Hydrogen and energy levels, quantized packets of light

[MCAT guy]

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This is a concept that I know and can repeat... but I really don't understand. If I were to teach someone, I would just have to repeat memorized words.

So... here is a question:

Which of the following observations leads to the conclusion that energy levels are quantized?

• A. sample always absorbs same amount of light
• B. Sample always absorbs same color of light
• C. Sample emits different frequencies at different temp
• D. Sample emits difference frequencies at different conc

So samples can absorb different amounts of light, what does this mean anyway. Someone explained to me that light is quantized, so I can think of that as being 1, 2, 3, 4 (instead of 1.1, 1.4, 2.7, etc), which makes sense but what does that have to do with this idea?

So are we saying that hydrogen will always absorb yellow light or something? Isn't it true that I could use violet light to get the electrons to an even higher energy state?

And intensity just means like a really bright yellow light versus a really dim yellow light, correct? So if I used higher intensity yellow light on a sample that absorbs yellow light, then it would just absorb more of the packets?

These ideas are so abstract to me. I need pictures or something!

 

[lorenzomicron]

the correct answer is B. always the same colors.
the reasoning here is that colors of light correspond to its frequencies. using the function E=h*f where h is the planck constant, it is seen that the frequency corresponds to some particular energy of a photon, i.e. a photon's energy depends on its frequency.

thus, in an atom for instance, its energy levels of its electrons are quantized; in semi-quantum mechanics (bohr model), this energy level of the electron is given by E= 13.6ev/n^2. if we look more into this, then we see that we can only input a particular energy into the system, which corresponds to n=1,2,3,4,5, etc.
thus, we can jump particular electrons from one energy level to others, according to an energy difference between these n, namely deltaE= 13.6[1/nf^2 - 1/ni^2].

so, if we want to jump an electron from one n to another, we can determine the necessary photon as follows:

h*f= 13.6[1/nf^2 - 1/ni^2]

so, above talks about quantization in energy. thus, a sample of matter will only absorb certain energies, i.e. certain frequencies of light, dependent on its electron structure (etc).

let's examine the answer choices:

A. sample always absorbs same amount of light
amount of light doesnt have anything to do with energy of the photon; it has to do with intensity of the light; a sample can absorb more or less amount of light and emit more or less photons. so this doesnt matter.

B. Sample always absorbs same color of light
yep, this corresponds to our model of quantization. in particular, all materials have distinctive color absorption; this is the basis of spectrography, which you may have carried out in chemistry to identify various elements.

C. Sample emits different frequencies at different temp
temperature shouldnt affect frequency in our model;

D. Sample emits difference frequencies at different conc
nope. the last part of our model is that we give electrons energy to excite them upon doing doing so, the electrons eventually fall back to their ground state. to do so, they emit photons, i.e. emit light. but, they would only be able to emit the quantized photons they absorbed. thus, the frequencies should be the same, neverminding the concentration which affects amount of light emitted, not its frequency or energy.