Summary:
- The Aufbau principle states that an electron occupies orbitals in order from lowest energy to highest.
- Figure below shows the order of increasing energy of the sublevels.
- Principal energy levels are color coded, while sublevels are grouped together and each circle represents an orbital capable of holding two electrons.
- The lowest energy sublevel is always the 1s sublevel, which consists of one orbital.
- The single electron of the hydrogen atom will occupy the 1S orbital when the atom is in its ground state.