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They thought that the electron should fall into the nucleus?

  1. May 18, 2015 #1
    Hopefully I have this right. When they discovered the electron, they immediately realised that the electron should get sucked into the nucleus due to the electromagnetic force from the opposite charges. Why didn't they assume that the electron could orbit the nucleus to cancel out the electromagnetic force if it was travelling fast enough, just like the Moon orbits the Earth to cancel out the gravity?

    The reason why I ask this in the homework section is because it is in my textbook. I am not sure if I will have to know this.
     
  2. jcsd
  3. May 18, 2015 #2
    Probably because an electron is not a discrete object like a planet and it doesn't orbit a nucleus. A more accurate description of what's happening is that the electron is vibrating around the nucleus. Think of the electron as a wave, not a particle in your case.
     
  4. May 18, 2015 #3

    Borek

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    Staff: Mentor

    Accelerating charge emits electromagnetic radiation and loses energy.
     
  5. May 18, 2015 #4

    Borek

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    Question is not about "what the electron is", but about "why it can't be explained in the terms of orbiting the nucleus". Once we knew it can't we had to look for other explanations, but the first rule in science is - use Occam's razor. If something can be explained using known phenomena/laws/effects there is no need for new ones.
     
  6. May 18, 2015 #5
    Thank-you so much! They mentioned an "infinite energy" issue that I didn't understand either, but your post clears that up for me too.
     
  7. May 18, 2015 #6

    Borek

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    It is the same problem, just expressed in a different way.
     
  8. May 18, 2015 #7

    James Pelezo

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    The electron doesn't fall into the nucleus b/c it can absorb and release energy. I'd suggest reviewing the Bohr Model of the atom and why Neils Bohr related the bright line emission spectrum of Hydrogen to electrons orbiting at 'discrete' distances from the nucleus. Basically, electrons absorb energy, jump outward from a low energy orbit to a higher energy orbit and then falls back to lower energy levels. During the 'electron transition' from a higher energy orbit to a lower energy orbit, light energy (photons) are emitted. If they stop at the n = 2 energy ( or, L-shell of the atom ) they will emit visible radiation which can be viewed using a diffraction grating or prism. Hydrogen gives 4 visible spectra lines, each having a 'discrete' wavelength. This means that the electron during energy level transitions will reside at a specific distance (discrete average, i.e., principle quantum number (n) according to Quantum Mechanics) from the nucleus. The electron starts its transition in a higher energy orbital, then it is in a lower energy orbital. It doesn't stop in between, or give evidence that it passed through the 'in between'. Such is called 'quantization,' or more commonly referred to as a 'quantum leap'. If they resided anywhere within the atomic volume, examination of the EMR Spectrum would be a Continuous Spectrum like the rainbow. Colors of the rain bow: ROY G BIV. From low energy to high energy ... Red, Orange, Yellow, Green, Blue, Indigo & Violet.

    P.S. 'Infinite Energy' is the 1st (and only) Ionization Energy of the Hydrogen Atom. ∆Ei-1 = 2,8 x 10-18 Joule[ (1/n2)i - (1/n2) ] = 2.8 x 10-18 Joule[ (1/n2)i ] where (1/∞2) = 0. Then ionization from the ground state configuration, n = 1 => ∆Ei-1 = 2.8 x 10-18 Joule/H-atom = [(2.18x10-18 x 6.02x1023) / 1000]Kj/mole = 1312 Kj/mole.
     
    Last edited: May 18, 2015
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