Energy required to separate a particle from a system of particles or to disperse all the particles of a system. Nuclear binding energy is the energy required to separate an atomic nucleus into its constituent protons and neutrons. It is also the energy that would be released by combining individual protons and neutrons into a single nucleus. Electron binding energy, or ionization potential, is the energy required to remove an electron from an atom, molecule, or ion, and also the energy released when an electron joins an atom, molecule, or ion. The binding energy of a single proton or neutron in a nucleus is about a million times greater than that of a single electron in an atom.