Electron configuration

Distribution of electrons in each orbital governed by three rules

• Aufbau Principle

Charging electrons into each orbital / suborbital adapted to different levels of energy of each orbital

For example: ²⁰Ca : 1s² 2s² 2p⁶ 3s² 3p⁶ 4s²

•    Pauli Exclusion Principle

Each electron in the atoms just have 1 four quantum numbers (n, l, m and z), if n, l, m equals then s must be different.

Order of orbitals (filling) in multi-electron atom

1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p < 6s

Fill lowest energy orbitals first (Aufbau principle)

Fill lowest energy orbitals first (Aufbau principle)

Fill lowest energy orbitals first (Aufbau principle)

• .    Hund’s Rule

Charging an electron into the orbital / sub-orbital which has the equivalent energy levels may not form the pair first, before orbital who have similar levels of energy that filled half

full.

 For example: ₈O:1s² 2s² 2p_x² 2p_y¹ 2p_z¹

Hund’s rule: The most stable arrangement of electrons in subshells is the one with the greatest number of parallel spins.