What is Hund’s rule of multiplicity

Hund’s rule of multiplicity states that electrons fill degenerate orbitals singly before pairing up, and all unpaired electrons have parallel spins.

Degenerate orbitals are orbitals with the same energy, such as the three p-orbitals or five d-orbitals. According to Hund’s rule, electrons prefer to occupy empty orbitals of equal energy one by one rather than pair up in the same orbital. This arrangement minimizes repulsion and increases stability.

Example

For the carbon atom (atomic number 6):

• Electronic configuration: 1s² 2s² 2p²
• According to Hund’s rule: The two electrons in the 2p subshell occupy separate orbitals with parallel spins (↑ ↑).

Importance

• Explains the structure of atomic orbitals.
• Used to predict magnetic properties of elements (paramagnetism or diamagnetism).
• Helps in writing correct electronic configurations.