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John Dalton 1776-1844
Dalton came up with 5 principles about the atom, they are:
1.) all matter is made up of indivisble and indestructible particels called atoms.2.) Atoms can't be created, divided or destroyed in reactions. 3.) Atoms of a given element are identical. Atoms of diferent elements have different masses and properties. 4.) Atoms combine in simple, whole number ratios to form compounds. 5.) In chemical reactions atoms are combined, seperated or rearranged. -
J.J. Thomson 1856-1940
Thomson conducted the Cathode Ray tube experiment, during the experiment he found that there is something negatively charged in atoms. He realized the negative charge was in all atoms and that there has to be a positive charge. He announced the rays were electrons and they had negative charges. He proposed the plum pudding model. -
Ernest Rutherford 1871-1937
Rutherford interpreted the gold foil experiment. As a result of the experiment he proposed that all of the positive charge and all of the mass of the atom occupied a small volume at the center of the atom which is the nucleus. Also most of the volume of the atom occupied by the electrons. He also proposed the existence of the neutron. -
Democritus 460-370 B.C.
Was the first to propose the existence of an ultimate particle. He called the particle the atom. He said matter is composed of atoms, which are indivisible. He had no supportive evidence and was rejected because Aristotle has the better reputation. -
Aristotle
Aristotle thought that matter was composed of Fire (hot), water (cold), air (moist), and earth (dry). He also felt that regardless of the number of times you cut a form of matter in half, you will always get a smaller piece. This view was supported for 2000 years due to his reputation. He had no real evidence. -
Period: to
Timeline of Atomic Theory
