What principle states that as sublevels are filled, each orbital receives one electron before any orbital is filled with two?

The principle that states each orbital in a given sublevel receives one electron before any orbital is filled with a second electron is known as Hund's rule. This rule emphasizes that electrons will occupy degenerate orbitals (orbitals of the same energy) singly and with parallel spins to minimize electron-electron repulsion and maximize total spin.

This approach leads to a more stable arrangement of electrons within an atom because it allows for the highest possible total spin multiplicity. For example, in the case of the p sublevel, which has three degenerate orbitals, Hund's rule dictates that one electron will occupy each of the three orbitals singly before pairing begins, leading to a situation where each electron can claim its own space and there are fewer repulsive interactions.

In contrast, other principles related to electron configuration serve different purposes. The Aufbau principle outlines the order in which sublevels are filled with electrons based on increasing energy levels, while the Pauli exclusion principle states that no two electrons in an atom can have the same set of four quantum numbers, meaning an orbital can hold a maximum of two electrons with opposite spins. The quantum mechanical model describes the behavior of electrons in atoms but does not specifically deal with the filling order of orbitals.