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Newton
Newton put forward a mechanical universe with small solid masses in motion. -
Dalton
Dalton proposed an "atomic theory" with spherical solid atoms according to measurable properties of mass. -
G.J Stoney
Stoney proposed that electricity was made of separate negative particles he called "electrons". -
J.J Thomson
The scientist discovered that the atom was not an ‘indivisible’ particle but just like a jigsaw puzzle made of smaller pieces. He explained why a stream of glowing material could be seen when an electric current was passed through a vacuum tube. Thomson stated that electrons are basically small atoms carry negative charges. -
Planck
Planck used the idea of quanta (separate units of energy) to explain hot glowing matter. -
Nagaoka
Nagaoka postulated a "Saturnian" model of the atom with flat rings of electrons spinning around a positively charged particle. -
Millikan
Millikan constructed an oil drop experiment, determining the charge (e=1.602 x 10 -19 coulomb) and the mass (m = 9.11 x 10 -28 gram) of an electron. Milikan determined the speed of light and the charge of electrons. -
E. Rutherford
Using alpha particles as atomic bullets, probed the atoms in a piece of thin (0.00006 cm) gold foil . He established that the nucleus was: very dense, very small and positively charged. He also assumed that the electrons were located outside the nucleus He also explains why the electrons spin around the nucleus. . -
H.G.J Mosely
Using x-ray tubes, determined the charges on the nuclei of most atoms. He wrote "The atomic number of an element is equal to the number of protons in the nucleus". This work was used to reorganize the periodic table based upon atomic number instead of atomic mass.Mosely justfied many concepts in chemistry. -
Bohr
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.He believed that electrons travel only larger orbits and he explained that the outer orbits could hold more electrons than the inner ones. -
James Chadwick
Using alpha particles and discovered a neutral atomic particle with a mass close to a proton. This was the discovery of the neutron.
