Electron orbitals that have the same energy levels are called degenerate orbitals. When assigning electrons to orbitals in determining electron configurations, the Aufbau principle states that lower energy orbitals are filled before higher energy orbitals. Hund's rule states that degenerate orbitals are filled evenly, not unevenly, before moving to higher energy orbitals. For example, p orbitals consist of three degenerate orbitals that all have exactly the same energy level. We put a single electron in each orbital first, then put a second electron (of opposite spin) in each orbital to fill them with a total of six electrons.