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In my textbook I was asked to compute the wavelength of a photon emitted as the nucleus of a Sodium atom pass from the first excited level to the base level. I got the formula itself right, but inserted the wrong difference in energy between the two levels when I checked the answer key. The number I used was 0.4 x 10^5 eV, based on the attached graph, assuming that the base level is at point 0 and the first excited level is the first line above what I assumed to be the base level (around 0.4 x 10^5 eV). The answer key uses the amount of 1.5 x 10^5 eV, based on the same graph. Was I wrong in my way of reading the graph, in the sense that the base level is not at 0, but rather the first line (around 0.4 x 10^5 eV), with the first excited level being at 2.2 x 10^5?

I need to know so that I am able to read these graphs correctly in the future.

Thank you!

enter image description here

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closed as off-topic by Emilio Pisanty, user191954, Aaron Stevens, Kyle Kanos, Jon Custer Oct 5 '18 at 18:44

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An electron in orbit around a nucleus cannot have zero energy. The ground state of Sodium (neutral) is 3s which corresponds to your latter assumption which is 0.4.

Remember that the minimum allowable state for an electron in orbit around any nucleus is an energy state with non-zero energy. To understand the quantum mechanical reasoning behind this, I suggest you read this question, where OON gives a great explanation

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    $\begingroup$ Thanks! Your answer makes sense, but what confuses me is that we are speaking specifically about the excitation of the /nucleus/, not of any electrons. Why would the same hold for the nucleus? $\endgroup$ – Pregunto Oct 4 '18 at 11:00

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