Skip to content
Physics

Electron Configuration

Explore how electrons fill atomic orbitals and build an element's electron configuration.
Source codeExternal Link Icon

Pick An Element

Oxygen selected, atomic number 8.

Element

OOxygen

Atomic Notation

Oxygen with mass number 16 and atomic number 8.

Proton
8
Electron
8
Neutron
8

Electron configuration

1s² 2s² 2p⁴

  • K shell
  • L shell

Shell distribution

  • K2
  • L6

Quantum numbers for the last electron

Selected state2p↓
(n, ℓ, m, s)(2,1,−1,−12)(2, 1, -1, -\frac{1}{2})

Electron Orbital in 3D

Explore the occupied orbitals of Oxygen. Shaded lobes show their characteristic shapes; the dots show sampled electron probability.

Occupied subshell

Orbital orientation

Oxygen: 2p orbital, orientation 1 of 3, 2 electrons
2p · orientation 1 · 2 e⁻

Aufbau Diagram

Follow the filling-order path

  1. 1s
  2. 2s
  3. 2p
  4. 3s
  5. 3p
  6. 4s
  7. 3d
  8. 4p
  9. 5s
  10. 4d
  11. 5p
  12. 6s
  13. 4f
  14. 5d
  15. 6p
  16. 7s
  17. 5f
  18. 6d
  19. 7p
Shell 1
1s subshell, filling order 1, 2 electrons. m 0: 2 electrons.
Shell 2
2s subshell, filling order 2, 2 electrons. m 0: 2 electrons.
2p subshell, filling order 3, 4 electrons. m −1: 2 electrons, m 0: 1 electron, m +1: 1 electron. Contains the last electron.
Shell 3
3s subshell, filling order 4, 0 electrons. m 0: 0 electrons.
3p subshell, filling order 5, 0 electrons. m −1: 0 electrons, m 0: 0 electrons, m +1: 0 electrons.
3d subshell, filling order 7, 0 electrons. m −2: 0 electrons, m −1: 0 electrons, m 0: 0 electrons, m +1: 0 electrons, m +2: 0 electrons.
Shell 4
4s subshell, filling order 6, 0 electrons. m 0: 0 electrons.
4p subshell, filling order 8, 0 electrons. m −1: 0 electrons, m 0: 0 electrons, m +1: 0 electrons.
4d subshell, filling order 10, 0 electrons. m −2: 0 electrons, m −1: 0 electrons, m 0: 0 electrons, m +1: 0 electrons, m +2: 0 electrons.
4f subshell, filling order 13, 0 electrons. m −3: 0 electrons, m −2: 0 electrons, m −1: 0 electrons, m 0: 0 electrons, m +1: 0 electrons, m +2: 0 electrons, m +3: 0 electrons.
Shell 5
5s subshell, filling order 9, 0 electrons. m 0: 0 electrons.
5p subshell, filling order 11, 0 electrons. m −1: 0 electrons, m 0: 0 electrons, m +1: 0 electrons.
5d subshell, filling order 14, 0 electrons. m −2: 0 electrons, m −1: 0 electrons, m 0: 0 electrons, m +1: 0 electrons, m +2: 0 electrons.
5f subshell, filling order 17, 0 electrons. m −3: 0 electrons, m −2: 0 electrons, m −1: 0 electrons, m 0: 0 electrons, m +1: 0 electrons, m +2: 0 electrons, m +3: 0 electrons.
Shell 6
6s subshell, filling order 12, 0 electrons. m 0: 0 electrons.
6p subshell, filling order 15, 0 electrons. m −1: 0 electrons, m 0: 0 electrons, m +1: 0 electrons.
6d subshell, filling order 18, 0 electrons. m −2: 0 electrons, m −1: 0 electrons, m 0: 0 electrons, m +1: 0 electrons, m +2: 0 electrons.
Shell 7
7s subshell, filling order 16, 0 electrons. m 0: 0 electrons.
7p subshell, filling order 19, 0 electrons. m −1: 0 electrons, m 0: 0 electrons, m +1: 0 electrons.

The numbers and arrows show filling order. The blue subshell contains the last electron. The m value appears above each orbital box; ↑↓ is a pair of electrons with opposite spins.

Vocabulary

Symbols used on this page

Electron configuration and quantum-number vocabulary
SymbolTermMeaningExample
ZAtomic numberThe number of protons in the nucleus. For a neutral atom, it also equals the number of electrons.Oxygen: Z = 8
nPrincipal (shell) quantum numberThe electron shell or main energy level, numbered from 1 to 7.n = 1 is the K shell
ℓAzimuthal (subshell) quantum numberThe subshell and general orbital shape within a shell.s = 0, p = 1, d = 2, f = 3
mMagnetic quantum numberThe specific orbital orientation inside a subshell.For p: −1, 0, +1
sSpin quantum numberThe spin direction of an electron.+½ or −½
K–QShell namesLetter names for the seven electron shells.K (n = 1), L (n = 2), …, Q (n = 7)
s, p, d, fSubshellsThe four subshell types, each containing a different number of orbitals.Maximum: 2, 6, 10, and 14 electrons
□OrbitalA region that can hold at most two electrons with opposite spins.One box in the Aufbau diagram
↑ / ↓Electron arrowsElectrons and their spin directions inside an orbital.↑↓ is a paired orbital
2p⁴Electron configurationA compact description of how an atom's electrons occupy its subshells.2p⁴ = four electrons in the 2p subshell
AufbauFilling principleThe principle that lower-energy orbitals fill before higher-energy orbitals.1s → 2s → 2p → 3s
NeutralNeutral atomAn atom whose proton and electron counts are equal, giving no net charge.8 protons and 8 electrons
Ground stateGround-state configurationThe lowest-energy electron arrangement of an atom.The configuration shown by this page