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Greek philosopher, Democritus posed the question: "If you break a piece of matter in half, and then break it in half again, how many breaks will you have to make before you can break it no further?' Democritus believed that it had to end at some point. He called these basic matter particles 'atoms'
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It was not until the 1800s that scientists began to question the structure of atoms again. An english chemist, John Dalton performed experiments proving that various chemicles contained elementary particles named atoms. Although he had not yet discovered their structure he had proved something fundemental in their understanding
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Dmitri Mendeleev attempted to classify each element by an exact principle. The only unchanging data that was available was the atomic weight of elements. He was able to create a table and therefore determine that several, unidentified elements should exist. This lead to the discovery of scandium, gallium and germanium.
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Henri Becquerel was using naturaly fluorescent minerals to study the properties of x-rays. He proved that uranium emitted radiation without an external source such as the sun and thus he had discovered radioactivity.
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A the time, physicists thought that light consisted of waves but it was Albert Einstein who discovered that the energy behaved like discrete particles. He called this 'Photons'
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Niels Bohr developed the theory that certain properties only occur in discrete amounts (Quanta)
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In 1919, Ernest Rutherford finally identified the particles of the nucleus as positvely charged matter and discovered protons.
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J.J Thompson discovered the existence of electrons and introduced a model for the structure of the atom. He also found that electrons are negatively charged particles and therefore deduced that matter must have a positive charge.
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The discovery of a new elementary particle was made
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String Theory was first formulated when Gabriele Veneziano described the strong interaction of particles.
