Electron Configuration Rules

Question 1

Aufbau Principle

Answer 1

Electrons fill orbitals from lowest to highest energy. Order: 1s → 2s → 2p → 3s → 3p → 4s → 3d → 4p → 5s …

Question 2

Pauli Exclusion Principle

Answer 2

No two electrons can have the same four quantum numbers. Each orbital holds a maximum of 2 electrons with opposite spins (↑↓).

Question 3

Hund’s Rule

Answer 3

Electrons fill orbitals singly with parallel spins before pairing up.

“Sit alone on the bus before doubling up.”