⬆️ FILLING ORBITALS
PAGE 1 OF 5, LOWEST ENERGY FIRST
AUFBAU
BUILD ATOMS FROM THE GROUND UP
The Aufbau principle says electrons fill the lowest available energy sub-shells first. You do not randomly place electrons. You follow an energy order such as 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, and so on. That order explains why potassium puts its outer electron in 4s, not 3d.
⬆️ AUFBAU
Aufbau means building up: fill lowest energy orbitals before higher ones.
FILL!
START LOW
1️⃣ Begin at 1s
⬆️ Climb the energy ladder step by step
📋 Order follows sub-shell energies
⬆️ Climb the energy ladder step by step
📋 Order follows sub-shell energies
EXAMPLE
🧪 K is [Ar] 4s¹ not 3d¹
🎯 Predictable configurations
📊 Energy beats simple shell number
🎯 Predictable configurations
📊 Energy beats simple shell number