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500
ANCIENT GREEKS - Empedocles 450BC
Suggests that all matter was made from combinations of fire, air, water and earth -
500
ANCIENT GREEKS - Democritus 47BC - 40BC
Proposed that if a sample of matter was cut into smaller and smaller pieces, they would eventually become indivisible. He named them atoms -
500
ANCIENT GREEKS - Aristotle 384BC-322BC
Matter is continuous and infinitely divisible. Supported Empedocles theory. Said that you could change one material into another by varying the proportions of earth, air, fire and water. -
Period: 500 to
History of Atomic Theory
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JOHN DALTON
- Proposed that all matter consisted of tiny particles called atoms
- Atoms could not be divided into smaller particles
- Atoms of the same element were alike
- Atoms combined in simple whole number ratios
- Atoms from each element are different and combine to make other substances
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J.J. THOMPSON
- Discovered the electron which proved that atoms were not indivisible
- Proposed that atoms were positively charged spheres with negatively charged particles (electrons) embedded in them (the plum pudding model)
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ERNEST RUTHERFORD
- Proposed a nuclear model for the atom
- Discovered the nucleus by bombarding a thin gold foil with positively charged particles which were reflected off 1 out of every 10000
- The nucleus was where the positively charged atoms were and was where most of the mass was
- The nucleus had electrons orbiting on energy shells however he proposed that they would eventually spiral in toward the nucleus.
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NIELS BOHR
- Modified Rutherford’s model and proposed that the electrons orbit the nucleus on different energy levels
- Proposed that electrons have different amounts of energy which is why they existed at different levels
- Electrons could move energy levels by gaining or losing energy
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JAMES CHADWICK
- Discover the neutrons in the nucleus
- Found that they had no electric charge and the same mass as the proton