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Dalton experimented that the total pressure of a mixture of gases accounted for the sum of each individual gas before mixed
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Thomson experimented with cathode rods to show that all atoms contain small negative charged subatomic particles known as "Electrons". He's also famous for the "plum pudding" model (Blueberry Muffin).
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Rutherford shot alpha particles into gold foil. He noticed that the particles would go straight through, change path, or bounce back. By doing this he inferred that atoms or mostly empty space, nucleus is small with a positive charge, and that the nucleus is small and dense
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By studying the orbit motion of a atom. Bohr and his mentor, Rutherford, they realized that electrons lose energy and collapse into the nucleus. Bohr proved that electrons can orbit the nucleus as long as they're a certain distance.
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Chadwick discovered the neutron in atoms. With this, he also figured out that they don't have a charge but contribute to the atomic weight just like a proton. With isotopes, his discovery of the Neutron helped. He found out that isotopes (same element) have the same amount of protons and electrons but differ in the amount of neutrons in the nucleus.
