Democritus of Adbera created the idea of atoms. Democritus had the thought of what if I break a piece of matter in half then in half again till I could not break it in half any more? Democritus called these atoms. Democritus then came up with the thought that between atoms there is empty space.
Aristotle did not like the idea of the atom. Aristotle 's idea of atomic model was no smallest part of matter and that different substances were made up of proportions of fire, air, earth, water, and aether. But Aristotle did not have any test to prove his idea.
John Dalton did a experiment with 6 different gasses, various chemicals at different temperatures, both in a vacuum and in air. this showed to consist of lumpy particles called atoms. Dalton did not figure out there structure but did know what he discover pointed to something fundamental.
John Dalton's diagram is here
Joseph John Thomson discovered the electron and proposed a model for the structure of the atom(lump of pudding.) Thomson also knew that electrons had a negative charge and thought that matter must have a positive charge.
Max Planck worked with Einstein they both came up with the theory said "light would be thrown back not by decades." But they discovered the anomalous behavior of specific heat at low temperatures as another example of a phenomenon.
Max Planck diagram is here
Robert Millikan worked on the oil-drop experiment that measured the charge on a single electron. He discovered that integer multiples of a common value are 1.592 × 10−19 coulomb.
Ernest Rutherford used the gold foil experiment and thought that electrons must exist somewhere within this empty space. Also thought negative electrons orbited a positive center in a manner like the solar system where the planets orbit the sun. But not till 8 years later he identify the particles of the nucleus as discrete positive charges of matter.
Niels Bohr thought that if electrons travel in orbits around the atom's nucleus. He believed that the chemical properties of each element being largely determined by the number of electrons in the outer orbits of its atoms. Also Bohr thought
that electron could drop from a higher-energy orbit to a lower one creating a photon this was that bases of Bohr theory.
Niels Bohr diagram is here
Louis de Broglie add to Bohr's model. Broglie said that a wavelength associated with an electron and derived from its momentum yields a standing-wave pattern.
Erwin Schrödinger had an idea "Why not go all the way with particle waves and try to form a model of the atom on that basis?" But Schrödinger did not question the waves so he gave them a symbol.
Werner Heisenberg theory say a proton shoots a photon at the electron. Then the electron shoots a photon back at the proton.
James Chadwick discovered neutrons do not need to overcome any Coulomb barrier. So neutrons can enter nuclei of each the heaviest elements. Chadwick also won a Nobel Prize in Physics in 1935 for discovering about neutrons.