1. The problem statement, all variables and given/known data Discuss the evidence from the periodic table of the need for a fourth quantum number. How would the properties of He differ if there were only three quantum numbers, n, l, and m? 2. Relevant equations 3. The attempt at a solution The Pauli Exclusion Principle dictates that no two electrons can occupy exactly the same orbital configuration. If there was no fourth quantum number, atoms with the same n,l, and m, would be smaller.