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Period: 460 BCE to 370 BCE
Democritus
Democritus was the first philosopher to theorise about the atom. In the year 442 BCE, he hypothesised that if you take an object and cut it into smaller and smaller pieces, eventually you would reach a point where you could no longer cut it anymore. You would end up with a piece that was indivisible. Democritus called this piece atomos, which means ‘indivisible’ in Greek. -
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. Aristotle had such an influence over people at the time that it took about 2000 years for Democritus’s theory to be re-examined. -
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John Dalton
Dalton is credited for initiating research into modern atomic theory in 1803, more than 2000 years after Democritus first proposed his ideas on the atom. 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. -
Period: to
Joseph John Thomson
Thomson was the first scientist to discover particles smaller than the atom, disproving Dalton’s and Democritus’s theories. Surprisingly, the first subatomic particle to be discovered was the lightest – the electron – and Thomson won a Nobel Prize for his work in 1906. 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 -
Period: to
Ernest Rutherford
In 1911, Ernest Rutherford and colleagues Hans Geiger and Ernest Marsden fired alpha particles (helium nuclei) at a thin piece of gold foil, in the famous gold foil experiment.