Democritus came up with a theory postulated on the idea that the world is made up tiny little pieces of matter called atoms. He believed they were tiny pieces of uncuttable matter moving through space.
John Dalton discovered many things in the atomic field. One of the things he is very known for is his discovered of how atoms can neither created nor destroyed. he also suggested that we give elements symbols.
Thomson discovered that there were negatively charged particles. he proposed that these particles' positions were based on electrostatic forces.
Ernest Rutherford discovered a positively charged part of an atom called the nucleus. He said that atoms are mainly empty spaces and of the few electrons, move randomly.
Bohr gave the answer to the problem Rutherford's model posed. He said that electrons acted like waves and particles. Which meant that the atomic scale did not act the same as our Laws of Physics did.
Schrodinger was an Austrian physicist who proposed the quantum mechanics of an atom. He used equations to predict the location of an electron in an atom.