81Tl204.38
Thallium (Tl)
Element 81 · Post-transition metal
Thallium (Tl) is a chemical element with atomic number 81. It is classified as a post-transition metal in period 6, group 13 of the periodic table (the p-block). Its standard atomic weight is 204.38 u and its ground-state electron configuration is [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p¹.
Thallium facts
| Atomic number (Z) | 81 |
|---|---|
| Symbol | Tl |
| Standard atomic weight | 204.38 u |
| Category | Post-transition metal |
| Group | 13 |
| Period | 6 |
| Block | p-block |
| Electron configuration | [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p¹ |
| Electronegativity (Pauling) | 1.62 |
| State at 20 °C | Solid |
| Protons / electrons | 81 / 81 |
| Neutrons (most common isotope, approx.) | 123 |
| Molar mass | 204.38 g/mol |