Electron Configuration of Thorium (Th)
Thorium (Th, Z = 90) has the electron configuration [Rn] 6d² 7s², filling 7 shells with 2, 8, 18, 32, 18, 10, 2 electrons.
Looking for Thorium's electron configuration without wading through a whole chapter? Here is the direct answer first, then the tables and derivations examiners want to see. Every number on this page comes from the same engine that powers the interactive table. Need the whole picture instead — history, characteristics, uses, exam questions? The full Thorium page is one click away.
Thorium: every subshell, one by one
Read the configuration like a receipt: each line is one subshell, and the running total climbs exactly to 90 electrons — never one more, never one less.
| Subshell | Electrons | Total so far |
|---|---|---|
| [Rn] | 0 | 86 |
| 6d | 2 | 88 |
| 7s | 2 | 90 |
Electrons per shell (K, L, M…)
Grouped by principal quantum number instead of subshell, Thorium carries 2 in shell 1, 8 in shell 2, 18 in shell 3, 32 in shell 4, 18 in shell 5, 10 in shell 6, 2 in shell 7. The outermost shell holds 2 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 90 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 Thorium that gives [Rn] 6d² 7s².
Note: Thorium is one of the textbook exceptions to strict aufbau filling — a half-filled or fully-filled d subshell buys extra stability, so its ground-state configuration is [Rn] 6d² 7s².
Students also ask
How many electron shells does Thorium have?
Thorium is in period 7, so its electrons occupy 7 shells, holding 2, 8, 18, 32, 18, 10, 2 electrons respectively.
How many valence electrons does Thorium have?
Its outermost shell holds 2 electrons, so Thorium has 2 valence electrons that take part in bonding.
What is the noble-gas shorthand for Thorium?
The shorthand form is exactly [Rn] 6d² 7s².