Which statement best describes the overall filling of electron configurations according to common principles?

Which statement best describes the overall filling of electron configurations according to common principles?

• A. Electrons fill energy levels in order of increasing energy, following Aufbau, Hund's, and Pauli principles
• B. Electrons fill higher-energy orbitals before lower-energy ones
• C. All electrons in a subshell pair up before moving to the next subshell
• D. Electron spin has no effect on orbital filling

Answer: (A)

Electrons fill orbitals by increasing energy, not by skipping to higher energy levels. This ordering comes from the Aufbau principle, which describes how electrons are added to the lowest available energy states first. When multiple orbitals have the same energy, Hund’s rule says to place one electron in each degenerate orbital before any pairing occurs, maximizing the number of unpaired spins. The Pauli exclusion principle then limits each orbital to at most two electrons with opposite spins, preventing two electrons from sharing the same set of quantum numbers. Together, these rules explain the full pattern of electron filling, matching the statement that describes filling in order of increasing energy while applying Aufbau, Hund’s, and Pauli principles. The other options contradict these rules: electrons don’t fill higher-energy orbitals first, subshells aren’t always filled by pairing before moving on, and electron spin does influence orbital filling.

Electrons fill orbitals by increasing energy, not by skipping to higher energy levels. This ordering comes from the Aufbau principle, which describes how electrons are added to the lowest available energy states first. When multiple orbitals have the same energy, Hund’s rule says to place one electron in each degenerate orbital before any pairing occurs, maximizing the number of unpaired spins. The Pauli exclusion principle then limits each orbital to at most two electrons with opposite spins, preventing two electrons from sharing the same set of quantum numbers. Together, these rules explain the full pattern of electron filling, matching the statement that describes filling in order of increasing energy while applying Aufbau, Hund’s, and Pauli principles. The other options contradict these rules: electrons don’t fill higher-energy orbitals first, subshells aren’t always filled by pairing before moving on, and electron spin does influence orbital filling.