Thallium

Thallium (Tl)

Pure, unreacted thallium appears silvery-white and exhibits a metallic lustre. Upon reacting with air, it begins to turn bluish-grey and looks like lead. It is very malleable, and can be cut with a knife. There are two stable isotopes, and four radioisotopes, Tl-204 being the most stable with a half-life of 3.78 years. Thallium sulphate was used as a rodenticide. Thallium sulphine's conductivity changes with exposure to infrared light, this gives it a use in infrared detectors. Discovered by Sir William Crookes via spectroscopy. Its name comes from the Greek word thallos, which means green twig. Thallium and its compounds are toxic and can cause cancer.
Atomic Number81
Atomic Weight204.38
Mass Number205
Group13
Period6
Blockp
Protons81 p+
Neutrons124 n0
Electrons81 e-
Thallium pieces in ampoule.jpg Thallium-croprotated.jpg Animated Bohr Model of Tl (Thallium) Enhanced Bohr Model of Tl (Thallium) Bohr Model: Tl (Thallium) Orbital Diagram of Tl (Thallium)

Properties

Atomic Radius
190 pm
Molar Volume
Covalent Radius
144 pm
Metallic Radius
144 pm
Ionic Radius
150 pm
Crystal Radius
164 pm
Van der Waals Radius
196 pm
Density
11.8 g/cm³
Energy
Proton Affinity
Electron Affinity
Ionization Energy
6.108287 eV/particle
Heat of Vaporization
162.4 kJ/mol
Heat of Fusion
4.31 kJ/mol
Heat of Formation
182.2 kJ/mol
Electrons
Electron Shells2, 8, 18, 32, 18, 3
Valence Electrons3
Electron Configuration[Xe] 4f14 5d10 6s2 6p1
Oxidation States-5, -2, -1, 1, 2, 3
Electronegativity
1.8
Electrophilicity
0.9173102715055317 eV/particle
Phases
PhaseSolid
Gas Phase
Boiling Point
1,746.15 K
Melting Point
577.15 K
Critical Pressure
Critical Temperature
Triple Point
Visual
Color
Silver
Appearancesilvery white
Refractive Index
Thermodynamic Properties
Thermal Conductivity
46.1 W/(m K)
Thermal Expansion
0.0000299 1/K
Molar Heat Capacity
26.32 J/(mol K)
Specific Heat Capacity
0.129 J/(g⋅K)
Heat Capacity Ratio (Adiabatic Index)
Electrical Properties
TypeConductor
Electrical Conductivity
6.7 MS/m
Electrical Resistivity
0.00000015 m Ω
Superconducting Point
2.38 K
Magnetism
Typediamagnetic
Magnetic Susceptibility (Mass)
-0.000000003 m³/Kg
Magnetic Susceptibility (Molar)
-0.000000000613 m³/mol
Magnetic Susceptibility (Volume)
-0.0000356
Magnetic Ordering
Curie Point
Neel Point
Structure
Crystal StructureSimple Hexagonal (HEX)
Lattice Constant
3.46 Å
Lattice Anglesπ/2, π/2, 2 π/3
Mechanical Properties
Hardness
1.2 MPa
Bulk Modulus
43 GPa
Shear Modulus
2.8 GPa
Young Modulus
8 GPa
Poisson Ratio
0.45
Speed of Sound
818 m/s
Classification
CategoryPost-transition metals, Poor metals
CAS GroupIIIB
IUPAC GroupIIIA
Glawe Number81
Mendeleev Number85
Pettifor Number78
Geochemical Class
Goldschmidt Classchalcophile
Other
Gas Basicity
Dipole Polarizability
50 ± 2 a₀
C6 Dispersion Coefficient
Allotropes
Neutron Cross Section
3.4
Neutron Mass Absorption
0.00059
Quantum Numbers2P1/2
Space Group194 (P63/mmc)

Isotopes of Thallium

Stable Isotopes2
Unstable Isotopes41
Radioactive Isotopes41

176Tl

AbundanceRadioactive ☢️
Relative Atomic Mass
176.000627731 ± 0.000089166 Da
Mass Number176
G-Factor
Half Life
6.2 ± 2.3 ms
Spin3
Quadrupole Moment
Discovery Year2004
Parity-

176Tl Decay Modes
Decay ModeIntensity
p (proton emission)100%
α (α emission)%
β+ (β+ decay; β+ = ϵ + e+)%

177Tl

AbundanceRadioactive ☢️
Relative Atomic Mass
176.996414252 ± 0.000023218 Da
Mass Number177
G-Factor
Half Life
18 ± 5 ms
Spin1/2
Quadrupole Moment
0
Discovery Year1999
Parity+

177Tl Decay Modes
Decay ModeIntensity
α (α emission)73%
p (proton emission)%

178Tl

AbundanceRadioactive ☢️
Relative Atomic Mass
177.995047 ± 0.00011 Da
Mass Number178
G-Factor
Half Life
255 ± 9 ms
Spin4
Quadrupole Moment
Discovery Year1997
Parity-

178Tl Decay Modes
Decay ModeIntensity
α (α emission)62%
β+ (β+ decay; β+ = ϵ + e+)38%
β+ SF (β+-delayed fission)0.15%

179Tl

AbundanceRadioactive ☢️
Relative Atomic Mass
178.991122185 ± 0.000041495 Da
Mass Number179
G-Factor
Half Life
437 ± 9 ms
Spin1/2
Quadrupole Moment
0
Discovery Year1983
Parity+

179Tl Decay Modes
Decay ModeIntensity
α (α emission)60%
β+ (β+ decay; β+ = ϵ + e+)%

180Tl

AbundanceRadioactive ☢️
Relative Atomic Mass
179.98991895 ± 0.000075058 Da
Mass Number180
G-Factor
Half Life
1.09 ± 0.01 s
Spin4
Quadrupole Moment
Discovery Year1987
Parity-

180Tl Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)93%
α (α emission)7%
β+ SF (β+-delayed fission)0.0032%

181Tl

AbundanceRadioactive ☢️
Relative Atomic Mass
180.986259978 ± 0.000009771 Da
Mass Number181
G-Factor
Half Life
2.9 ± 0.1 s
Spin1/2
Quadrupole Moment
0
Discovery Year1996
Parity+

181Tl Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)%
α (α emission)8.6%

182Tl

AbundanceRadioactive ☢️
Relative Atomic Mass
181.985692649 ± 0.000012856 Da
Mass Number182
G-Factor
Half Life
1.9 ± 0.1 s
Spin4
Quadrupole Moment
Discovery Year1991
Parity-

182Tl Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)100%
α (α emission)0.49%
β+ SF (β+-delayed fission)3.4%

183Tl

AbundanceRadioactive ☢️
Relative Atomic Mass
182.982192843 ± 0.000010017 Da
Mass Number183
G-Factor
Half Life
6.9 ± 0.7 s
Spin1/2
Quadrupole Moment
0
Discovery Year1980
Parity+

183Tl Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)%
α (α emission)%

184Tl

AbundanceRadioactive ☢️
Relative Atomic Mass
183.981874973 ± 0.000010747 Da
Mass Number184
G-Factor
Half Life
9.5 ± 0.2 s
Spin2
Quadrupole Moment
Discovery Year1976
Parity-

184Tl Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)98.78%
α (α emission)1.22%

185Tl

AbundanceRadioactive ☢️
Relative Atomic Mass
184.978789189 ± 0.000022194 Da
Mass Number185
G-Factor
Half Life
19.5 ± 0.5 s
Spin1/2
Quadrupole Moment
0
Discovery Year1976
Parity+

185Tl Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)100%
α (α emission)%

186Tl

AbundanceRadioactive ☢️
Relative Atomic Mass
185.978654787 ± 0.000022276 Da
Mass Number186
G-Factor
Half Life
3.5 ± 0.5 s
Spin2
Quadrupole Moment
Discovery Year1975
Parity-

186Tl Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)%
α (α emission)%

187Tl

AbundanceRadioactive ☢️
Relative Atomic Mass
186.97590474 ± 0.00000864 Da
Mass Number187
G-Factor
3.08 ± 0.12
Half Life
Spin1/2
Quadrupole Moment
0
Discovery Year1976
Parity+

187Tl Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)100%
α (α emission)%

188Tl

AbundanceRadioactive ☢️
Relative Atomic Mass
187.976020886 ± 0.000032103 Da
Mass Number188
G-Factor
Half Life
71 ± 2 s
Spin2
Quadrupole Moment
Discovery Year1970
Parity-

188Tl Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)100%

189Tl

AbundanceRadioactive ☢️
Relative Atomic Mass
188.973573525 ± 0.000008983 Da
Mass Number189
G-Factor
Half Life
2.3 ± 0.2 m
Spin1/2
Quadrupole Moment
0
Discovery Year1972
Parity+

189Tl Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)100%

190Tl

AbundanceRadioactive ☢️
Relative Atomic Mass
189.973841771 ± 0.000007784 Da
Mass Number190
G-Factor
Half Life
2.6 ± 0.3 m
Spin2
Quadrupole Moment
Discovery Year1970
Parity-

190Tl Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)100%

191Tl

AbundanceRadioactive ☢️
Relative Atomic Mass
190.971784093 ± 0.000007889 Da
Mass Number191
G-Factor
3.164 ± 0.008
Half Life
Spin1/2
Quadrupole Moment
0
Discovery Year1974
Parity+

191Tl Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)%

192Tl

AbundanceRadioactive ☢️
Relative Atomic Mass
191.972225 ± 0.000034 Da
Mass Number192
G-Factor
0.0995 ± 0.0015
Half Life
9.6 ± 0.4 m
Spin2
Quadrupole Moment
Discovery Year1961
Parity-

192Tl Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)100%

193Tl

AbundanceRadioactive ☢️
Relative Atomic Mass
192.970501994 ± 0.0000072 Da
Mass Number193
G-Factor
3.17 ± 0.006
Half Life
21.6 ± 0.8 m
Spin1/2
Quadrupole Moment
0
Discovery Year1960
Parity+

193Tl Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)100%

194Tl

AbundanceRadioactive ☢️
Relative Atomic Mass
193.971081408 ± 0.000015 Da
Mass Number194
G-Factor
0.0695 ± 0.0015
Half Life
33 ± 0.5 m
Spin2
Quadrupole Moment
-0.282 ± 0.007
Discovery Year1960
Parity-

194Tl Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)100%
α (α emission)%

195Tl

AbundanceRadioactive ☢️
Relative Atomic Mass
194.969774052 ± 0.000011944 Da
Mass Number195
G-Factor
3.14 ± 0.08
Half Life
1.16 ± 0.05 h
Spin1/2
Quadrupole Moment
0
Discovery Year1955
Parity+

195Tl Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)100%

196Tl

AbundanceRadioactive ☢️
Relative Atomic Mass
195.970481189 ± 0.000013 Da
Mass Number196
G-Factor
0.036 ± 0.0015
Half Life
1.84 ± 0.03 h
Spin2
Quadrupole Moment
-0.178 ± 0.014
Discovery Year1955
Parity-

196Tl Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)100%

197Tl

AbundanceRadioactive ☢️
Relative Atomic Mass
196.969560492 ± 0.000014573 Da
Mass Number197
G-Factor
3.14 ± 0.04
Half Life
2.84 ± 0.04 h
Spin1/2
Quadrupole Moment
0
Discovery Year1955
Parity+

197Tl Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)100%

198Tl

AbundanceRadioactive ☢️
Relative Atomic Mass
197.970446669 ± 0.0000081 Da
Mass Number198
G-Factor
0 ± 0.005
Half Life
5.3 ± 0.5 h
Spin2
Quadrupole Moment
Discovery Year1949
Parity-

198Tl Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)100%

199Tl

AbundanceRadioactive ☢️
Relative Atomic Mass
198.969877 ± 0.00003 Da
Mass Number199
G-Factor
3.18 ± 0.04
Half Life
7.42 ± 0.08 h
Spin1/2
Quadrupole Moment
0
Discovery Year1949
Parity+

199Tl Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)100%

200Tl

AbundanceRadioactive ☢️
Relative Atomic Mass
199.970963608 ± 0.000006182 Da
Mass Number200
G-Factor
0.02 ± 0.005
Half Life
26.1 ± 0.1 h
Spin2
Quadrupole Moment
Discovery Year1949
Parity-

200Tl Decay Modes
Decay ModeIntensity
β+ (β+ decay; β+ = ϵ + e+)100%

201Tl

AbundanceRadioactive ☢️
Relative Atomic Mass
200.970820235 ± 0.000015228 Da
Mass Number201
G-Factor
3.198 ± 0.006
Half Life
3.0421 ± 0.0008 d
Spin1/2
Quadrupole Moment
0
Discovery Year1950
Parity+

201Tl Decay Modes
Decay ModeIntensity
ϵ (electron capture)100%

202Tl

AbundanceRadioactive ☢️
Relative Atomic Mass
201.972108874 ± 0.000001972 Da
Mass Number202
G-Factor
0.03 ± 0.005
Half Life
12.31 ± 0.08 d
Spin2
Quadrupole Moment
Discovery Year1940
Parity-

202Tl Decay Modes
Decay ModeIntensity
ϵ (electron capture)100%

203Tl

Abundance
29.515 ± 0.044
Relative Atomic Mass
202.972344098 ± 0.000001257 Da
Mass Number203
G-Factor
Half Life
Spin1/2
Quadrupole Moment
0
Discovery Year1931
Parity+

204Tl

AbundanceRadioactive ☢️
Relative Atomic Mass
203.97386342 ± 0.000001238 Da
Mass Number204
G-Factor
0.045 ± 0.005
Half Life
3.783 ± 0.012 y
Spin2
Quadrupole Moment
Discovery Year1953
Parity-

204Tl Decay Modes
Decay ModeIntensity
β (β decay)97.08%
EC+B+2.92%

205Tl

Abundance
70.485 ± 0.044
Relative Atomic Mass
204.974427318 ± 0.00000133 Da
Mass Number205
G-Factor
Half Life
Spin1/2
Quadrupole Moment
0
Discovery Year1931
Parity+

206Tl

AbundanceRadioactive ☢️
Relative Atomic Mass
205.976110108 ± 0.00000138 Da
Mass Number206
G-Factor
0
Half Life
4.202 ± 0.011 m
Spin0
Quadrupole Moment
0
Discovery Year1935
Parity-

206Tl Decay Modes
Decay ModeIntensity
β (β decay)100%

207Tl

AbundanceRadioactive ☢️
Relative Atomic Mass
206.977418605 ± 0.000005839 Da
Mass Number207
G-Factor
3.738 ± 0.01
Half Life
4.77 ± 0.02 m
Spin1/2
Quadrupole Moment
0
Discovery Year1908
Parity+

207Tl Decay Modes
Decay ModeIntensity
β (β decay)100%

208Tl

AbundanceRadioactive ☢️
Relative Atomic Mass
207.982018006 ± 0.000001989 Da
Mass Number208
G-Factor
0.0582 ± 0.0026
Half Life
3.053 ± 0.004 m
Spin5
Quadrupole Moment
Discovery Year1909
Parity+

208Tl Decay Modes
Decay ModeIntensity
β (β decay)100%

209Tl

AbundanceRadioactive ☢️
Relative Atomic Mass
208.985351713 ± 0.000006559 Da
Mass Number209
G-Factor
Half Life
2.162 ± 0.007 m
Spin1/2
Quadrupole Moment
0
Discovery Year1950
Parity+

209Tl Decay Modes
Decay ModeIntensity
β (β decay)100%
β n (β-delayed neutron emission)%

210Tl

AbundanceRadioactive ☢️
Relative Atomic Mass
209.990072942 ± 0.000012456 Da
Mass Number210
G-Factor
Half Life
1.3 ± 0.03 m
Spin5
Quadrupole Moment
Discovery Year1909
Parity+

210Tl Decay Modes
Decay ModeIntensity
β (β decay)100%
β n (β-delayed neutron emission)0.009%

211Tl

AbundanceRadioactive ☢️
Relative Atomic Mass
210.993475 ± 0.000045 Da
Mass Number211
G-Factor
Half Life
81 ± 16 s
Spin1/2
Quadrupole Moment
0
Discovery Year1998
Parity+

211Tl Decay Modes
Decay ModeIntensity
β (β decay)100%
β n (β-delayed neutron emission)2.2%

212Tl

AbundanceRadioactive ☢️
Relative Atomic Mass
211.998335 ± 0.000215 Da
Mass Number212
G-Factor
Half Life
31 ± 8 s
Spin5
Quadrupole Moment
Discovery Year1998
Parity+

212Tl Decay Modes
Decay ModeIntensity
β (β decay)100%
β n (β-delayed neutron emission)1.8%

213Tl

AbundanceRadioactive ☢️
Relative Atomic Mass
213.001915 ± 0.000029 Da
Mass Number213
G-Factor
Half Life
23.8 ± 4.4 s
Spin1/2
Quadrupole Moment
0
Discovery Year2010
Parity+

213Tl Decay Modes
Decay ModeIntensity
β (β decay)100%
β n (β-delayed neutron emission)7.6%

214Tl

AbundanceRadioactive ☢️
Relative Atomic Mass
214.00694 ± 0.00021 Da
Mass Number214
G-Factor
Half Life
11 ± 2.4 s
Spin5
Quadrupole Moment
Discovery Year2010
Parity+

214Tl Decay Modes
Decay ModeIntensity
β (β decay)100%
β n (β-delayed neutron emission)34%

215Tl

AbundanceRadioactive ☢️
Relative Atomic Mass
215.010768 ± 0.000322 Da
Mass Number215
G-Factor
Half Life
9.7 ± 3.8 s
Spin1/2
Quadrupole Moment
0
Discovery Year2010
Parity+

215Tl Decay Modes
Decay ModeIntensity
β (β decay)100%
β n (β-delayed neutron emission)4.6%

216Tl

AbundanceRadioactive ☢️
Relative Atomic Mass
216.015964 ± 0.000322 Da
Mass Number216
G-Factor
Half Life
5.9 ± 3.3 s
Spin5
Quadrupole Moment
Discovery Year2010
Parity+

216Tl Decay Modes
Decay ModeIntensity
β (β decay)100%
β n (β-delayed neutron emission)11.5%

217Tl

AbundanceRadioactive ☢️
Relative Atomic Mass
217.020032 ± 0.000429 Da
Mass Number217
G-Factor
Half Life
Spin1/2
Quadrupole Moment
0
Discovery Year2010
Parity+

217Tl Decay Modes
Decay ModeIntensity
β (β decay)%
β n (β-delayed neutron emission)%

218Tl

AbundanceRadioactive ☢️
Relative Atomic Mass
218.025454 ± 0.000429 Da
Mass Number218
G-Factor
Half Life
Spin6
Quadrupole Moment
Discovery Year
Parity+

218Tl Decay Modes
Decay ModeIntensity
β (β decay)%
β n (β-delayed neutron emission)%

History

Thallium was discovered spectroscopically by Sir William Crookes in 1861, in London. In 1862, Claude-Auguste Lamy used a spectrometer to determine the composition of a selenium-containing substance which was deposited during the production of sulfuric acid from pyrite. He noticed the new green line in the spectra and concluded that a new element was present. From Greek thallos, meanin a green shoot or twig

DiscoverersSir William Crookes
Discovery LocationEngland
Discovery Year1861
Etymology (Name Origin)Greek: thallos (green twig), for a bright green line in its spectrum.
PronunciationTHAL-i-em (English)
Thallium and its compounds are highly toxic
Agatha Christie made use of thallium's toxicity in her novel The Pale Horse

Uses

Thallium selenide has been used in a bolometer for infrared detection. Thallium is also used in gamma radiation detection equipment. Thallium oxide has been used to produce glasses with a high index of refraction, and is used in the manufacture of photo cells. Some of the electrodes in dissolved oxygen analyzers contain thallium. Its compounds are used in rat and ant poisons. Also for detecting infrared radiation.

Sources

Found in iron pyrites. Also in crookesite, hutchinsonite and lorandite. Most is recovered from the byproducts of lead and zinc refining.

Abundance
Abundance in Earth's crust
0.85 mg/kg
Abundance in Oceans
0.000019 mg/L
Abundance in Human Body
Abundance in Meteor
0.0000078 %
Abundance in Sun
0.0000001 %
Abundance in Universe
0.00000005 %

Nuclear Screening Constants

1s1.5591
2p4.5138
2s21.3158
3d13.4658
3p22.6335
3s23.5809
4d37.6112
4f38.1324
4p35.7832
4s34.9212
5d58.975
5p53.9115
5s51.878
6p68.7462
6s68.1804