The binding energy that holds nuclei together “shows up” as
“missing” mass.
Deuterium is an isotope of hydrogen which contains a
neutron, a proton, and an “orbiting” electron.
mass of hydrogen
1.0078 u
mass of neutron 1.0087 u
sum 2.0165 u
mass of deuterium
2.0141 u
difference 0.0024
u
Since 1 u of mass has an energy equivalent of 931 MeV, the
missing mass is equal to 931x0.0024 MeV = 2.2 MeV.
The fact that this mass deficit is the binding energy is
demonstrated by experiments which show that it takes 2.2 MeV of energy to split
a deuterium into a neutron and a proton.
Nuclear binding energies range from 2.2 MeV for deuterium to
1640 MeV for bismuth-209.
These binding energies are enormous; millions of times
greater than even the energies given off in highly energetic chemical
reactions.
We usually talk in terms of binding energy per nucleon,
which is 2.2/2=1.1 MeV per nucleon for deuterium, or 1640/209=7.8 MeV per
nucleon for bismuth-209.
The figure below shows a plot of binding energy per nucleon
as a function of mass number.