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Homework Help: Hydrogen Electron Transitions (Allowed/Forbidden)

  1. Apr 25, 2016 #1

    A R

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    1. The problem statement, all variables and given/known data
    Determine if the electron transitions are "allowed" or "forbidden" using the transition rules:
    i. 2p→2s
    ii. 1s→2p
    iii. 3d→2p
    iv. 3d→1s
    v. 4s→2p

    2. Relevant equations
    Δl = ±1, Δml= 0, ±1
    E = (-2.18*10-18eV)(1/n12 - 1/n22)

    3. The attempt at a solution
    I know iv. is forbidden because Δl is greater than 1, but what about the others? If i. is allowed then the energy is 0eV, which I think is not possible because photos are emitted. May anyone please offer a brief explanation to why it is allowed?
    Last edited: Apr 25, 2016
  2. jcsd
  3. Apr 25, 2016 #2

    Simon Bridge

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    Science Advisor
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    Just write out the angular momentum and energy (quantum number) changes for each transition, and, as you have been doing, check the numbers against the rules. It is usually easier to think in terms of eliminating the transitions that are not allowed.

    Good observation that (i) violates conservation of energy.
  4. Apr 26, 2016 #3

    A R

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    Great, I will follow your steps! I did not know whether (i) is allowed to forbidden, but the explanation is sensible as I did not know it is possible for it to emit photons but with 0eV of energy. Thank you, Simon.
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