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BC 500: Democritis said that all matter is made up of atoms.
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BC 384-322: Aristotle said that there are four elements: Earth, Air, Fire, and Water.
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Lenard proposed the model of an atom to have each positive and negative charge bound together. He also did a large amout of work with cathode rays.
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Thompson introduced the plum pudding model of an atom. He said that the space in it was positive and that electrons floated around inside it.
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Albert Einstein said that mass equals the speed of light squared.
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R.A. Millikan found the mass and charge of an electron using his oil drop experiment. Mass=9.11 x 10 -28 gram Charge: 1.602 x 10 -19 coulomb
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After doing his gold foil experiment, Rutherford developed his atomic theory. He said that the nucleus is positively charged and in the middle of the atom. He proposed that the rest of the atom is empty and electrons orbit around it.
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Bohr proposed the model of an atom where elecrons move like planets around a nucleus. He added that they have different energy levels and can jump from one to another when they are excited and when they absorb or emmit photons.
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Rutherford discovered the proton by doing many experiments around radiation. He was able to isolate it to find that it was positively charged.
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Shroedinger and Heisenberg decided that it is uncertain where an electron actually is inside an atom.
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Cockcroft and Walton discovered alpha particles by building a linear accelerator and attacking lithium with protons.
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James Chadwick discovered the neutron. An atomic particle with the same mass as a proton.
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Enrico Fermi made the first chain reaction releasing energy from the atom's nucleus.
