Aufbau Principle
A rule governing electron configuration stating that electrons fill atomic orbitals of lower energy levels before occupying higher energy levels.
Governing formula
Order: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s...
SI unit
Dimensionless Rule
In depth
Derived from the German word for 'building up', the Aufbau principle builds the periodic table structure by systematically adding electrons to the lowest available energy sublevels determined by the (n + l) energy ordering rule.
Examples in the real world
Carbon (Z=6) establishing an electron configuration of 1s² 2s² 2p² in its ground state.