Electron Pairing Rules

Pauli Exclusion Principle (Mac's)

In an atom or molecule, no two electrons can have the same four electronic quantum numbers. As an orbital can contain a maximum of only two electrons, the two electrons must have opposing spins.

Pauli Exclusion Principle

states that a maximum of two electrons can occupy a single atomic orbital but only if the electrons have opposite spins

Aufbau Principle

states that each electron occupies the lowest energy orbital available

Hund's Rule

states that single electrons with the same spin must occupy each equal-energy orbital before additional electrons with opposite spins can occupy the same orbitals

Aufbau Principle (Mac's)

Electrons will occupy the lowest E position available.

Hund's Rule (Mac's)

Every orbital in the same sublevel is singly occupied before any orbital is doubly occupied. All of the electrons in a singly occupied orbital have the same spin.