Many different orbitals exist in an atom. An orbital is a region where a given electron (or pair of electrons) is most likely to exist. But the orbital to which a given electron is assigned is not just random. Electrons enter orbitals in a predictable manner that obeys certain rules. The three rules are shown in the table below.
| Aufbau principle | Electrons will always fill the lowest energy orbitals first. |
|---|---|
| Hund's rule | When there are multiple orbitals with the same energy, every orbital must have one electron before any orbital will get a second. |
| Pauli exclusion principle | No two electrons in an atom can have identical quantum numbers. |
Question
How do electrons enter orbitals within an atom?
Electrons enter orbitals in a predictable way that follows specific rules, rather than being assigned randomly.
