Chemistry and Organic Chemistry Page 6 Question

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jpetrera
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Joined: Mon Jan 15, 2018 5:15 pm

Chemistry and Organic Chemistry Page 6 Question

Post by jpetrera » Mon Jan 15, 2018 5:21 pm

On page 6 for the Rydberg formula, the prompt says ni=4 and nf=2 but then goes on to set ni=2 and nf=4. Am I seeing this correctly or am I mistaken?
NS_Tutor_Andrew
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Re: Chemistry and Organic Chemistry Page 6 Question

Post by NS_Tutor_Andrew » Tue Jan 16, 2018 1:35 pm

Hi jpetrera,

Thanks for the question! You are seeing that correctly and we will make a note to fix it in the next edition. However, an interesting fact is that for the purposes of the MCAT, you can often set up the Rydberg equation in whichever way will make the math easier for you to do, because the absolute magnitude is the same either way -- that is, the same amount of energy is absorbed/released as the electron is excited/de-excited. We can confirm this fact in this example: 1/16 - 4/16 = -3/16, while 4/16 - 1/16 = 3/16. Usually, the Rydberg equation is set up to model energy release as an electron drops down from a higher orbital to a lower orbital, with the final orbital given first (1/nf^2 - 1/ni^2), and this results in a positive energy for the photon that is emitted. Flipping it will get us a negative energy, which by normal convention refers to a photon being absorbed to excite an electron. However, almost always for the MCAT, we can use the context of the problem to tell us whether we are talking about the energy being emitted in the form of a photon or the energy being absorbed from a photon, and our main use for the Rydberg equation is just to calculate the numerical value.

Hope this helps, and thanks again for the excellent question.
Andrew D.
Content Manager, Next Step Test Prep.
jpetrera
Posts: 8
Joined: Mon Jan 15, 2018 5:15 pm

Re: Chemistry and Organic Chemistry Page 6 Question

Post by jpetrera » Tue Jan 16, 2018 1:52 pm

Thank you very much!
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