Albert Einstien
an atom
They were discovered because the amount of energy they emit was measurable, but the method and manner in which it is emitted was inexplicable at the time.
When energy is absorbed by an atom, the electrons in the atom can jump to higher energy levels. When they return to their original positions, they release the extra energy in the form of light. This is how light is produced in an atom.
light
chadwick discovered neutral atom
When an atom releases energy in the form of visible wavelengths of light, it indicates that an electron in that atom has gone from an excited energy level, back down to a lower energy level.
The structure of the atom was discovered by Ernest Rutherford and Niels Bohr. Rutherford's gold foil experiment led to the discovery of the nucleus, while Bohr proposed the planetary model of the atom with electrons orbiting the nucleus in specific energy levels.
Nuclear fission
When an atom absorbs energy from passing electrons, the electrons may move to higher energy levels within the atom. This can lead to the atom becoming excited or even ionized. Eventually, the atom will release the stored energy in the form of light or heat to return to a more stable state.
Breaking an atom does release energy in a process called nuclear fission, where the nucleus splits into smaller parts. This energy release is a fundamental principle behind nuclear power plants and nuclear weapons.
The nuclear atom was discovered by Ernest Rutherford. He did it with a gold foil experiment.
Nuclear energy is the energy resource that is based on fission, where the nucleus of an atom is split to release energy.