Thallium (Tl)
Thallium (Tl) is element 81, a post-transition metal. Atomic mass 204.38, configuration [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p¹. Properties, isotopes, oxidation states, uses and history, with an interactive 3D atom model.
Key facts
| Atomic number | 81 |
|---|---|
| Symbol | Tl |
| Standard atomic weight | [204.382,204.385] |
| Category | Post-transition Metal |
| Group | 13 |
| Period | 6 |
| State at room temperature | Solid |
| Electron configuration | [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p¹ |
| Valence electrons | 3 |
| Common oxidation states | +1, +3 |
| Common ions | No common ions |
| Electronegativity (Pauling) | 1.8 |
| First ionization energy | 589 kJ/mol |
| Electron affinity | 36.38 kJ/mol |
| Atomic radius | 190 pm |
| Density | 11.8 g/cm³ |
| Melting point | 304°C |
| Boiling point | 1473°C |
| Specific heat | 0.129 J/(g·°C) |
Natural isotopes
- Tl-203: Stable
- Tl-205: Stable
Common uses
- Rat poison (banned)
- Electronics
- Cardiac stress tests (Tl-201)
Where it matters
- Forensic Science ("The Poisoner's Poison")
Hazards
- Extremely toxic
- accumulates in body
History
| Discovered | 1861 |
|---|---|
| Discovered by | William Crookes |
| Name | From Greek thallos (green twig) |