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Democritus was a central figure in the development of the atomic theory of the universe. He theorized that all material bodies are made up of indivisibly small “atoms.” -
Dalton showed that common substances always broke down into the same elements in the same proportions. -
Dmitri Mendeleev jotted down the symbols for the chemical elements, putting them in order according to their atomic weights and inventing the periodic table. While doing so he discovered patterns and trends in the periodic table. -
JJ Thompson is credited for the discovery of the electron. He showed atoms as uniformly packed spheres of positive matter filled with negatively charged electrons -
He discovered alpha and beta rays, set forth the laws of radioactive decay, and identified alpha particles as helium nuclei. He is also credited with the finding of the proton -
Bohr discovered that electrons travel in separate orbits around the nucleus and that the number of electrons in the outer orbit determines the properties of an element. -
Werner Heisenberg is credited with the development of the uncertainty principle (a particle's position, energy and speed can never be precisely known) -
James Chadwick is known for his discovery of the neutron, or the "missing mass" that scientists were trying to discover. He was also part of the development of the first atomic bomb program commissioned by the US government in 1940.
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