Pauli and Hund: two different rules
Pauli’s exclusion principle limits orbital occupancy; Hund’s rule describes how equal-energy orbitals are filled.
Start with the idea
Pauli’s exclusion principle limits orbital occupancy; Hund’s rule describes how equal-energy orbitals are filled.
A concrete example
Across the three p orbitals, electrons first occupy available orbitals singly before pairing.
Mendeleev’s tip
Do not start with a formula. Identify what changes, what stays constant and which quantity you are trying to explain or calculate.
Go one step deeper
For nitrogen, the three 2p electrons occupy three separate p orbitals with parallel spins in the simplified ground-state picture.
A trend or model is not an exceptionless law. Always check the quantity’s definition and the conditions being compared.
Check your understanding
Can you explain the phenomenon in your own words before looking at an equation?