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200
440 BC -Democritus
He was a Greek philosipher who discovered the atom. -
201
440 B.C. -Aristotle
Aristotle was a Greek philospher who disagreed with the ideas of Democritus by saying that you would never end up with a substance that you could not cut. -
John Dalton
Dalton's theory stated: All substances are made up of atoms. Atoms are small particles that cannot be created, divided, or destroyed. Atoms of the same element are exactly alike, and atoms of different elements are different. Atoms join with other atoms to make new substances. -
J. J. Thomson
Thomson discovered that there are even smaller particles inside of an atom, so atoms can be divided into even smaller parts that he named electrons. -
Ernest Rutherford
Rutherford tested Thomson's theory of the atom by aiming a beam of small, positively charged particles at a thin sheet of gold foil which had a special coating behing the foil which would glow when hit by positivley charged particles. Rutherford expected that the particles to pass right through the sheet, but to his suprise some of the particles bounced right back. -
Ernest Rutherford
Rutherford revisited the idea of the atomic theory and he made a new idea of the atom. He proposed that in the center of an atom is a small, extremly dense, positively charged part called the nucleas. -
Niels Bohr
Bohr studied the way that atoms react to light. Bohr's results led him to propose that electrons move around the nucleus in certain paths, or energy levels. In his model there are no paths between the levels. But electrons can jump the levels as rungs on a ladder. -
Erwin Schrodinger and Werner Heisenburg
Schrodinger and Heisenburg both contributed to the modern atomic theory by further explaning the nature of atoms and that they do not travel in paths, but in regions called electron clouds.
