Electron configuration
Choose an element to see its reference and expanded electron configuration, shell counts, subshells and orbital occupancy.
Useful examples
Electron configuration
Electrons by principal shell (n)
electrons unpaired arrows
Orbital diagram
Each box is one orbital; arrows are electrons with opposite spin when paired. Boxes show occupancy, not electron paths around the nucleus.
Filling order
The Madelung sequence is a useful construction rule, not an inviolable law. Real ground states can differ when subshell energies are close.
Three rules behind the boxes
Pauli exclusion
An orbital holds at most two electrons, and a paired set has opposite spin.
Hund’s rule
Within p, d or f subshells, electrons occupy separate orbitals before they pair.
Madelung order
Lower n + ℓ is filled first; when tied, lower n comes first. Real atoms can depart from this simple ordering.