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400
Democritus
Everything is composed of atoms, which are physically, but not geometrically; indivisible. Atoms are instructable, in motion, and infinite number of atoms -
Period: 400 to
Atom TImeline
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John Dalton
Atomic Theory: matter is made up of atoms that are indivisible and indestructible. -
James Chadwick
Used a method for tracking particle radiation and knocked the protons out of the nucleus. The nucleus still had mass, finding that neutrons exists. -
J.J. Thomson
discovered electrons by experimenting with cathode ray. cathode rays were negatively charged. studied positively charged particles in neon gas.
proposed plum pudding model -
Robert Milliken
Oil Drop Experiment: determined size of the charge on an electron. Determined there was a smallest unit charge or a charge that is quantized. -
Ernest Rutherford
overturned Thomson's model. Gold foil experiment: demonstrated that the atom has a tiny, heavy nucleus. -
Neils Bohr
Quantum Theory: energy is transferred only in certain well defined quantum. Electrons should only move around the nucleus in a prescribed orbit.