who discovered the nucleus?
Ernest Rutherford
Atomic theory
 Ernest Rutherford
who came up with the theory of continuous matter Pre-Socratic Greek philosophers Leucippus and his pupil Democritus what is atomic theory? It is the scientific theory that matter is composed of particles called atoms.
wiki:1586448
Atomic theory [SEP] Discovery of the nucleus
Thomson's plum pudding model was disproved in 1909 by one of his former students, Ernest Rutherford, who discovered that most of the mass and positive charge of an atom is concentrated in a very small fraction of its volume, which he assumed to be at the very center. Ernest Rutherford and his colleagues Hans Geiger and Ernest Marsden came to have doubts about the Thomson model after they encountered difficulties when they tried to build an instrument to measure the charge-to-mass ratio of alpha particles (these are positively-charged particles emitted by certain radioactive substances such as radium). The alpha particles were being scattered by the air in the detection chamber, which made the measurements unreliable.