Electron Configurations

The way electrons are arranged in atoms

Energy Levels (Principle Quantum Number – n) First energy level ◦ Only s sublevel (1 s orbital) ◦ Only 2 electrons ◦ 1s 2 Second energy level ◦ s and p sublevels (2s and 2p orbitals) ◦ 2 in s, 6 in p ◦ 2s 2 2p 6 ◦ 8 total electrons

Energy Levels (Principle Quantum Number – n) third energy level ◦ s, p, and d orbitals ◦ 2 in s, 6 in p, and 10 in d ◦ 3s 2 3p 6 3d 10 ◦ 18 total electrons fourth energy level ◦ S, p, d, and f orbitals ◦ 2 in s, 6 in p, 10 in d, 14 in f ◦ 4s 2 4p 6 4d 10 4f 14 ◦ 32 total electrons

Energy Level Diagram

Electron filling AUFBAU PRINCIPLE – electrons enter the lowest energy first PAULI EXCLUSION PRINCIPLE – 2 electrons per orbital ◦ must have different spins (shown using arrows) HUND’S RULE – when electrons occupy orbitals of equal energy they don’t pair up until they have to.

Order of Filling

Example 1: Oxygen Electron Configuration: 1s 2 2s 2 2p 4 Abbreviated EC: [He]2s 2 2p 4

Example 2: Aluminum Electron Configuration: 1s 2 2s 2 2p 6 3s 2 3p 1 Abbreviated EC: [Ne]3s 2 3p 1

Valence Orbitals