81TlThallium204.38[Xe] 4f¹⁴ 5d¹⁰ 6s² 6p¹
post-transition metal
Thallium
Thallium is a chemical element with symbol Tl and atomic number 81. This soft gray post-transition metal is not found free in nature. When isolated, it resembles tin, but discolors when exposed to air.
A stylized shell model. Electrons are quantum objects, not particles following these literal paths. Sizes and motion are illustrative.
Electrons by shell
Electron configuration
4f14
5d10
6s2
6p1
54 is the [Xe] core total across five shells.
At a glance
- Atomic number
- 81
- Atomic mass
- 204.38 u
- Phase
- Solid
- Density
- 11.85 g/cm³
- Melting point
- 577 K
- Boiling point
- 1,746 K
- First ionization energy
- 589.4 kJ/mol
- Electronegativity
- 1.62
- Electron affinity
- 36.4 kJ/mol
- Molar heat capacity
- 26.32 J/(mol·K)
- Period
- 6
- Appearance
- silvery white
Conditions and isotopes affect measured properties. Some properties of short-lived elements are predicted. Electronegativity uses the Pauling scale.
Keep exploring
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