81 Tl 204.38
Thallium
Post-Transition Metal
Thallium (Tl) is a chemical element with atomic number 81, classified as a post-transition metal. At room temperature it is a solid. It was discovered in 1861 by William Crookes.
Properties
- Atomic number
- 81
- Atomic mass
- 204.38 u
- Category
- Post-Transition Metal
- Group
- 13
- Period
- 6
- Block
- p-block
- Electron configuration
- [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p¹
- Phase at STP
- Solid
- Density
- 11.85 g/cm³
- Melting point
- 577 K (303.9 °C)
- Boiling point
- 1746 K (1472.8 °C)
- Electronegativity
- 1.62
- Atomic radius
- 156 pm
- Ionization energy
- 6.108 eV
- Discovery
- 1861 · William Crookes
Common uses
Electronics, glass, semiconductors, medical imaging
Did you know?
Extremely toxic and once used as rat poison and insecticide.
Experiment with the elements
Thallium doesn't form any compounds in our lab yet, but the periodic table sandbox lets you combine dozens of other real elements into real compounds — water, table salt, ammonia and many more — with their true chemical formulas.