Realized that matter is made up of atom. Atoms are so small that they can not be divided.
Formed the atomic theory, which states all matter is composed of indestructible particles called atoms.
He discovered the electron and developed the plum pudding model of the atom.
He used an alpha particle emitter. He used this on a piece of Gold foil. He used to to look at charges. He discovered the nucleus and used his results from the gold foil experiment to state that the atom were in small positive charged balls at the center of the atom.
Stated that electrons moved around the nucleus in large orbits. He also presented the Bohr atomic model which appointed that atoms imbibe or emit radiation only when the electrons abruptly jump between allowed, or stationary, states.
He discovered neutrons using evidence collected by Irene Joliot-Curie. She discovered that beryllium was bombarded with positively charged alpha particles. With this information Chadwick discovered that this beam was not able to bend electric or magnetic fields. Neutrons were found to have the same mass as protons. .