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460
Democritus
460 B.C. Democritus discovered the atom. He asked the question: If you break a piece of matter in half, and then break it in half again, how many breaks will you have to make before you can break it no further? -
Dalton
Theories: 1) all substances are made of atoms. Atoms of the same element are exactly alike. Atoms of different elements are different
2) Atoms are small particles that cannot be created
3) [articles can not be divided, or destroyed
-join with other atoms to make new substances
-published atomic theory in 1803 -
Thomson
Thomson discovered electrons -
Chadwick
proves the existence of the neutron in 1932 what accelerated the research in nuclear physics immensly -
Rutherford
Rutherford tested and improved Thomson's theory
-He stated that not all atoms are soft blobs of matter -
Bohr
Electrons move around nucleus in certain paths
