ATOM PRIOR TO 1900 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". The reason why they assumed this is because nothing can come from nothing. Democritus believed that all atoms were firm and solid, but they could not all be the same. If all atoms were identical, there would be no satisfactory explanation of how …showed first 75 words of 424 total…

…showed last 75 words of 424 total…classify all of the atoms, both natural and man made, by their atomic number (that is to say the number of protons that they contain). Then in 1897, Thompson discovered the first component part of the atom: the electron, a particle with a negative electric charge. In 1904, he proposed an initial model of an atom, since nicknamed "Thompsons pudding". He imagined the atom as a sphere full of an electrically positive substance mixed with negative electron.