Electron Configuration of Thallium (Tl)
Thallium (Tl, Z = 81) has the electron configuration [Xe] 4f^14 5d^10 6s^2 6p^1, filling 6 shells with 2, 8, 18, 32, 18, 3 electrons.
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Thallium: every subshell, one by one
Read the configuration like a receipt: each line is one subshell, and the running total climbs exactly to 81 electrons — never one more, never one less.
| Subshell | Electrons | Total so far |
|---|---|---|
| [Xe] | 0 | 54 |
| 4f | 14 | 68 |
| 5d | 10 | 78 |
| 6s | 2 | 80 |
| 6p | 1 | 81 |
Electrons per shell (K, L, M…)
Grouped by principal quantum number instead of subshell, Thallium carries 2 in shell 1, 8 in shell 2, 18 in shell 3, 32 in shell 4, 18 in shell 5, 3 in shell 6. The outermost shell holds 3 electrons — the ones that do all the bonding.
How to derive it yourself
Follow the aufbau order (1s → 2s → 2p → 3s → 3p → 4s → 3d → …), pouring 81 electrons into orbitals of capacity 2 (s), 6 (p), 10 (d) and 14 (f) until none remain. Write the filled inner shells as the nearest noble-gas core — for Thallium that gives [Xe] 4f^14 5d^10 6s^2 6p^1.
Students also ask
How many electron shells does Thallium have?
Thallium is in period 6, so its electrons occupy 6 shells, holding 2, 8, 18, 32, 18, 3 electrons respectively.
How many valence electrons does Thallium have?
Its outermost shell holds 3 electrons, so Thallium has 3 valence electrons that take part in bonding.
What is the noble-gas shorthand for Thallium?
The shorthand form is exactly [Xe] 4f^14 5d^10 6s^2 6p^1.