Thallium (Tl): electron configuration, atomic mass and facts
Thallium (Tl) is element 81 of the periodic table, a post-transition metal in period 6, group 13. Its electron configuration is [Xe] 4f14 5d10 6s2 6p1, with electrons arranged in shells 2, 8, 18, 32, 18, 3, and its standard atomic weight is 204.38 u.
▶ Watch Thallium’s electrons orbit in the interactive periodic tableThallium at a glance
| Symbol | Tl |
|---|---|
| Atomic number | 81 |
| Atomic mass | 204.38 u |
| Category | Post-transition metal |
| Group | 13 |
| Period | 6 |
| Block | p-block |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s2 6p1 |
| Noble-gas shorthand | [Xe] 4f14 5d10 6s2 6p1 |
| Electrons per shell | 2, 8, 18, 32, 18, 3 |
| Outer-shell electrons | 3 |
| Electronegativity (Pauling) | 1.62 |
| State at 20 °C | solid |
Where is Thallium on the periodic table?
Thallium is in period 6, group 13, in the p-block. The period number matches its 6 electron shells, and the block names the subshell its last electrons fill. In the same group, Indium sits directly above it and Nihonium sits directly below it. Elements in one group have the same number of outer-shell electrons (3 here), which is why they react in similar ways.
How to work out the electron configuration of Thallium
Put 81 electrons into subshells in order of rising energy, filling each before starting the next: 1s² (2), 2s² (4), 2p⁶ (10), 3s² (12), 3p⁶ (18), 4s² (20), 3d¹⁰ (30), 4p⁶ (36), 5s² (38), 4d¹⁰ (48), 5p⁶ (54), 6s² (56), 4f¹⁴ (70), 5d¹⁰ (80), 6p¹ (81). In shorthand, [Xe] stands for the 54 electrons of xenon, giving [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p¹.
How electronegative is Thallium?
Thallium has a Pauling electronegativity of 1.62, ranking 49 of the 100 elements with a known value (fluorine is highest at 3.98). That is in the middle of the range.
Frequently asked questions
What is the electron configuration of Thallium?
The electron configuration of Thallium (Tl) is 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s2 6p1. In noble-gas shorthand it is written [Xe] 4f14 5d10 6s2 6p1.
How many electrons does Thallium have in each shell?
Thallium has 81 electrons arranged in shells as 2, 8, 18, 32, 18, 3. It has 3 electrons in its outer shell.
What is the atomic mass of Thallium?
The standard atomic weight of Thallium is 204.38 u, so one mole of Thallium atoms has a mass of about 204.38 g.
Is Thallium a metal?
Yes. Thallium is a post-transition metal.
Explore nearby elements
More post-transition metals: Indium, Tin, Lead, Bismuth, Polonium, Nihonium. See all elements on the periodic table.