Periodic Table
81
Tl
204.38
Thallium
Post-transitionInert pair effect — +1 more stable than +3; toxic.
Electronic Configuration
[Xe] 4f¹⁴ 5d¹⁰ 6s² 6p¹or1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 4f¹⁴ 5d¹⁰ 6s² 6p¹
Electron shells
2e⁻n=1
8e⁻n=2
18e⁻n=3
32e⁻n=4
18e⁻n=5
3e⁻n=6
Properties
Atomic number
81
Atomic mass
204.38 u
Category
Post-transition
Block / Group / Period
p · 13 · 6
Valence electrons
3
Oxidation states
+1, +3
Electronegativity
1.62
Atomic radius
156 pm
Ionization energy
589 kJ/mol
Electron affinity
19 kJ/mol
Melting point
577 K / 304 °C
Boiling point
1746 K / 1473 °C
Density
11.85 g/cm³
State at 25 °C
solid
Personal Notes
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