Thallium (Tl) - Element 81 | Properties & Electron Configuration
What is Thallium?
Thallium (Tl) is element 81, a post transition metal in period 6, group 13. Its electron configuration is 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p¹.
| Atomic Number | 81 |
| Symbol | Tl |
| Atomic Mass | 204.38 u |
| Category | Post Transition Metal |
| Period | 6 |
| Group | 13 |
| Block | p |
| Electron Configuration | 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p¹ |
| Short Config | [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p¹ |
| Electronegativity | 1.62 |
| Atomic Radius | 190 pm |
| Ionization Energy | 589 kJ/mol |
| Electron Affinity | 19 kJ/mol |
| Phase (STP) | Solid |
Electron Configuration
The full electron configuration of Thallium is 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p¹. In noble gas shorthand, this is written as [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p¹.
Thallium is a p-block element in group 13, period 6.
Periodic Trends
Electronegativity: Thallium has a Pauling electronegativity of 1.62. Within group 13, electronegativity generally decreases down the group.
Atomic Radius: 190 pm. Across period 6, atomic radius generally decreases left to right as nuclear charge increases.
Ionization Energy: 589 kJ/mol. Ionization energy generally increases across a period and decreases down a group.
View all 118 elements with trend overlays for electronegativity, atomic radius, ionization energy, and electron affinity.
Explore Thallium on the Interactive Periodic TableRelated Topics
Boron (B)
Properties of Boron - same group as Thallium
Aluminum (Al)
Properties of Aluminum - same group as Thallium
Gallium (Ga)
Properties of Gallium - same group as Thallium
Cesium (Cs)
Properties of Cesium - same period as Thallium
Barium (Ba)
Properties of Barium - same period as Thallium
Lanthanum (La)
Properties of Lanthanum - same period as Thallium