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4.15: Atomic Nucleus

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     Science is like a jigsaw puzzle
    Figure \(\PageIndex{1}\) (Credit: Charles Hamm; Source: in new window); License: CC ​​​​​​​by 3.0(opens in new window))

    How is science like a jigsaw puzzle?

    Many people enjoy putting jigsaw puzzles together. As the different pieces go together, the picture begins to become clearer. When the puzzle is completed, you see that what had been a confused collection of individual components that made little or no sense by themselves fit together to give a clear picture.

    Science works the same way as a jigsaw puzzle. Different researchers make individual discoveries that answer a specific question or questions. When enough data are gathered, we get a better understanding of a process or a structure. The experiments of Crooke, Millikan, Rutherford, and many others gave us pieces of the puzzle that is the atomic nucleus.

    Different Models of the Nucleus

    After the electron and proton were discovered, people began to try to build a picture of the atom. The Thomson model had electrons mixed in with a positive core of some sort that provided electrical neutrality. Rutherford showed that this model was incomplete. His picture of the atom involved a small solid core that alpha particles could zoom past with very few collisions. So the picture of the atom became a little clearer – electrons surrounded a very small core nucleus. The discovery of the neutron helped fill out the picture even more. We now have protons and neutrons in a concentrated center of the atom with electrons surrounding the nucleus.

    One problem still existed. We have a number of positively charged protons in the nucleus. Why don't they push each other apart? Physicists postulate a strong nuclear force that acts at very short distances. At these distances the attraction between protons is greater than the force causing the positive charges to push each other away. Neutrons are also involved in this process somehow. So the strong force holds protons together, it holds neutrons together, and it causes protons and neutrons to be attracted to one another.


    • Rutherford proposed a model of the atomic nucleus which had a solid core.
    • Physicists postulate a strong nuclear force holds the protons and neutrons together in the nucleus of the atom.


    1. How did Rutherford change our thinking about atomic structure?
    2. What is our current picture of the atom?
    3. Why is the presence of positively charged protons a problem with current models of the atom?
    4. How do we explain why the nucleus does not fall apart?

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