Really confused on some multiple choice questions. Please Help!

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JasonNovik3A
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Joined: Fri Sep 29, 2017 7:07 am

Really confused on some multiple choice questions. Please Help!

Postby JasonNovik3A » Mon Oct 16, 2017 8:28 pm

15. In the above spectroscopic experiment what is the most unique characteristic of the observed results? Hint: What does a typical spectrum look like?

A. All wavelengths of light are absorbed or emitted. Spectrum consists of lines.

B. No wavelengths of light are absorbed or emitted. Spectrum consists of waves.

C. Only specific wavelengths of light are absorbed or emitted. Spectrum consists of lines.

D. Only specific wavelengths of light are absorbed or emitted. Spectrum consists of waves.

16. In atomic absorption (or emission) spectroscopy are all wavelengths of light absorbed (or emitted)?

Yes

No
19. When we say hydrogen atoms absorb a specific wavelength of light what do we mean? Use energy in your detailed explanation of what is being excited.

A. We mean that a photon with a specific energy lowers the energy of the electron in the hydrogen atom to its ground state. That is, the photon's energy matches the energy difference between two electronic energy levels.

B. We mean that a photon with a specific energy absorbs the energy of the electron in the hydrogen atom to a higher energy level. That is, the photon's energy matches the energy product of the two electronic energy levels.

C. We mean that a photon with a specific energy excites the electron in the hydrogen atom to a lower energy level. That is, the photon's energy matches the energy sum of two electronic energy levels.

D. We mean that a photon with a specific energy excites the electron in the hydrogen atom to a higher energy level. That is, the photon's energy matches the energy difference between two electronic energy levels.


20. If 1 million photons in the UV region are absorbed by a hydrogen gas sample how many electrons are excited to a higher energy level?

A. zero

B. 500,000

C. 1

D. 1 million

22. In ultraviolet and visible spectroscopy what condition must occur for a photon to be absorbed?

A. The photon must be at its lowest energy state.

B. Energy of the photon must be within the energy difference between two energies that an electron can have.

C. The photon must be at its highest energy state.

D. Energy of the photon must match the energy difference between two energies that an electron can have.

For the hydrogen atom which statement is true?

A. The transition from n = 5 to n = 3 involves greater energy than one from n = 4 to n = 2.

B. The transition from n = 4 to n = 2 emits radiation of longer wavelength than the transition from n = 5 to n = 1.

C. All transitions from states for which n > 1 to the n = 1 state involve the absorption of energy by the atom.

D. A transition from n = 2 to some large value of n corresponds to the ionization energy of the H atom.

OH AND LAST QUESTION, can wavelengths be noted in negative values?!?!?!?!

Ryan Sydney Beyer 2B
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Joined: Fri Sep 29, 2017 7:07 am
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Re: Really confused on some multiple choice questions. Please Help!

Postby Ryan Sydney Beyer 2B » Mon Oct 16, 2017 9:37 pm

15. C - Only specific wavelengths of light are absorbed or emitted. Spectrum consists of lines.

This is because only certain wavelengths (and therefore frequencies) match the energy difference from one energy level to the next. So only certain wavelengths of light could possibly be absorbed / emitted. On an absorption spectrum there would be a white line on a black rectangle because the atom absorbed the light and it can't be shown on the spectrum. On an emission spectrum this would look like a dark line on a blank rectangle because it is showing the light given off by the atom.


16. No

In atomic spectroscopy, only the wavelengths of light that have energy equal to the difference between energy levels is absorbed or emitted. This is very specific and allows us to determine what certain molecules and elements are because of their unique fingerprint.


19. D

So when a hydrogen atoms absorbs an incoming photon, the only way for the atoms to take on this photon is if the energy of the photon is equal to the energy difference between energy levels. The photon entering the atom has a specific energy and if the energy of the photon matches the difference between two energy levels in this hydrogen atoms then the photon will be absorbed and the electron will be excited to that higher energy level.


20. D - 1 million

Let us just make it simple and say that there is a 1 : 1 ratio between photons absorbed by the sample and the number of electrons that could possibly become excited to a higher energy level.


22. D - Energy of the photon must match the energy difference between two energies that an electron can have.

In order for the atoms to absorb the incoming photon, the energy of the photon must be equal to the difference in energies between two energy levels for an electron. I think I already went over this concept enough in some of the previous problems.


For the hydrogen atom which statement is true? - B - The transition from n = 4 to n = 2 emits radiation of longer wavelength than the transition from n = 5 to n = 1.


I think it is important to remember in this problem that the higher up the energy level ladder you climb the closer together the energy levels become and it takes less absorption energy to jump up to the next level and therefore emits less energy when emitting a photon. So when an electron is moving from n = 4 down to n = 2 it is emitting a photon of a certain energy and the same occurs for the electron that moves from n = 5 down to n =1. So going off of what I said with the energy levels being closer together as you climb higher and being further apart as you go lower, we would know that the n = 5 to n = 1 transition is going to emit more energy than the other transition. So if the energy is greater then we know that the frequency must be higher and a higher frequency means a lower wavelength.


And no, wavelengths or frequencies can never be noted in a negative value as this is not physically possible.


This might come into play when dealing with the Rydberg formula and those negative signs but just think of what wavelength actually is and you'll know that it isn't possible to have a negative value.


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