According to the Pauli exclusion principle; No two electrons in an atom can have the same set of four quantum numbers.
Violation of the Pauli exclusion principle
The Pauli Exclusion Principle states that no two electrons can have the same four electronic quantum numbers in an atom or molecule. It states that an orbital can have a maximum of two electrons that must be of opposite spin. Thus, it was concluded that an orbital could have a maximum of two electrons that can have all 3-quantum number the same, but the spin will be definitely different.
- For the 1s subshell, the same orbital electrons have the same first three quantum numbers, e.g., n=1, l=0, m1=0.
- Only two electrons can have these numbers so that their spin moments must be either ms = -1/2 or ms = +1/2
- If the 1s orbital contains only one electron, we have one ms value, and the electron configuration is written as 1s1 (corresponding to hydrogen).
- But we will have two ms values if and only if it is fully occupied, and the electron configuration is 1s2(corresponding to helium).
- The 1s and 2s subshells for beryllium atoms can hold only two electrons, and when filled, the electrons must have opposite spins or have the same four quantum numbers. Thus violating the Pauli Exclusion Principle.