081Post-transition metal · Group 13 · Period 6
Thallium
Thallium (Tl) is element 81, a post-transition metal in the p-block — group 13, period 6. It is a solid at room temperature with 6 electron shells (2, 8, 18, 32, 18, 3) and an atomic mass of 204.38 u.
- Atomic mass
- 204.4 u
- Phase · STP
- solid
- Melting
- 577 K · 304 °C
- Boiling
- 1746 K · 1473 °C
- Electronegativity
- 1.62
- Density
- 11.85 g/cm³
Photograph — Hi-Res Images ofChemical Elements, CC BY 3.0 <https://creativecommons.org/licenses/by/3.0>, via Wikimedia Commons, source: https://images-of-elements.com/thallium.php
Identity
- Atomic number
- 81
- Standard atomic weight
- 204.4 u
- Category
- Post-transition metal
- Group
- 13
- Period
- 6
- Block
- p-block
- Oxidation states
- +3, +1
Physical properties
- Melting point
- 577 K · 304 °C
- Boiling point
- 1746 K · 1473 °C
- Density
- 11.85 g/cm³
- Molar heat capacity
- 26.32 J/(mol·K)
- Atomic radius
- 196 pm
- Electron affinity
- 36.4 kJ/mol
Atomic structure
81protons
123neutrons
81electrons
3valence e⁻
- Noble-gas notation
- [Xe] 4f14 5d10 6s2 6p1
- Full configuration
- 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p1
- Electrons per shell
- 2, 8, 18, 32, 18, 3
Periodic trends
Where Thallium ranks across all 118 elements.
Ionization energies
Energy to remove each successive electron (kJ/mol).
589.41
2.0k2
2.9k3
Successive ionization energies (kJ/mol, log scale).
Discovery
- Discovered
- 1861
- Discovered by
- William Crookes
- Named by
- —
- Appearance
- silvery white