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450
Aristotle (332 B.C.)
<ahref='http://www.angelfire.com/sc2/atomtheory/atistotle_atom.jpg' >Aristotle's Atomic Model</a>
Approximate date. Aristotle did not believe that everything was made up of atoms, so he thought that the atomic idea was useless. He believed that the Greek theory of atoms being of different sizes, regular geometric shapes and being in constant motion. He developed the theory that all matter consisted of four elements: Earth, Air, Water and Fire. -
450
Democritus (492 B.C)
Democritus Atom Model
This was the approximate date that Democritus discovered the atom. He made the claim that "Everything is made up of atoms." He also made the statement that, "The more any indivisible exceeds, the heavier it is." He discovered that the atom made up matter and that the actual atom was a spherical shape. -
Dalton
Dalton's Atomic ModelApproximate date. Proposed an "atomic theory" with spherical solid atoms based on the measurable properties of mass. Dalton stated that, "The reason an element is pure is because all atoms of an element were identical and that in particular they had the same mass."(1805) His atomic model was similar to the one created by Democritus. -
Thomson
Thomson's Atomic Model
Approximate date. Thomson suggested that, "A model of the atom as a sphere of positive matter in which electrons are positioned by electrostatic forces." (1904) Thomson's most important experimental program focused on determining the nature of positively charged particles. He proposed the "Plum Pudding" model because of his cathode ray experiment that proved the existence of electrons. -
Bohr
Bohr's Atomic Model
Approximate date. Bohr stated that, "The electrons moved around the nucleus in large orbits." (1913) -
Rutherford
Rutherford's Atomic Model
Rutherford described his atomic theory as the atom having a central positive nucleus surrounded by negative electrons.He stated that, "The energy produced by the breaking down of the atom is a very poor kind of thing. Anyone who expects a source of power from the transformation of these atoms is talking moonshine."(1933). His atomic model consisted of
