Question

Define Pauli's exclusion principle and why is it called exclusion principle?

Answer 1

Pauli's Exclusion principle:

• Pauli exclusion principle states that no two electrons will have an identical set or the same quantum numbers (n, l, m, and s).
• For example, in a helium atom, the atom has 2 bound electrons and they occupy the outermost shell with opposite spins. Here, we will find that the two electrons are in the 1s subshell where n = 1, l = 0, and m= 0.
• Their spin moments will also be different. One will be s = -1/2 and the other will be +1/2.

• There are two salient rules that the Pauli exclusion principle follows:
• Only two electrons can occupy the same orbital.
• The two electrons that are present in the same orbital must have opposite spins, or they should be antiparallel.

It is called the exclusion principle because, according to this principle, if one electron in an atom has the same particular values for the four quantum numbers, then all the other electrons in that atom are excluded from having the same set of values.