Which principle governs the filling order of electrons into orbitals?

The filling order of electrons into orbitals is governed by the Aufbau principle. This principle states that electrons occupy the lowest energy orbitals first before moving into higher energy orbitals. The order in which orbitals are filled is determined by their increasing energy levels, which is often represented in a diagram known as the Aufbau diagram.

This filling order is crucial for predicting the electron configuration of an atom, which in turn helps understand the chemical properties and reactivity of the element. By following the Aufbau principle, one can correctly fill the orbitals for elements in the periodic table, beginning with the 1s orbital, followed by 2s, 2p, 3s, 3p, and so forth, based on their relative energies.

Other principles like Hund's rule and the Pauli exclusion principle play important roles in the behavior of electrons as well but focus on specific aspects such as maximizing electron spins in degenerate orbitals and ensuring that no two electrons in the same atom can have identical quantum numbers, respectively. Quantum theory encompasses broader concepts related to the behavior of particles at the atomic and subatomic levels, rather than providing specific guidelines for electron configuration.