Electron Configuration of Magnesium (Mg)
Magnesium (Mg, Z = 12) has the electron configuration [Ne] 3s^2, filling 3 shells with 2, 8, 2 electrons.
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Magnesium: every subshell, one by one
Read the configuration like a receipt: each line is one subshell, and the running total climbs exactly to 12 electrons — never one more, never one less.
| Subshell | Electrons | Total so far |
|---|---|---|
| [Ne] | 0 | 10 |
| 3s | 2 | 12 |
Electrons per shell (K, L, M…)
Grouped by principal quantum number instead of subshell, Magnesium carries 2 in shell 1, 8 in shell 2, 2 in shell 3. 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 12 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 Magnesium that gives [Ne] 3s^2.
Students also ask
How many electron shells does Magnesium have?
Magnesium is in period 3, so its electrons occupy 3 shells, holding 2, 8, 2 electrons respectively.
How many valence electrons does Magnesium have?
Its outermost shell holds 2 electrons, so Magnesium has 2 valence electrons that take part in bonding.
What is the noble-gas shorthand for Magnesium?
The shorthand form is exactly [Ne] 3s^2.