Why are all elements with atomic numbers above 82 unstable?

The stability of the atoms of different elements is
dependent on their nuclear binding energy. If the nuclear binding energy of an atom is
more than the repulsive forces between the nucleons, it is stable. It has been seen that
binding energy starts to increase from the atoms of the lightest elements; it
reaches the highest with iron and then begins to drop.

The
nucleus of atoms with a higher binding energy is found to be lighter than the mass of
the constituent nucleons. This decrease in mass is due to energy which is expelled. If
such an atom has to be split an amount of energy equivalent to the decrease in mass has
to be introduced.

In the case of atoms of elements with a
mass greater than 82, the level of binding energy does not allow stability. The force of
repulsion between the particles that constitute the nucleus makes the atoms split and
atoms of new elements are formed as they try to reach a nuclear configuration which is
stable.