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400 BCE
Democritus
Democritus lived from 460-370 and made several discoveries about particle Model. He said that atoms are indestructible and if we cut a stone in half and cut that in half...we would reach a point where it would be impossible to divide any more. According to him other than atoms being indestructible, they are also unchangeable and they differ in different matter such as atoms of a plastic and paper will be different, in size shape mass position and arrangement. -
Isaac Newton
Isaac Newton thought that every matter is made of particles but not specifically atoms. The structure of a particle according to him would be in a clustered but ordered structure of matter, commencing with the smallest and most tightly bound clusters, and ending with
the largest and most weakly bound ones. In short, he believed that there were little tiny pieces of mass that were 'swimming' everywhere. -
John Dalton
Disagreeing with Newton's theory Dalton formally stated in 1802 that everything is made up of tiny atoms. An element is made up of identical atoms that had similar mass and the properties(proton, Neutrons, electrons) of an atom determines the way the element behaves. -
Einstein
Einstein proved the existence of atoms in this world mathematically and he proved that these atoms were in continuous, random, ceaseless motion.