Definition
The Hund’s rule states, when assigning electrons to an atom, one electron is placed in each degenerate orbital first, before they are paired.
Explanation
To visualize Hund’s rule of electron assignment let’s consider the atoms Carbon, Nitrogen, and Oxygen. Each of these atoms has 6,7, and 8 electrons respectively that occupy orbitals 1s, 2s, and 2p. You should focus on the assignment in the degenerate p-orbitals as we move from Carbon towards Oxygen.
