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B Free electrons

  1. Nov 28, 2016 #1
    So, as far as I know free electrons are just electrons that have been 'released' from the shell of an atom and can now move. If this is true, what is it that causes the electron to become free in the first place?

    Thanks in advance to any answers ☺
     
  2. jcsd
  3. Nov 28, 2016 #2

    berkeman

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    https://en.wikipedia.org/wiki/Free_electron_model

    :smile:
     
  4. Nov 28, 2016 #3
    Also look at
    https://en.wikipedia.org/wiki/Electronic_band_structure

    An atom has discrete energy levels. A large molecule has many more energy levels, since there are many degrees of freedom. When there are many energy levels close to each other, they form a band. Electrons can easily move between states in a band.
     
  5. Nov 28, 2016 #4
    I guess a truly free electron is a mathematical approximation.
     
  6. Nov 28, 2016 #5
    So, say you have a block of Copper, the free electrons are just jumping from shell to shell of the atoms that make up that copper??
     
  7. Nov 28, 2016 #6
    The outer electrons orbit the entire molecule as a whole, I think.
     
  8. Nov 28, 2016 #7

    Drakkith

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    Assuming you're referring to free electrons as the valence electrons in a metallic object, then they occupy states in which they are shared with the entire block of copper. They no longer occupy an orbital around a single nucleus.
     
  9. Nov 28, 2016 #8

    ZapperZ

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    So, already your starting premise is wrong.

    In a solid, there are stuff that can't be found in isolated atoms, such as energy BANDS. At the simplest level, these are what caused a solid to be a conductor, semiconductor, insulator, etc. The conduction electrons do not belong to any particular atom. So in a photoelectric effect, the electrons being released from the solid are not "... electrons that have been 'released' from the shell of an atom...".

    This is why Solid State Physics is different than atomic physics or molecular physics.

    Electron emission can be as simple as having enough energy to overcome any attractive potential or barrier, or it can be as quantum-mechanical as tunneling through the barrier.

    Zz.
     
  10. Nov 28, 2016 #9

    Wow - it's crazy how much of what I'm taught is wrong. Thanks for clearing that up for me ☺
     
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