Hydrogen Electron Transitions (Allowed/Forbidden)

AI Thread Summary
The discussion focuses on determining whether specific electron transitions in hydrogen are "allowed" or "forbidden" based on transition rules. The transitions under consideration include 2p→2s, 1s→2p, 3d→2p, 3d→1s, and 4s→2p. It is noted that the transition 3d→1s is forbidden due to a violation of the angular momentum change rule (Δl > 1). There is confusion regarding the 2p→2s transition, which is suggested to be allowed despite concerns about energy conservation, as it can theoretically emit photons with zero energy. The conversation emphasizes the importance of analyzing angular momentum and energy changes to classify the transitions correctly.
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Homework Statement


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

Homework Equations


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

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?
 
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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.
 
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Simon Bridge said:
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.

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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