Thallium
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.
Gallery
Hi-Res Images ofChemical Elements, CC BY 3.0 <https://creativecommons.org/licenses/by/3.0>, via Wikimedia Commons, source: https://images-of-elements.com/thallium.php
Physical Propertiesmass · density · phase · crystal
Atomic Mass
204.3800Da
Density
11.8000g/cm³
Phase (STP)
Solid
Melting Point
577.1K
Boiling Point
1746.2K
Molar Heat
0.1290J/(mol·K)
Crystal Structure
HEX
Lattice Constant
3.460Å
Atomic Radiiatomic · covalent · van der Waals
Atomic (Empirical)
190.00pm
Covalent
144.00pm
Van der Waals
196.00pm
Electronic Propertieselectronegativity · ionization · affinity
Electron Configuration
[Xe] 4f14 5d10 6s2 6p
Electron Shells
2, 8, 18, 32, 18, 3
Electronegativity
1.80Pauling
Electron Affinity
0.4kJ/mol
1st Ionization Energy
6.1kJ/mol
Oxidation States
+1, +3
Orbital DiagramAufbau · Hund's rule · Pauli exclusion
Full: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p6 4f14 5d10 6s2 6p1Short: [Xe] 4f14 5d10 6s2 6p
Ionization Energies (81 known)
Emission Spectrumvisible range · characteristic spectral lines
Abundanceby mass
Log scale · ppm = parts per million by mass
Biological Role
Extremely toxic — 'poisoner\'s poison.' Causes alopecia. Tl-201 used in cardiac imaging.
Discovery
Discovered By
Sir William Crookes
Named By
—
Year
1861
Nuclear Data
Known Isotopes
43
Stable Isotopes
2
Stable Mass Numbers
203, 205
Natural isotopic abundance (IUPAC recommended values)
Isotopes of Tl43 known
| Nuclide | Z | N | Mass (AMU) | Half-life | Decay | Jπ | Abundance |
|---|---|---|---|---|---|---|---|
| 176Tl | 81 | 95 | 176.000628 | 6.20 ms | p (1%), α, β⁺ | 3- | — |
| 177Tl | 81 | 96 | 176.996414 | 18.0 ms | α (0.73%), p | 1/2+ | — |
| 178Tl | 81 | 97 | 177.995047 | 255 ms | α (0.62%), β⁺ (0.38%), β⁺SF (0.0015%) | 4- | — |
| 203Tlstable | 81 | 122 | 202.972344 | Stable | stable (1%) | 1/2+ | 2951.5000% |
| 205Tlstable | 81 | 124 | 204.974427 | Stable | stable (1%) | 1/2+ | 7048.5000% |
| 216Tl | 81 | 135 | 216.015964 | 5.90 s | β⁻ (1%), β⁻n (0.115%) | 5+ | — |
| 217Tl | 81 | 136 | 217.020032 | Unknown | β⁻, β⁻n | 1/2+ | — |
| 218Tl | 81 | 137 | 218.025454 | Unknown | β⁻, β⁻n | 6+ | — |