Rydberg Formula

[clairehathaway 2J]

I was trying to calculate the energy of light absorbed from an electron (in a hydrogen atom) going from n=2 to n=4.
In order to solve it I used the equation and plugged in n=2 and then n=4 and then used plugged those results into the deltaE = Efinal - Einitial (deltaE = E(4) - E(2)). When I did that I did not get the right answer so then I tried using the Rydberg equation with n1=4 and n2=2 () and then used plugged the answer I got from that into E=hv, and that gave me the right answer.
I thought that either way would give you the same answer because I thought that would give me the energy at certain n levels and then I could subtract them to get the amount absorbed. Why doesn't that equation work but the Rydberg equation does?

[Kailani_Dial_2K]

So did you do final minus initial? You should have plugged in n=4 first and then subtracted n=2 from that value as n=2 is your final value. I would try this and then check your answer again. The equations should give you the same outcome as one is derived from the other.

(-hR/16) - (-hR/4) should give you the energy of the electron.

From the energy of the electron you have to find the energy of the photon by multiplying your answer by -1.

You know have the energy of the Photon so you should then use E=hv and that should give you the right answer. I hope this helps

[Astha Sahoo 3I]

I agree with what was said above! Also make sure you have all the signs(+/-) the right way since that messed me up the first couple of times I did the problem.

[Jason_Glass_2L]

To add on, I realized you said that you plugged in n=4 into n1 and n=2 into n2. Just remember for the Rydberg equation if the negative isn't factored out with the R constant in the equation, the n that comes first in the equation will be your starting n level and the n that comes second in the equation will be your final n level.