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Period: 460 BCE to 370 BCE
Democritus
Democritus used his thoughts and thought that if you take an object and keep cutting it, then it will reach a point where it can no longer be cut, which this started the atomic model theory. -
Period: 384 BCE to 322 BCE
Aristotle
Aristotle rejected the ideas of Democritus, instead believing that matter on Earth was made up of four elements – earth, air, fire and water – and the amounts of these elements determined how materials behaved. -
Period: to
John Dalton
Dalton suggested that all elements, which were now arranged in the periodic table, contained atoms, and that atoms of the same element would be identical in size, shape and mass. This theory was called the ‘solid sphere model’ as Dalton believed the atom was a solid sphere. He also stated that compounds were a combination of element -
Period: to
Joseph John Thomson
By studying ‘rays’ within a cathode ray tube, Thomson was able to determine that these ‘rays’ had a mass 1000 times smaller than a hydrogen atom, the lightest piece of matter known to science at the time. He therefore concluded that these ‘rays’ were not rays at all, but very light particles. These particles were also attracted to a positively charged metal plate, indicating that they were likely to be negatively charged. -
Period: to
Ernest Rutherford
Rutherford predicted that if the atom was like Thomson’s plum pudding model, then all the alpha particles should pass straight through the atom undisturbed. This is not what happened! It was true that almost all (99.99%) of the alpha particles passed straight through the foil and were detected at the other side, indicating that the atom was mainly empty space. However, surprisingly, some of the alpha particles bounced back or were deflected as if they had hit something.