Thallium
A soft, highly toxic metal once used in rat poison.
Inside the Thallium atom
Switch between Bohr and Quantum Cloud modes to compare a simple teaching model with a more realistic probability-based view, and follow the guided tour to explore the Thallium atom step by step.
Electron configuration
[Xe] 4f14 5d10 6s2 6p1
A neutral Thallium atom has 81 electrons (equal to its proton count). Choosing a different isotope above changes only the neutron count.
Shell distribution
Electrons fill inner shells before outer ones; the outermost (valence) shell drives the element's chemistry.
Physical & atomic properties
- State (room temp)
- Solid
- Melting point
- 577 K (304 °C)
- Boiling point
- 1746 K (1473 °C)
- Density
- 11.85 g/cm³
- Electronegativity
- 1.62 Pauling
- Atomic radius
- 190 pm
- 1st ionization energy
- 589 kJ/mol
- Category
- Post-transition metals
Discovery & naming
- Discovered
- 1861
- Discovered by
- William Crookes
- Origin of name
- Greek 'thallos', meaning a green shoot.
Notable uses
Electronics, infrared detectors, and (historically) rat poison.
Where Thallium comes from
Several comparable sources
Both slow neutron capture in dying stars and rapid capture in explosive events contribute meaningfully.
Simplified origin map — many elements form through more than one astrophysical pathway.
Summary
- Atomic number
- 81
- Atomic mass
- 204.38
- Category
- Post-transition metals
- Group · Period
- 13 · 6
- Block
- p-block
- Shells
- 2 · 8 · 18 · 32 · 18 · 3