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Democritus
Democritus is a Greek philosopher. He proposed that small particles, atoms, make up all matter. He claimed that they were always moving and that the number of them were infinite. Most thought he was crazy, however, he wasn't. -
John Dalton
Dalton was a British scientist/school teacher. He reintroduced the concept of atoms with evidence. He agreed that all matter is made up of many smaller things called atoms. He also stated that atoms cannot be created, destroyed, or divided. -
J.J. Thompson
This British scientist proved that Dalton's theory had some flaws. He repeated an experiment and discovered that the "indivisible" atom really was divisible. Once separated again he found that there are negatively charged particles, electrons, within an atom. Now he knew that positve charged particles must be there in order to even out with the negative, however he didn't know where they were. So he created what is now called the "Plum in the Pudding" model because the electrons look like plums. -
Earnest Rutherford
As a former student of Thomson's, he began to investigate the atomic theory. After conducting an experiment in which the results were unexplained he changed the theory. He claimed that a positively charged region was in the center of an atom. It would push away other positive particles. Compared to the size of a gold atom, a nucleus is 100,000 times smaller. -
Niels Bohr
This Danish scientist claimed that electrons travel on definite paths around the nucleus. He said that there couldn't be any between the levels, but they're able to jump paths. This was very important information because it became very useful when predicting atomic behavior. -
Modern Atomic Theory
CHANGES: 1.No definite paths for electrons, but rather regions that they're likely to be called Electron Clouds. 2. Neutrons (neutral), protons (+), electrons (-). 3. The number of protons determine atomic number. 4. Isotopes: atoms with different number of neutrons, but different number of protons. 5. Forces that work in an atom: Gravity, electromagnetic force, strong and weak force.
