81Tl204.380
Post-Transition Metalp-block
Thallium
Element 81 on the periodic table, symbol Tl, group 13, period 6.
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.
Appearance: silvery white
Properties
- Atomic Number
- 81
- Atomic Mass
- 204.3800 u
- Group
- 13
- Period
- 6
- Block
- p-block
- Category
- Post-Transition Metal
- State at 25 °C
- Solid
- Melting Point
- 577 K · 303.9 °C
- Boiling Point
- 1,746 K · 1,472.9 °C
- Density
- 11.85 g/cm³
- Atomic Radius
- 190 pm
- Electronegativity
- 1.62
- Oxidation States
- +1, +3
- Abundance in Crust
- 0.85 mg/kg
- Discovered
- 1861
- Discovered By
- William Crookes
Electron Configuration
[Xe] 4f14 5d10 6s2 6p1
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p1
Ionisation Energies (kJ/mol)
- 1. 589.4
- 2. 1,971
- 3. 2,878
Elements near Thallium
Elements in the same group share the number of outer electrons and behave in similar ways. Elements in the same period share a shell, so they change steadily from left to right.