What is Hund's rule of multiplicity?

Hund's rule of multiplicity

• This rule states that the “pairing of electrons in the orbitals belonging to the same subshell (p, d or f) does not take place until each orbital belonging to that subshell has got one electron each i.e., it is singly occupied.”

Example

• In the case of p-subshell(which consists of 3 orbitals ), pairing occurs with the entry of the 4th electron.
• In the case of the d-subshell(which consists of 5 orbitals), pairing occurs with the entry of the 6th electron.
• In the case of f -subshell(which consists of 7 orbital), pairing occurs with the entry of the 8th electron.