Humber Admissions Practice Test

What principle dictates that electrons will occupy the lowest available energy level first?

1. Hund's rule

2. Pauli Exclusion Principle

3. Aufbau Principle

4. Ionic Theory

The correct answer is: Aufbau Principle

The correct answer is the principle that states electrons will occupy the lowest available energy level first. This is known as the Aufbau Principle. According to this principle, electrons fill atomic orbitals in order of increasing energy levels, which means that they will first occupy the lowest energy orbitals before moving to higher energy levels. This prioritization in the filling of electron orbitals enables an atom to attain a more stable, lower-energy state. When electrons are added to an atom, they do so by filling the closest, energy-minimized orbitals available, thereby adhering to this principle. In contrast, the other principles mentioned do not align with this specific directive; Hund's rule pertains to the distribution of electrons in degenerate orbitals, indicating that electrons will occupy separate orbitals before pairing up in the same orbital. The Pauli Exclusion Principle states that no two electrons can have identical sets of quantum numbers within an atom but does not dictate the order of filling orbitals. Ionic Theory discusses the behavior of ions in solutions and does not relate directly to the structure of electron shells or energy levels.