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Chemistry F09 Student Notes 5-3 electrons in atoms
(section 5.1) Bohr Model vs. Quantum Model of atom
1. Bohr model vs. Quantum Model of Atom
a. Bohr proposed (complete key statement on p. 128):
b. How does Bohr’s proposal relate to the rungs of a ladder?
c. Draw a representation of Bohr’s proposal with up to 4 labeled energy levels.
d. Bohr’s model is convenient (and somewhat accurate) if we just consider energy levels, but not so
accurate when we consider sublevels. What is correct about Bohr’s model? What is incorrect
about Bohr’s model?
(section 5.3) EM Wave Refresher: p. 138-139
1. Light, or electromagnetic radiation (EM), consists of much more than what can be detected by the human
eye
a. Draw the two waves in Figure 5.9 p. 138, labeling wavelength, frequency, crest, trough, and
amplitude.
b. Which of the two waves drawn above has a longer wavelength? Higher frequency?
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c. Humans detect wavelengths between 0.000 000 4 m and 0.000 000 7 m (400 nm to 700 nm) and
our brain interprets these wavelengths into colors. We cannot see all forms of light.
d. White light consists of all forms of visible light. This can be separated using a diffracting tool
(separates light by bending the light), such as a prism (rainfall/sunlight = rainbow; sun/curve of
earth = sunrise/sunset)
e. The EM spectrum actually ranges from 10 -14 m to 10 2 m (0.000 000 000 000 01 m – 100 m)
f.
Use F5.10 to organize the 8 areas of the EM spectrum (remember visible light!!) in order of
decreasing wavelength
g. Describe the relationship between a wave’s frequency and its wavelength.
h. Wave A has a wavelength of 1000 nm and Wave B has a wavelength of 500 nm. Which wave has
a larger frequency?
2. All waves have the following characteristics: amplitude, wavelength, and frequency
a. Which of the pair has a greater
wavelength?
 Red light or purple light
 Visible light or infrared light
 UV light or gamma radiation
b. Which of the pair has a greater
frequency?
 Red light or purple light
 Visible light or infrared light
 UV light or gamma radiation
c. As wavelength increases, frequency ___________________. This a/an _________________
relationship.
d. Frequency and wavelength are related by the following equation:
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(section 5.3) Electrons and Light Production
3. Electrons can absorb energy. This energy can be in the form of radiant, potential, or kinetic. When an
electron absorbs enough energy all at once, the electron can move into a higher energy level (move
away from the nucleus). This is called the “excited state”. Electrons then emit the EXACT SAME
AMOUNT of energy that was absorbed and fall back to the original energy level (“ground state”). This
emitted energy is always in the form of Electromagnetic Radiation.
a. If the emitted EM radiation is between 0.000 000 4 m and 0.000 000 7 m, human eyes detect it
as visible light (EX: flame tests)
b. However, electrons can emit EM radiation well beyond the visible spectrum.
c. Draw an orbital diagram and electron configuration and Bohr model to demonstrate ground state
and excited state of an electron in an atom of Lithium.
4. To repeat: If an electron absorbs a quantum of energy it can move up an energy level, called the
______________________ state. The electron then emits the exact amount of energy that was
absorbed in the form of light, which causes the electron to fall back to the original position, or return to
its ___________________________ state. The emissions of energy in the form of light (or EM
radiation) can recorded as Atomic Emission Spectra.
a. The farther an electron falls, the higher the frequency of EM radiation emitted (examine F5.14).
Which fall is further—from n = 2 to n = 1 or from n = 3 to n = 2?
b. Absorption Spectra: shows which light is absorbed by electron when climbing (looks like a
rainbow with lines of black—missing light). Draw the absorption spectra for Hydrogen.
c. Emission Spectra: shows the light being given off by the electron when falling (looks like a black
background with lines of color). Draw the emission spectra for Hydrogen.
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d. Atomic Emission Spectra (p. 141, F5.12) are unique for each element, and can be thought of as
an elemental fingerprint. Since our eyes cannot separate the colors like diffraction tools can, we
see a blend of these emissions. (you should be putting together how the flame tests worked…)
5. Go back to 5.1, p.128-129—ladder analogy
a. An electron must absorb enough energy all at once to move to another energy level, otherwise it
will not advance. Think of a ladder or an elevator—you would never want to stop in between
rungs or floors.
b. A quantum of energy is the amount of energy required to move an electron from one energy
level to another energy level (quantum – singular; quanta-plural)
c. Examine the spacing of the rungs of the ladders in F5.3, then compare these to spacing of the
energy levels of an atom as shown in F5.14 p.143. Where is the biggest gap? What happens to
the distance between energy levels as energy level increases?
Relating Wave Characteristics, Energy, and Heisenberg
6. An equation can be used to relate the frequency of the EM radiation emitted by the electron to the
amount of energy emitted by the electron. That is, one can relate a wave’s frequency to the amount of
energy being transmitted by the wave using the following equation:
7. What is the relationship between a wave’s (light) frequency and energy? Wavelength and energy?
8. Wave A has a wavelength of 700 nm and Wave B has a wavelength of 900 nm. Which wave has more
energy?
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9. Wave A has a frequency of 3 x 10 -2 Hz and Wave B has a frequency of 3 x 10 -1 Hz. Which wave has
more energy?
10. Heisenberg Uncertainty Principlal:
a. State the principal:
b. Explain why it is true (think about how we “look” at particles)
1. As an electron “falls” from a higher energy level to a lower energy level, energy is emitted as light. You could generalize, the
greater the difference in energy levels, the (more/less) energy emitted.
2. Electron A falls from energy level 5 to energy level 4, and electron B falls from energy level 3 to energy level 2.
a. Which electron will release light with more energy?
b. Which electron will release light with a larger wavelength?
c. Which electron will release light with a larger frequency?
d. Which electron will produced light that is closer to the red end of the visible spectrum?
3. Electron C climbs from energy level 3 to energy level 4, and electron D climbs from energy level 1 to energy level 2.
a. Which electron will need to absorb light with more energy?
b. Which electron will need to absorb light with a larger wavelength?
c. Which electron will need to absorb light with a larger frequency?
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4. Electrons can move up and move down energy levels. Which process releases energy and why?
5. In the flame tests, you observed colorful flames of otherwise colorless appearing liquids. Explain the process by which these
colors were produced. In your response, include the movement of electrons, the source of energy that excited the electrons,
and the process by which electrons produce visible light.
6. True or False: When an electron moves back down energy levels, it emits as much EM energy as it took to move up the
energy levels.
7. True or False: Electrons can only move up energy levels by absorbing light from the visible spectrum.
8. True or False: Electrons can only emit light from the visible portion of the EM spectrum when dropping energy levels.
9. True or False: Electrons will only absorb photons (energy packets) that are exactly the right amount of energy needed to get
them to an energy level. Hmmm… the answer is TRUE! Think of elevators: You would only ride an elevator that had enough
energy to get you to a floor—you would not want to stop somewhere in between. Electrons are similar in the sense that they
will only absorb a photon if it has enough energy to get them to a level—any level. On the other hand, electrons will only emit
just enough energy to get them to go down to a level. The energy needed to move up a level is the same amount of energy
released to go in the reverse direction.
10. As the atomic number increases, so does the number of electrons. Would you expect more or less lines in the atomic
emission spectrum for an atom with a large atomic number vs. an atom with a small atomic number?
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