The Development of the Atom By floreyx3 Jan 1, 1704 Democritus' Theory Democritus proposed that there was a limit to how much matter could be subdivided and that there existed an ultimate, indivisible particle called an atom. No experiments were done at this stage. Jan 1, 1704 Newtown's Theory Isaac Newton proposed a mechanical universe with small solid masses in motion. He also produced the three laws of motion. Jan 1, 1803 Dalton's discovery Dalton did many experiments and found that elements always combined in fixed ratios. He also proposed an "atomic theory" with spherical solid atoms based upon measurable properties of mass. Jan 1, 1894 G.J Stoney's Theory G.J. Stoney proposed that electricity was made of discrete negative particles he called electrons. Jan 1, 1897 J.J. Thomson's experiments Thomson and other scientists all experimented with passing electricity through gases at low pressures in sealed glass tubes, Jan 1, 1900 Plank's explanation Max Planck used the idea of quanta (discrete units of energy) to explain hot glowing matter. Jan 1, 1903 Nagaoka's theory Nagaoka postulated a "Saturnian" model of the atom with flat rings of electrons revolving around a positively charged particle. Jan 1, 1909 Milikan's experiment Milikan's oil drop experiment determined the charge and mass of an electron. Jan 1, 1911 E. Rutherford's Theory He established that the nucleus was: very dense, very small and positively charged. He also assumed that the electrons were located outside the nucleus. Jan 1, 1914 H.G.J Mosely's theory He wrote “The atomic number of an element is equal to the number of protons in the nucleus". Jan 1, 1932 James Chadwick's experiment The neutron was discovered. Jan 1, 2010 Bohr's discovery Developed an explanation of atomic structure that underlies regularities of the periodic table of elements. His atomic model had atoms built up of successive orbital shells of electrons.