Which principle states that electrons fill the lowest available energy orbitals first?

Which principle states that electrons fill the lowest available energy orbitals first?

• A. Aufbau principle
• B. Hund's rule
• C. Pauli's Exclusion Principle
• D. Heisenberg Principle

Answer: (A)

Electrons fill the lowest available energy orbitals first. This ordering of filling is described by the Aufbau principle, which says electrons occupy orbitals starting with the lowest energy and progressively move to higher energies as needed. In practice, that means filling 1s first, then 2s, then 2p, then 3s, and so on, following the relative energies of the subshells. The nuance that 4s can be filled before 3d is part of how orbital energies are arranged for different elements. So, the principle that states electrons fill the lowest energy orbitals first is the Aufbau principle. Hund's rule concerns distributing electrons within a subshell to maximize unpaired spins, Pauli's Exclusion Principle restricts two electrons in an orbital to opposite spins, and Heisenberg's Principle relates to the uncertainty of simultaneously knowing position and momentum.

Electrons fill the lowest available energy orbitals first. This ordering of filling is described by the Aufbau principle, which says electrons occupy orbitals starting with the lowest energy and progressively move to higher energies as needed. In practice, that means filling 1s first, then 2s, then 2p, then 3s, and so on, following the relative energies of the subshells. The nuance that 4s can be filled before 3d is part of how orbital energies are arranged for different elements. So, the principle that states electrons fill the lowest energy orbitals first is the Aufbau principle. Hund's rule concerns distributing electrons within a subshell to maximize unpaired spins, Pauli's Exclusion Principle restricts two electrons in an orbital to opposite spins, and Heisenberg's Principle relates to the uncertainty of simultaneously knowing position and momentum.