A diagram showing how the energy levels of a transition-metal atom split when it is placed in a ligand field. The vertical axis shows the energy and the horizontal axis shows the strength of the ligand field, with zero ligand field strength at the centre of the horizontal axis. That the splitting for d n is the same as d n+5 and the opposite of d10−n is readily seen on an Orgel diagram, both for octahedral and tetrahedral fields. The spectroscopic, optical, and magnetic properties of complexes of transition metals are made clear in such diagrams. Orgel diagrams are named after Leslie Orgel, who developed them in 1955.