What is the Pauli exclusion principle? Why is it important when writing electron configurations?
Pauli Exclusion Principle states that “ no two electrons in an atom can have can have the same four electronic quantum numbers.”
Therefore, two electrons present in the same orbital having same n, l and ml but both the electrons should have opposite spin(ms).Thus, each orbital can have a maximum of only two electrons, with opposing spins( ms=- ½ and ms=+½ ).
The electron configuration of an atom is the representation of the arrangement of electrons distributed among the orbital shells and subshells.
According to Pauli’s Principle, two electrons occupying in a same orbital should have opposite spin, otherwise they would have the same four quantum numbers, which is forbidden.