Tl
Thallium
Atomic number: 81Mass: 204.38 uCategory: Post-Transition Metal
About Thallium
Thallium is a soft grey post-transition metal. It is highly toxic and was once used as a rat poison. It is found in trace amounts in the Earth's crust and is produced as a by-product of heavy metal sulfide ore smelting.
Properties
Period
6
Group
13
Block
P
Category
Post-Transition Metal
Electronegativity
1.62 (Pauling)
Ionization Energy
589.4 kJ/mol
Melting Point
577 K (304°C)
Boiling Point
1746 K (1473°C)
Density
11.85 g/cm³
Oxidation States
+1, +3
Electron Configuration
1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p¹
[Xe] 4f¹⁴ 5d¹⁰ 6s² 6p¹
Shell 1:2e⁻
Shell 2:8e⁻
Shell 3:18e⁻
Shell 4:32e⁻
Shell 5:18e⁻
Shell 6:3e⁻
Real-World Uses
Heart imaging (Tl-201)
Infrared detectors
Semiconductors
Low-temperature thermometers
Electronic components
Fun Fact
Thallium was called 'the poisoner's poison' because it's tasteless, colourless, and causes hair loss — making it the perfect murder weapon in detective novels!