The Aufbau principle is a fundamental concept in chemistry that describes the order in which electrons fill atomic orbitals. According to this principle, electrons occupy the lowest energy orbitals first before moving to higher energy levels. This helps to determine the electron configuration of an atom, which is crucial for understanding its chemical properties. In practice, the Aufbau principle is often illustrated using the electron configuration notation, where orbitals are filled in a specific sequence, such as 1s, 2s, 2p, and so on. This systematic filling order is essential for predicting how atoms will interact and bond with one another in various chemical reactions.