Electron Configuration of Arsenic (As)
Arsenic (As, Z = 33) has the electron configuration [Ar] 3d^10 4s^2 4p^3, filling 4 shells with 2, 8, 18, 5 electrons.
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Arsenic: every subshell, one by one
Read the configuration like a receipt: each line is one subshell, and the running total climbs exactly to 33 electrons — never one more, never one less.
| Subshell | Electrons | Total so far |
|---|---|---|
| [Ar] | 0 | 18 |
| 3d | 10 | 28 |
| 4s | 2 | 30 |
| 4p | 3 | 33 |
Electrons per shell (K, L, M…)
Grouped by principal quantum number instead of subshell, Arsenic carries 2 in shell 1, 8 in shell 2, 18 in shell 3, 5 in shell 4. The outermost shell holds 5 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 33 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 Arsenic that gives [Ar] 3d^10 4s^2 4p^3.
Students also ask
How many electron shells does Arsenic have?
Arsenic is in period 4, so its electrons occupy 4 shells, holding 2, 8, 18, 5 electrons respectively.
How many valence electrons does Arsenic have?
Its outermost shell holds 5 electrons, so Arsenic has 5 valence electrons that take part in bonding.
What is the noble-gas shorthand for Arsenic?
The shorthand form is exactly [Ar] 3d^10 4s^2 4p^3.