The binding energy per nucleon is the energy required to separate all the nucleons in a nucleus from each other. It is a measure of the strength of the nuclear force that holds the nucleus together.

The binding energy per nucleon increases with increasing atomic number up to iron-56. This is because the nuclear force is stronger than the electrostatic force of repulsion between protons up to this point. After iron-56, the electrostatic force becomes stronger than the nuclear force and the binding energy per nucleon decreases.

Therefore, atoms with the greatest mass do not have the greatest binding energies.