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Model representations are used in science to give us an idea of what something looks like, but they aren't the real thing. After discovering electrons, protons, and the neutrality of atoms, scientists began making atomic models to accurately and simply depict what they thought an atom looked like.
J.J. Thomson's "plum pudding" atomic model
Sir J.J. Thomson, who discovered the electron, developed his "plum pudding" model in 1904, named after its resemblance to an English dessert.
Note: In case you are not familiar with plum pudding (figure below to the left), you can think about the model as a watermelon (figure below to the right) instead!
In Thomson's model, the electrons were stuck into a thick soup of positive charge, like the seeds in a watermelon. Can electrons move in Thomson's model? How did the negative and positive charges interact, according to Thomson?
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However, five years later, New Zealander Ernest Rutherford developed a new atomic model after his gold foil experiment.
In this experiment, Rutherford and his coworkers bombarded thin sheets of gold foil with fast moving alpha particles, or positively charged radioactive particles. What did the scientists observe? How did the scientists' predictions compare to their observations?
When forming his model, Rutherford reasoned that most of the atom was empty space. He also believed that the positive charge was concentrated in a small space inside the atom, which he called the nucleus. What observations from his experiment led him to draw these conclusions? How do we define a nucleus today?
Rutherford's model is now known as the nuclear model. What aspect of the atom did this model not address?
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After electrons and protons were discovered, scientists developed atomic models, like the Bohr model and Rutherford's nuclear model, which helped form a clearer picture of atoms. Where are electrons located in an atom? What about protons and neutrons?
However, one problem still existed: why do the large number of positively charged protons in the nucleus not push each other apart? Scientists postulated the issue. How did they try to explain this phenomenon?
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