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Democritus (400 BC) questioned whether matter could be divided down forever or if there was a limit. He determined there was a limit, which was indivisible, and named it atomos, meaning, "not to be cut."
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John Dalton, theorized that all elements were composed of atoms and atoms of the same element are exactly alike. His research was backed by careful research.
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Thomson (1897) theorized that an atom was not a solid sphere or indivisible, but made up of smaller particles. He thought positive and negative were all mixed together to create a neutral substance. This is referred to as the Plum Pudding Model.
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Ernest Rutherford fired positively-charged particles are a thing sheet of gold foil. Most went through, but some repelled off. HE concluded that a substance is mostly empty space. From this, he theorized that atoms have a central positive nucleus and orbiting negative electrons.
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Published in 1913, Bohr's atomic model is very similar to the planetary model currently in existence. He thought that neutrons and protons made up a nucleus, and electrons are held in orbit around the nucleus by electrical force.
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Erwin Schrodinger developed a mathematical model for the distribution of electrons in an atom. This method does not give the exact location of an electron, but the probability of an electron being in a certain region.
