Predicting Electronic Configuration

Pauli Exclusion Principle and Hund's RuleThe Pauli exclusion principle states that two electrons may occupy the same orbital only if they have opposite spins.Hund's rule states that electrons occupy orbitals of the same energy singly before pairing.The 4s orbital has a lower energy than the 3d orbitals, so the 4s orbital is filled before the 3d orbitals.The lowest energy orbitals are filled first.Each orbital can accommodate two electrons.The exact energy of the electron is determined by the number of protons and the repulsion of the inner shell electrons so there are exceptions to the general rule.potassium1s² 2s² 2p⁶ 3s² 3p⁶4s¹chromium1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d⁵copper1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d¹⁰