The discoveries made by J.J. Thomson and Ernest Rutherford caused the modification of John Dalton's atomic model in several ways:
Thomson's discovery of the electron: Thomson discovered the electron, a negatively charged particle, in 1897, and proposed the "plum pudding" model of the atom. This model showed the atom as a mass of positive charge with electrons randomly scattered throughout it. This discovery challenged Dalton's idea of the atom as an indivisible particle.
Rutherford's gold foil experiment: In 1911, Rutherford conducted the gold foil experiment, in which he bombarded a thin sheet of gold with alpha particles. He found that most of the particles went straight through the foil, but some were deflected at large angles, suggesting that the positive charge in the atom was concentrated in a small central region. This led to the development of Rutherford's atomic model, in which the nucleus of the atom contains most of the positive charge and is surrounded by electrons in orbit.
These discoveries showed that the atom was not as simple as Dalton had thought, and led to the development of more sophisticated models that better explained the structure and behavior of atoms