Atomic energy is the energy that binds the atomic particles like protons, neutrons and electrons all together in one atom.
energy is mainly the energy of attraction in the nucleus. When two
nuclei are merged together into one nucleus by FUSION , then a lot of
atomic energy is released.
When a nucleus of a heavy atom is
bombarded with some protons and neutrons at high speeds, the nucleus
breaks into two smaller nuclei. This process called FISSION releases a
lot of atomic energy.
Atomic weight is the mass of the nucleus,
which is the sum of number of protons multiplied by the mass of protons
and the number of neutrons multiplied by the mass of neutrons.
Atomic energy is more in the heavier atoms. When heavier (more atomic weight) atoms are broken, there is more energy.
Atomic weight of the nuclear material changes when atomic energy is
released. In fact the material gets converted into material of smaller
atomic weight, when fission happens.