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200
440 BC - Democritus
- Democritus came up with the idea of the smallest particle of matter
- Named it an atom which is greek for atomos (undividable)
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201
382 BCE - Aristotle
- thought that you could never end up with the smallest particle
- people thought he was right for a long time, but he was wrong
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1803 - John Dalton
Said atoms were small hard objects.
- said all substances are made of atoms. Atoms are small particles that cannot be created, divided, or destroyed
- Atoms of the same element are exactly the same, and atoms of different elements are different.
- Atoms join with other atoms to make new substances -
1897 - J.J. Thompson
- Discovered there were small particles inside atoms, which meant atoms could be divided.
- used a cathod-ray tube to test his experiment
- he discovered electrons and said they were like plums in pudding. (the atom is the pudding, the electrons are the plums).
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20th Century - Schrodinger and Heisenberg
- Schrodinger was Austrian
- Heisenberg was German
- further explained electrons by showeingthat electrons didn't follow direct paths
- they introduced the idea of "electron clouds" which are regions where electrons are.
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1909 - Ernest Rutherford
- was a former student of Thompsan's
- tested Thompson's theory by firing radium particles at a sheet of gold foil. He checked to see where the particles defected to on a small circular 'wall' that surrounded the foil.
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1911 - Ernest Rutherford
- Discovered that the electrons fly around the nucleus because a positively charged particle would be pushed away from the positive charge of the nucleus.
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1913 - Niels Bohr
- was a Danish scientist who worked with Ruthorford
- said that electrons orbit the nucleus in a certain paths similar to the rungs of a ladder
- he called it energy levels
