Element 81
Thallium (Tl)
Thallium (Tl) is element 81 of the periodic table, a post-transition metal in period 6, group 13 (p-block) with an atomic mass of 204.38 and is a solid at standard conditions.
At a glance
- Atomic number
- 81
- Symbol
- Tl
- Atomic mass
- 204.38 u
- Category
- Post-transition metals
- Period
- 6
- Group
- 13
- Block
- p-block
- Phase at STP
- solid
Electron structure
- Electron configuration
- 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s2 6p1
- Shorthand configuration
- [Xe] 4f14 5d10 6s2 6p1
- Electrons per shell
- 2, 8, 18, 32, 18, 3
- Oxidation states
- -5, -2, -1, +1, +3
Physical properties
- Melting point
- 577 K
- Boiling point
- 1746 K
- Density
- 11.85 g/cm3
- Phase
- solid
Atomic properties
- Electronegativity (Pauling)
- 1.62
- Atomic radius
- 156 pm
- Covalent radius
- 145 pm
- Van der Waals radius
- 196 pm
- First ionization energy
- 589 kJ/mol
- Electron affinity
- 19 kJ/mol
Notable isotopes
| Isotope | Mass | Abundance | Stability |
|---|---|---|---|
| Tl-205 | 204.97441 | 70.48% | Stable |
Common uses
- Electronics
- Medical imaging
- Low-temperature thermometers
- Infrared detectors
Discovery
- Year
- 1861
- Discovered by
- William Crookes
- Country
- England