Electron Configuration Builder
Watch electrons fill orbitals following the Aufbau principle, Hund's rule, and the Pauli exclusion principle.
26 Fe
Fe26 e⁻
Iron
1s2 2s2 2p6 3s2 3p6 4s2 3d6
1s2/2
↑↓
ml=+0
2s2/2
↑↓
ml=+0
2p6/6
↑↓
↑↓
↑↓
ml=-1ml=+0ml=+1
3s2/2
↑↓
ml=+0
3p6/6
↑↓
↑↓
↑↓
ml=-1ml=+0ml=+1
4s2/2
↑↓
ml=+0
3d6/10
↑↓
↑
↑
↑
↑
ml=-2ml=-1ml=+0ml=+1ml=+2
Subshells:s (max 2e⁻)p (max 6e⁻)d (max 10e⁻)f (max 14e⁻)↑↓ = spin-up/spin-down electron pair
Aufbau Principle
Electrons fill lowest energy orbitals first: 1s → 2s → 2p → 3s → 3p → 4s → 3d ...
Hund's Rule
Within a subshell, electrons fill each orbital singly (same spin) before pairing up.
Pauli Exclusion
Each orbital holds at most 2 electrons with opposite spins (↑↓).