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In the 5th cent. B.C. the Greek philosophers Democritus and Leucippus proposed that matter was made up of tiny, indivisible particles they called atom, or in Greek "a-tomos".
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1) Chemical elements are made of atoms.
2) The atoms of an element are identical in their masses
3) Atoms of different elements have different masses
4) Atoms only combine in small, whole number ratios such as 1:1, 1:2, 2:3 and so on.
5) Atoms can be neither created nor destroyed -
J.J. Thomson discovered that the atom was not solid, but made of many different smaller pieces.
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Ernest discoverd that part of the atom was contained within the nucleus and most of the atom was indeed empty space.
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Electrons are not particles, they are actually waves.
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The negitivly charged electron orbits the positivly charged nucleus.
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Discovered the neutron.
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Heinsberg worked out that particles had a lot more energy over short distances than expected. He realized that a particle can borrow energy as long as it is paid back in a short time.
