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Rydberg's Formula

Posted: Tue Oct 10, 2017 10:13 pm
In the video module under "Atomic Spectra," it discusses how electrons continually become "more negative" when they go down energy levels and emit more photons. When discussing Rydberg's formula, we were given -R=[(1/n1^2)-(1/n2^2)]. In the book, the same formula is given but just without the negative sign in front of the R. Can someone clarify when we would use the formula with the negative sign and when we would use the formula without the negative sign?

Re: Rydberg's Formula

Posted: Tue Oct 10, 2017 10:34 pm
In my opinion, we use the formula with the negative sign when we calculate the energy absorbed or emitted. That is the energy difference between two energy levels. We use the formula without the negative sign when we deal with the frequency associated with the light. Because energy emitted is negative, but we need a positive frequency. So the negative sign is not included in this case.

Re: Rydberg's Formula

Posted: Fri Oct 13, 2017 7:45 pm
Yeah the formula used in the video is v = -R((1/n1^2) - (1/n2^2). This is for calculating the energy emitted. For example, if there is a jump from level 4 to level 2, you would used the formula to calculate the frequency.

Re: Rydberg's Formula

Posted: Fri Oct 13, 2017 9:16 pm
We use the formula with the negative to calculate ΔE. For example, if we were to calculate the energy emitted from an electron from the energy level of 4 to an energy level of 2, ΔE would be negative. However, if we were to use the formula with the negative to calculate the energy absorbed from a photon to move an electron from the electron level of 2 to the electron level of 4, ΔE would be positive. The negative indicates the direction.

Keep in mind that frequency and wavelength are always positive. If a negative ΔE was used to calculate frequency, take the absolute value.

Hope this helped!