Electron Configuration of Molybdenum (Mo)
Molybdenum (Mo, Z = 42) has the electron configuration [Kr] 4d⁵ 5s¹, filling 5 shells with 2, 8, 18, 13, 1 electrons.
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Molybdenum: every subshell, one by one
Read the configuration like a receipt: each line is one subshell, and the running total climbs exactly to 42 electrons — never one more, never one less.
| Subshell | Electrons | Total so far |
|---|---|---|
| [Kr] | 0 | 36 |
| 4d | 5 | 41 |
| 5s | 1 | 42 |
Electrons per shell (K, L, M…)
Grouped by principal quantum number instead of subshell, Molybdenum carries 2 in shell 1, 8 in shell 2, 18 in shell 3, 13 in shell 4, 1 in shell 5. The outermost shell holds 1 electron — the ones that do all the bonding.
How to derive it yourself
Follow the aufbau order (1s → 2s → 2p → 3s → 3p → 4s → 3d → …), pouring 42 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 Molybdenum that gives [Kr] 4d⁵ 5s¹.
Note: Molybdenum 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 [Kr] 4d⁵ 5s¹.
Students also ask
How many electron shells does Molybdenum have?
Molybdenum is in period 5, so its electrons occupy 5 shells, holding 2, 8, 18, 13, 1 electrons respectively.
How many valence electrons does Molybdenum have?
Its outermost shell holds 1 electron, so Molybdenum has 1 valence electron that take part in bonding.
What is the noble-gas shorthand for Molybdenum?
The shorthand form is exactly [Kr] 4d⁵ 5s¹.