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460 BCE
Democritus
In the tradition of the atomists, Democritus was a thoroughgoing materialists who viewed the world in terms of natural laws and causes. This differentiated him from other Greek philosophers like Plato and Aristotle, for whom philosophy was more teleological in nature – i.e. more concerned with the purpose of events rather than the causes, as well things like essence, the soul, and final causes. -
John Dalton
He calculated atomic weights from percentage compositions of compounds, using an arbitrary system to find the likely atomic structure of each compound. If there are two elements that can combine, their combinations will happen in a certain order. The first compound will have one atom of A and one of B; the next, one atom of A and two atoms of B; the next, two atoms of A and one of B; and so on. Hence, water is HO. -
Ernest Rutherford
Frederick Soddy arrived at McGill in 1900 from Oxford, and he collaborated with Rutherford in creating the “disintegration theory” of radioactivity which regards radioactive phenomena as atomic processes. The theory was supported by a large amount of experimental evidence, a number of new radioactive substances were discovered and their position in the series of transformations was fixed. -
J.J. Thomson
Thomson determined that all matter is made up of tiny particles that are much smaller than atoms. He originally called these particles 'corpuscles,' although they are now called electrons. This discovery upended the prevailing theory that the atom was the smallest fundamental unit. -
niels bohr
Bohr received the 1922 Nobel Prize in Physics for his work on atomic structures, and he would continue to come up with revolutionary theories. He worked with werner Heisenberg and other scientists on a new quantum mechanics principle connected to Bohr's concept of complementarity . The concept asserted that physical properties on an atomic level would be viewed differently depending on experimental parameters, hence explaining why light could be seen as both a particle and a wave, never both. -
James Chadwhick
In 1932, Chadwick made a fundamental discovery in the domain of nuclear science, he proved that electrons are real. In contrast with the helium nuclei which are charged this new tool in atomic disintegration need not overcome any electric barrier and is capable of penetrating and splitting the nuclei of even the heaviest elements. Chadwick in this way prepared the way towards the fission of uranium 235 and towards the creation of the atomic bomb.
