Atomic number 81
Thallium
Post-transition metal
In the real world
Quick facts
- Atomic mass
- 204.38
- Group
- 13
- Period
- 6
- State (STP)
- solid
- Electronegativity
- 1.62
- Common ox. states
- +1, +3
Properties
Electron configuration
[Xe] 4f¹⁴ 5d¹⁰ 6s² 6p¹
- Ionization energy
- 589.4 kJ/mol
- Electron affinity
- 36.4 kJ/mol
- Melting point
- 577.00 K (303.9 °C)
- Boiling point
- 1746.00 K (1472.8 °C)
How dangerous is it?
4/5 · Severe
Its compounds are colorless, tasteless, and slow-acting, which once made thallium a favorite hard-to-trace poison.
- ToxicImmediate and cumulative
It slips into the body in place of potassium and disrupts the nerves and organs. (its soluble compounds)
Handled with gloves in a fume hood and treated as hazardous waste.
How it bonds
Thallium is the textbook "inert pair effect" element: +1 is more stable than +3 (the 6s² electrons resist ionization). Tl⁺ mimics K⁺ in size, sneaks into potassium-using channels, and wreaks havoc - historically a famous poison.
