 0.000003106 Da
Mass Number146
G-Factor
-0.514 ± 0.002
Half Life
321.6 ± 0.9 ms
Spin1
Quadrupole Moment
0.21 ± 0.03
Discovery Year1971
Parity-

146Cs Decay Modes
Decay ModeIntensity
β (β decay)100%
β n (β-delayed neutron emission)14.2%
2n (2-neutron emission)%

147Cs

AbundanceRadioactive ☢️
Relative Atomic Mass
146.944261512 ± 0.000009 Da
Mass Number147
G-Factor
Half Life
230.5 ± 0.9 ms
Spin3/2
Quadrupole Moment
Discovery Year1978
Parity+

147Cs Decay Modes
Decay ModeIntensity
β (β decay)100%
β n (β-delayed neutron emission)28.5%

148Cs

AbundanceRadioactive ☢️
Relative Atomic Mass
147.949639026 ± 0.000014 Da
Mass Number148
G-Factor
Half Life
151.8 ± 1 ms
Spin2
Quadrupole Moment
Discovery Year1978
Parity-

148Cs Decay Modes
Decay ModeIntensity
β (β decay)100%
β n (β-delayed neutron emission)28.7%
2n (2-neutron emission)%

149Cs

AbundanceRadioactive ☢️
Relative Atomic Mass
148.953516 ± 0.000429 Da
Mass Number149
G-Factor
Half Life
112.3 ± 2.5 ms
Spin3/2
Quadrupole Moment
Discovery Year1979
Parity+

149Cs Decay Modes
Decay ModeIntensity
β (β decay)100%
β n (β-delayed neutron emission)25%
2n (2-neutron emission)%

150Cs

AbundanceRadioactive ☢️
Relative Atomic Mass
149.959023 ± 0.000429 Da
Mass Number150
G-Factor
Half Life
81 ± 2.6 ms
Spin2
Quadrupole Moment
Discovery Year1979
Parity-

150Cs Decay Modes
Decay ModeIntensity
β (β decay)100%
β n (β-delayed neutron emission)44%
2n (2-neutron emission)%

151Cs

AbundanceRadioactive ☢️
Relative Atomic Mass
150.963199 ± 0.000537 Da
Mass Number151
G-Factor
Half Life
59 ± 19 ms
Spin3/2
Quadrupole Moment
Discovery Year1979
Parity+

151Cs Decay Modes
Decay ModeIntensity
β (β decay)100%
β n (β-delayed neutron emission)%
2n (2-neutron emission)%

152Cs

AbundanceRadioactive ☢️
Relative Atomic Mass
151.968728 ± 0.000537 Da
Mass Number152
G-Factor
Half Life
Spin
Quadrupole Moment
Discovery Year1987
Parity

152Cs Decay Modes
Decay ModeIntensity
β (β decay)%
β n (β-delayed neutron emission)%

History

Robert Bunsen and Gustav Kirchhoff were the first to suggest finding cesium in 1860 by spectrum analysis. They discovered cesium by its two blue emission lines in a sample of Dürkheim mineral water. The pure metal was eventually isolated by the German chemist Carl Setterberg while working on his doctorate with Kekulé and Bunsen. From the Latin word caesius, sky blue

DiscoverersGustov Kirchoff, Robert Bunsen
Discovery LocationGermany
Discovery Year1860
Etymology (Name Origin)Latin: coesius (sky blue); for the blue lines of its spectrum.
PronunciationSEE-zi-em (English)
Cesium compounds are considered to be mildly toxic
Cesium was the first element discovered using a spectroscope

Uses

The radioactive isotope cesium-137 has a half-life of about 30 years and is used in medical applications, industrial gauges, and hydrology. Cesium is also used in photoelectric cells and as a catalyst in the hydrogenation of organic compounds. Cesium vapor thermionic generators are low-power devices that convert heat energy to electrical energy. Used as a 'getter' to remove air traces in vacuum and cathode-ray tubes. Also used in producing photoelectric devices and atomic clocks. Since it ionizes readily, it is used as an ion rocket motor propellant.

Sources

Found in pollucite [(Cs4Al4Si9O26).H2O] and as trace in lepidolite.

Abundance
Abundance in Earth's crust
Abundance in Oceans
0.0003 mg/L
Abundance in Human Body
0.000002 %
Abundance in Meteor
0.000014 %
Abundance in Sun
0.0000008 %
Abundance in Universe
0.00000008 %

Nuclear Screening Constants

1s1.0957
2p4.1804
2s14.4884
3d14.0194
3p18.4222
3s18.6226
4d32.1616
4p29.1424
4s27.9576
5p41.349
5s39.5555
6s48.637