Chem 120
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Ch 8 and 9 Practice Problems - KEY
The following problems are intended to provide you with additional practice in preparing for the exam.
Questions come from the textbook, previous quizzes, previous exams, and other sources. Solutions are
supplied in a separate document.
1. Magnetic quantum number cannot have which of the following values (-1, 1, 0, -1/2, 2) when the
principle quantum number is equal to 3.
Answer: -1/2
2. How many core and valence electrons do the following elements have?
a. F
b. Cs
c. Br
d. Cr
e. Se
f. B
3. The average C-C bond energy is 347 kJ/mol. Calculate the wavelength of the photon with the
minimum necessary energy to break this bond.
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4. Which of the following are isoelectronic?
Na+, P3-, Cr6+, Ag+, Ca2+
Answer: P3-, Cr6+, Ca2+
5. Identify the atom or ion following with following ground state electron configuration:
a. the atom with [He] 2s2 2p4
b. the +1 cation with [He] 2s2 2p6
c. the atom with [Ar] 4s2 3d10 4p3
d. the +2 cation with ground state electron configuration [Ar] 3d2
e. the +1 cation with [Ar] 3d5
6. Radar guns used by law enforcement utilize the “K-band” which operates at 22.235 GHz. Find the
wavelength (in nm) and energy of a photon of this electromagnetic radiation. (1 GHz = 1 x 109 Hz)
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7. Which of the following sets of quantum numbers are not allowable based on the ground state
electron configuration for the elements and ions below. (Check the box on the right for all that apply.)
n
l
ml
ms
Check below for sets of
quantum numbers not
allowable.
Te
4
1
-2
+1/2
X
Ca
2
1
-1
+1/2
N3-
3
0
0
+1/2
Br-
3
2
-2
+1/2
V
2
2
0
-1/2
X
X
8. Ozone (O3) is important to humans because it prevents a portion of the ultra-violet light from the Sun
from reaching the earth’s surface. UV light is absorbed by ozone which is subsequently converted to O2
and an oxygen atom as in the reaction below. The bond dissociation energy of that reaction is given as
its Hrxn.
O3(g) + hv  O2(g) + O(g) Hrxn = 592.1 kJ/mol
What is the wavelength of light required to break down ozone?
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9. In the ionization reaction below, the electron is removed from the nucleus. The asterisk on the
reactant denotes that the electron was not in the ground electronic state. Determine the energy level
the electron was in before it was removed.
He+*(g)  He2+(g) + e-
Hrxn = 328.05 kJ/mol
10. A single pulse of a laser yields an average of 3.00  1018 photons with  = 433 nm. What is the
maximum number of Joules (J) that could be absorbed from 3130 laser pulses?
11. Which of the following has the greatest Zeff?
N, P, Na, Cl, B
Answer: Cl
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12. How many electrons in an atom can have each of the following quantum number or sub level
designations?
a. n =2, l = 1
b. 3d
c. 4s
d. n = 2, l =1, ml = 0
e. 3p
13. Write the full set of quantum numbers for the following:
a. the outermost electron in a K atom
b. the electron gained when Cl becomes Clc. the electron lost when Ni becomes Ni+
d. the outermost electron in Cs
e. the first electron added to the 3rd energy level into the ground state electron configuration of P.
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14. Identify if the atom or element based on the orbital diagram and identify if it is the ground state or
an excited state electron configuration.
a.
b.
atom
c.
+2 ion
d.
atom
+2 ion
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15. To which orbital (1s, 2s, 2p, 3d, 4f) does the radial probably diagram correspond?
Answer: 2s
16. Arrange the following in order of increasing atomic size:
a. N, B, F
b. Br, Se, Rb
c. As, Sn, Sb
d. Sn, Te, Sr
e. Mg, K, Ca
17. Which of these K, Ca, or Sc will have the largest IE2?
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18. Write the ground state electron configuration when the following atoms become ions in ionic solids.
a. Rb
b. S
c. Cl
d. Ca
19. Which of the following are paramagnetic? Ag+, Ti2+, Zn2+, Co3+, Cl, F-, Be, Cs+
20. Place the following in order of increasing size: Li+, Rb+, F-, Ba2+, S2-, Na+, O2-, Br-, Se2-, K+.
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21. Calculate the wavelength of light emitted/absorbed for the following transitions:
a. H atom n = 1 to n = 3
b. He+ n = 5 to n = 4
c. H atom n = 5 to n = 2
d. He+ n = 6 to n = 3
22. A rainbow forms when sunlight is separated into its constituent colors in a raindrop. Your eye can
only see electromagnetic radiation between 400 and 760 nm. If you could see infra-red radiation, where
would you find it in the rainbow?
A.
B.
C.
D.
It would be next to red.
It would be next to violet.
The sun doesn’t emit infra-red radiation, so it would not be present.
It would only be visible on a cloudy day.
Answer: A
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23. Give the full electron configuration for the following atoms. In the right hand column, provide the
number of valence electrons for each configuration
Electron configuration
Mg
S
Ti
F
2
2
6
2
1s 2s 2p 3s
1s2 2s2 2p6 3s2 3p4
1s2 2s2 2p6 3s2 3p6 4s2 3d2
1s2 2s2 2p5
# of valence electrons
2
6
4
7
24. How many orbitals in an atom can have the following designations? How many electrons can be in
each of these subshells?
a. 4p
b. 3d
c. 6s
d. 4f
25. Are the following combinations of quantum numbers allowed?
a. n = 2, l = 2, ml = +1
b. n = 1, l = 0, ml = 0
c. n = 3, l = 1, ml = -1
d. n = 2, l = 0, ml = -1
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26. How many electrons can have the following sets of quantum numbers?
a. n = 4, l = 2
b. n = 1, l = 0, ml = 0 , ms = -1/2
c. n = 5, l = 1, ml = 1
d. n = 3, l = 0
28. Carbon monoxide (CO) bonds irreversibly to hemoglobin which prevents O2 binding necessary for
sustaining human life. The hemoglobin-CO bond absorbs infrared radiation at 1953 cm-1. (The units are
the reciprocal of the wavelength in cm.) Calculate the frequency (in Hz) and the energy photon of light
for this radiation.
29. Based on how the periodic table is organized, atomic radii vary across a period (from left to right)
and down a group. Which of the following answers gives the correct relationship?
A.
B.
C.
D.
Atomic radii decrease down a group; atomic radii increase across a period.
Atomic radii decrease down a group; atomic radii decrease across a period.
Atomic radii increase down a group; atomic radii increase across a period.
Atomic radii increase down a group; atomic radii decrease across a period.
Answer: D
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30. Radio signals from Voyager 1 in the 1970s were broadcast at a frequency of 8.4 GHz. On Earth, this
radiation was received by an antenna able to detect signals as well as 4 x 10-21 W. How many photons
per second does this detection limit represent?
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