John Dalton was the first to 'propose' the atomic model of an element. But he said it was indivisible
In the 5th cent. B.C. the Greek philosophers Democritus and Leucippus proposed that matter was made up of tiny, indivisible particles they called atom, or in Greek "a-tomos". The reason why they assumed this is because nothing can come from nothing. Around 1803, John Dalton (1766-1844) developed the first useful atomic theory of matter. He imagined the atom as a sphere full of an electrically positive substance mixed with negative electron. Then in 1897, Thompson discovered the first component part of the atom: the electron, a particle with a negative electric charge.
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