A diagram in which the labels for atomic orbitals are shown within shaded circles. These are linked by a twisting arrow, indicating progressively increasing energy. The lowest energy orbital is the 1s, followed by: 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p and finally 8s.