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Democritus, a Greek philosopher, and his teacher originated the thought that all matter is composed of indivisible elements.
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John Dalton, developed a theory that matter is simply composed of atoms. He also proposed that these atoms are spherical, and are in motion.
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Pierre and Marie Curie theorized that radioactive particles cause atoms to break down, then releasing radiation that takes the form of energy and subatomic particles.
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JJ Thomson discovers the electron, using properties of cathode rays.
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Ernest Rutherford (known as the father of nuclear physics), developed the theory for the structure of the atom. He used a gold foil experiment, observing the scattering of alpha particles, and demonstrated for the first time the existence of the atomic nucleus.
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Neils Bohr developed the Bohr atomic model, with electrons travelling in orbits around the nucleus, and chemical properties being determined by how many electrons are in the outer orbits.
