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Jan 1, 1000
Democritus - 442 BC
"by convention bitter, by convention sweet, but in reality atoms and void." He proposed that all matter is made up of almost infinate indivisible particles which are different from each other in form, position, and arrangement. -
Period: Jan 1, 1000 to
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John Dalton
English chemist who proposed an "atomic theory" with sperical solid atoms based on measurable properties of mass -
JJ thomson
Thomson used a CRT to determine the charge to mass ratio (e/m) of an electron. he studied "canal rays" and found they were associated with the proton H+.Cathode Ray Tube Experiment -
Thomson
First to measure the electron. Developed the plum-pudding model of the atom. Describes the atom as a slightly positive sphere with small electrons inside. -
Robert Millikan
Millikan used an oil drop expiriment to determine the charge and mass of an electron -
Ernest Rutherford
using alpha particles as atomic bullets, he probed atoms in a piece of gold foil. (gold foil expiriment) he established that the nucleus was very dense, very small, and positively charged.he also assumed that the electrons were located outside the nucleus -
Neils Bohr
A Danish physicist who stated that electrons could only orbit the nucleus in succesively larger orbits around the nucleus. The outer orbits could hold more electrons. The electrons in the outermost shell determine the properties of the atom. -
James Chadwick
by using alpha particles he discovered a neutral atomic particle with a mass close to a proton. the neutron was discovered
