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405
Democritus (BC)
Created idea of existence of atoms, belived they were indivisible and indestructible. He lacked scientific exprimental proof. -
Dalton's atomic theory
Expirimented to prove Democritus's belifes on atoms, created Dalton's atomic theory, which says that all elements are composed of indivisible atoms, that are identical within the same element, and atoms can participate in both chemical and physical reactions. Chemical reactions dont change what element the atoms are. -
Goldstein discovers proton
Made cathode ray tube, realized that there were (positively charged) particles moving in the opposite direction of the electrons, towards the negative charge. -
J.J. Thomson Discovers Electron
Using a voltage source and 2 metal disks, one positive, one negatively charged, called annode and cathode respectively, Thompson realized that in between there was a beam of light (cathode ray) moving in the direction of th positively charged plate. He concluded that there must be a group of negatively charged particles inside an atom, because negative charges attract. -
Curies discover "radioactivity"
By expirimenting with pitchblende, and ore of uranium, radium and polonium, they discover that the conductivity was 300 times stronger than the uranium itself. Using the newly discovered chemical properties of these elements, they coined the term, and discovered the property of, radioactivity. -
Hantaro Nagoka suggest nucleus
Suggests the idea of nuclei, and electrons move like saturns rings. -
Rutherfords gold foil expiriment
Shot alpha particles at gold foil, most went through unaltered, but some deflected greatly or bounced back. He concluted that those ones hit a small, dense, positive charged area called "the neclus". Therefore, most of an atom is empty space. -
Bohr electron Model
Bohr suggested that electrons had specific orbits around the nucleus, with fixed distance from the nucleus, and energy levels. -
Millikan Oil drop expirement
Used to discover size of electron (1.60*10^-19 culombs) by suspending an drop of oil in the air using electro-magnetic charges -
Luis de Broglie
Propsed the idea of electrons as waves. -
Erwin Schrodinger
After creating mathematical formulae on the motion of electrons, he realized that electrons do not orbit in rings, but in "probablility clouds". -
Chadwick discovers neutron
Realize there was another particle in nucleus, by realizing that atomic numbers did not line up with atomic masses.
(source: http://www.pbs.org/wgbh/aso/databank/entries/dp32ne.html)
