ANSWER
Step-by-step explanation
An atom is defined as the smallest indivisible particle of an element that can take part in a chemical reaction and still retain its properties.
There are three sub-atomic particles which are; electron, proton, and neutron.
J.J Thomson contributed to the development of the atomic theory when it performed an experiment on cathode ray tubes.
The experiment shows that all atoms contain tiny negatively charged called electron. This led to the discovery of electron
Rutherford contributed to the development of the atomic theory when he discovered that the atom is mostly empty space, nearly all the mass of the atom is concentrated in a tiny central nucleus. He also found out that the nucleus is positively charged and this led to the discovery of proton
Niels Bohr contributed to the development of the atomic theory when he proposed a model of the atom in which the electron was able to occupy only certain orbit around the nucleus. This model was the first to use quantum theory.
Schrondinger contributed to the development of the atomic theory when he assumed that matter can behave as both particles and waves.