An electron changes from an n = 2n=2 to an n = 6n=6 energy state. What is the energy of the photon in joules?
1 Answer
Explanation:
The question wants you to determine the energy that the incoming photon must have in order to allow the electron that absorbs it to jump from
A good starting point here will be to calculate the energy of the photon emitted when the electron falls from
1/(lamda) = R * (1/n_f^2 - 1/n_i^2)1λ=R⋅(1n2f−1n2i)
Here
lamdaλ si the wavelength of the emittted photonRR is the Rydberg constant, equal to1.097 * 10^(7)1.097⋅107 "m"^(-1)m−1
Plug in your values to find
1/lamda = 1.097 * 10^7color(white)(.)"m"^(-1) * (1/2^2 - 1/6^2)1λ=1.097⋅107.m−1⋅(122−162)
1/lamda = 2.4378 * 10^6 color(white)(.)"m"^(-1)1λ=2.4378⋅106.m−1
This means that you have
lamda = 4.10 * 10^(-7)color(white)(.)"m"λ=4.10⋅10−7.m
So, you know that when an electron falls from
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To find the energy of this photon, you can use the Planck - Einstein relation, which looks like this
E = h * c/lamdaE=h⋅cλ
Here
EE is the energy of the photonhh is Planck's constant, equal to6.626 * 10^(-34)color(white)(.)"J s"6.626⋅10−34.J s cc is the speed of light in a vacuum, usually given as3 * 10^8 color(white)(.)"m s"^(-1)3⋅108.m s−1
As you can see, this equation shows you that the energy of the photon is inversely proportional to its wavelength, which, of course, implies that it is directly proportional to its frequency.
Plug in the wavelength of the photon in meters to find its energy
E = 6.626 * 10^(-34) color(white)(.)"J" color(red)(cancel(color(black)("s"))) * (3 * 10^8 color(red)(cancel(color(black)("m"))) color(red)(cancel(color(black)("s"^(-1)))))/(4.10 * 10^(-7) color(red)(cancel(color(black)("m"))))
color(darkgreen)(ul(color(black)(E = 4.85 * 10^(-19)color(white)(.)"J")))
I'll leave the answer rounded to three sig figs.
So, you can say that in a hydrogen atom, an electron located on