This scatter plot maps all elements by their proton count versus neutron count. The diagonal line shows where N equals Z, representing equal numbers of both particles.

Light elements are most stable when they have roughly equal protons and neutrons. However, as atomic number increases, stable nuclei require progressively more neutrons to compensate for growing electrostatic repulsion between protons. The chart reveals why elements beyond lead (Z=82) have no stable isotopes and why uranium undergoes fission.