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Democritus
Democritus was a Greek philosopher who originally came up with the idea of an atom. His concept of the atom was primitive and Aristotle turned down the idea, so many other people disproved of it, too. -
John Dalton
Dalton made some revisions to Democritus's original model. He said atoms make everything and they can't be created, divided, or destroyed. He also said atoms of the same element are alike and the atoms of different elements are different, and atoms can conjoin with different atoms to make new elements. -
Thompson
Using a cathode-tube ray, J. J. discovered that a positive plate would attract an invisible beam. He concluded that the beam has partices with a negative charge that are today known as electrons. -
Rutherford
In Ernest Rutherford's experiment, he aimed positively charged particles at a gold sheet of foil. The majority of the particles passed through, however some were slightly deflected or even bounced back. This is when the idea of a nucleus came into play. -
Bohr
Niels Bohr came up with the idea that electrons travel around the nucleus in definite paths. He explained that there are levels that are a certain distance away from the nucleus, but electrons can jump from one level to another. This model could predict some atomic behavior, however it still needed to be worked on. -
Modern Theory
The Modern Theory is what we know today about electrons. For example, we know that electrons don't move in definite paths as Bohr suggested. The path of a moving electron can't be predicted, however there are things in atoms called electron clouds that we use to predict where the electrons are most likely located.
