Chemical element · Atomic number 81
Thallium
Thallium in the periodic table: atomic number 81, electron configuration, atomic mass, physical data, oxidation states, media credit and visible sources.
Post-transition metal
solid
204.383 u
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Atomic classification
Shell occupancy
Thallium in the Bohr shell model
This shows the electron distribution of the neutral atom in a simplified shell model.
- K · n=1
- 2 electrons
- L · n=2
- 8 electrons
- M · n=3
- 18 electrons
- N · n=4
- 32 electrons
- O · n=5
- 18 electrons
- P · n=6
- 3 electrons
- Electron configuration
- [Xe]6s2 4f14 5d10 6p1
- Electrons per shell
- 2 · 8 · 18 · 32 · 18 · 3
- Group
- 13
- Period
- 6
- Block
- P
- Element category
- Post-transition metal
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Physical and chemical properties
- Atomic mass
- 204.383 u
- Standard state
- solid
- Density
- 11.8 g/cm³
- Melting point
- 577 K
- Boiling point
- 1,746 K
- Electronegativity
- 1.62 (Pauling)
- First ionisation energy
- 6.108 eV
- Oxidation states
- +3, +1
- Discovery
- 1861
Safety and periodic classification
Safety
Safe handling cannot be inferred from Thallium's position in the periodic table alone. Laboratory, classroom and disposal decisions must follow the documentation for the exact material and its safety data sheet.
Position and comparison
Thallium is in period 6, group 13 and the P block. Its direct neighbours by atomic number are Mercury and Lead. The recorded Pauling electronegativity is 1.62. Periodic trends are compared only through the separately sourced neighbouring values.
Sources and scope
PubChem attributes element data to sources including IUPAC, NIST and IAEA. Quanta stores the referenced snapshot locally and leaves unknown values unavailable.