Humber Admissions Practice Test

What does the Aufbau Principle state about electron filling in orbitals?

1. Electrons fill random orbitals

2. Electrons occupy the highest energy orbitals first

3. Electrons occupy the orbitals of lowest energy first

4. Electrons cannot fill orbitals of different energies

The correct answer is: Electrons occupy the orbitals of lowest energy first

The Aufbau Principle is a fundamental concept in atomic theory that describes the order in which electrons fill the orbitals of an atom. According to this principle, electrons will occupy the orbitals of lowest energy first before moving on to higher energy orbitals. This is crucial for determining the electron configuration of an atom, which ultimately influences its chemical properties and reactivity. This principle can be understood in the context of energy levels and stability; by filling the lowest energy orbitals first, atoms achieve a more stable electronic structure. As a result, when constructing the electron configuration for an element, one would begin with the 1s orbital, followed by the 2s, and so on, progressing to the higher energy levels only after the lower ones are filled. In contrast to the other potential answers, random filling of orbitals would result in an unstable and higher energy configuration, which does not reflect the natural tendency of electrons. Filling the highest energy orbitals first contradicts the Aufbau Principle, as it would mean moving to less stable arrangements before exhausting lower energy options. Lastly, the idea that electrons cannot fill orbitals of different energies misrepresents how electron distributions are achieved; while they typically fill lowest energies first, they can still occupy multiple energy levels once initial