Which principle states that each suborbital fills with one electron before pairing?

Hund's Rule is the principle that states that each suborbital within a given energy level or subshell will fill with one electron before any pairing of electrons occurs. This means that when you have multiple orbitals of the same energy level, such as the three p orbitals or the five d orbitals, you first place one electron in each orbital to maximize the number of unpaired electrons, which minimizes electron-electron repulsion and helps stabilize the atom.

This principle is crucial in understanding the behavior of electrons in an atom and their contributions to chemical bonding, as the spatial arrangement of electrons influences how atoms interact with each other. In contrast, the Aufbau Principle describes the process of filling electrons into orbitals starting from the lowest energy level before moving to higher levels. The Octet Rule relates to the tendency of atoms to seek a full outer shell of electrons, typically eight, when forming bonds. The Pauli Exclusion Principle states that no two electrons can have the same set of four quantum numbers, which explains why an orbital can hold a maximum of two electrons only if they have opposite spins.