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Around 440 BC, Democritus discovered atoms, or "atomos" by breaking up material into his pistol.
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John Dalton, a British scientist, refined Democritus' theory. He found that atoms of the same element are exactly alike, and ones of different elements are different.
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J.J. Thomson found that there are even smaller particles inside of an atom, what we now call electrons.
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After two years of discovery, in 1911 Rutherford concluded that atoms are mostly empty space. He also said that there was a tiny spot of dense matter - a nucleus.
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In 1913, Niels Bohr came up with what is very close to our current understanding of atoms. He said that the electrons were in orbit around the nucleus.
