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https://courses.lumenlearning.com/cheminter/chapter/daltons-atomic-theory/#:~:text=Summary,extremely%20small%20particles%20called%20atoms.
John Dalton experimented a lot with gasses, and eventually branched out into the other states of matter, and concluded that there are atoms with atomic weights, and later created the very first atomic weight chart, previous to this, the atoms had no experimental backbone, and thus were considered fake -
https://www.sciencehistory.org/historical-profile/joseph-john-j-j-thomson#:~:text=In%201897%20Thomson%20discovered%20the,invention%20of%20the%20mass%20spectrograph.
JJ Thomson experimented with rays against electrically charged plates and found that there were particles much smaller than atoms, and found that these particles (electrons) played a significant role in the charge of atoms -
https://www.nobelprize.org/prizes/chemistry/1908/rutherford/biographical/
Rutherford threw alpha particles over very thin gold, and the alpha particles bounced in every direction, meaning that the atoms were more separated in organized layers, were positively charged, and are very dense, as opposed to the previously theorized Plumb-pudding model -
https://www.nobelprize.org/prizes/physics/1922/bohr/facts/
Bohr benefited off of previous quantum experiments, specifically JJ Thomson and Rutherford's experiments to propose the activity of electrons, and radioactivity, adding more detail to the electrons of the outskirts of atoms -
https://www.nobelprize.org/prizes/physics/1933/schrodinger/facts/
Erwin was able to make an equation that stated that electrons could absorb certain wavelengths, further contributing to the behavior of atoms. -
https://www.nobelprize.org/prizes/physics/1935/chadwick/biographical/
Chadwick, by bombarding Beryllium with alpha particles, was able to prove the existence of neutrons, particles with no charge, the last particle in an atom