3
$\begingroup$

So, my proff. says that when an electron in the $1s$ orbital of the H-atom is given an energy, it can rise to the $2s$ orbital state. This is all good, but the question that I want to ask is, if an electron in the $2s$ state is given some energy, can it rise to the $2p$ state? The reason I am asking is because energy conservation is obviously taken care of by $$\hbar\omega=E_{2p}-E_{2s}$$ But, is conservation of angular momentum taken care of? Since the value of the orbital angular momentum quantum number $l$ would have to shift from $l=0$ to $l=1$. This, I am guessing, would cause a shift in the angular momentum of the electron and the conservation of angular momentum would be lost. So, is the transition from the $2s$ to the $2p$ orbital not possible? Or how does this transition take place? Because, as far as I know, photons would have a momentum equivalent to $p=\hbar\omega/c$, but do they have angular momentum? I mean, I'm sorry to sound like a noob, but I am an engineer who's studying physics, so maybe I am just looking at things differently. Do the laws of conservation of momentum not hold at all at these levels?

$\endgroup$
1

1 Answer 1

3
$\begingroup$

Angular momentum, as you correctly note, must be conserved. An emitted or absorbed particle will take care of the unaccounted angular momentum. And because of this condition, selection rules apply, allowing only certain transitions, or making some extremely unlikely and only driven by different interaction mechanisms.

From the Wikipedia page I linked:

The emitted particle carries away an angular momentum λ, which for the photon must be at least 1, since it is a vector particle.

Other details and calculations can be found there.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.