CHEM 110
Last Name
Professor BEAMER
First Name
Which lab section are you in?
(Circle One)
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M
W
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HOMEWORK SET 4
Atomic Structure (Part 1): Models of the Atom
Atomic Number (Z), Mass Number (A), Isotopes, #p+, #e−, and #n0
Atomic Mass
GENERAL INSTRUCTIONS
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Do not wait the night before the assignments are due to begin them.
Turn this in separately from Homework Set 3.
HW3 and HW4 are due on Wednesday (9/30) – noon.
You will need your textbooks to do the reading for this assignment.
You can give the assignment to me beforehand, or get it to my office (Room 1843).
READING
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Chapters 4.1 through 4.5
Warning: You will not be able to do Question 6 unless you read ahead or wait until the lecture on Monday.
Part 1: Models of the Atom
1)
According to Dalton’s Atomic Theory: “An element is composed of tiny, indivisible, indestructible
particles called atoms.” In three sentences or less, explain why the Cathode Ray Tube Experiment
refutes (invalidates) this part of Dalton’s Atomic Theory. Note: You do not need to explain the
experiment itself...just state why it refutes this particular statement.
2)
According to Dalton’s Atomic Theory: “All atoms of an element are identical and have the same
properties.” Recently in class, we have learned a vocabulary word that refutes this part of Dalton’s
Atomic Theory.
2a)
Write the vocabulary word:
2b)
Copy the textbook’s definition of the vocabulary word, and state the page number where
you found it.
Page 1 of 8
CHEM 110
3)
In three sentences or less, explain how the Plum Pudding Model of the Atom and the Nuclear Model
of the Atom differ.
4)
In two sentences or less, explain how the Nuclear Model of the Atom and Bohr’s Model of the
Atom differ.
5)
In two sentences or less, explain how Bohr’s Model of the Atom and the Quantum Model of the
Atom differ.
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CHEM 110
6)
Using the diagrams below, explain the process of “light by emission.” Use the following terms in your explanation: energy, valence
electron; energy levels; ground state; excitation (or excited); excited state; relaxation (or relaxes); and photon. (Again, simply use the
terms; you do not need to define them). You can mark on the diagrams themselves and/or write your explanation underneath. Note:
atoms and electrons are not drawn to scale.
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CHEM 110
Composition of Various Isotopes – Table 1
Isotope
Atomic
Symbol
Atomic
Number (Z)
7)
Mass
Number
(A)
Number of
Protons
34
16
8)
9)
Number of
Electrons
Number of
Neutrons
20
24
Zinc-64
10)
9
11)
11
10
23
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CHEM 110
Composition of Various Isotopes – Table 2
Atomic
Symbol
12)
13)
14)
44
20
Isotope
#p+
#e–
A
Z
Ca
Strontium – 86
36
47
81
15)
16)
#no
76
137
53
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CHEM 110
Composition of Various Isotopes – Table 3
#e–
A
Atomic
Symbol
Z
#p+
#no
Iridium-193
17)
18)
Isotope
15
16
115
50
19)
20)
130
21)
23
Sn
56
11
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CHEM 110
Part 3: Atomic Mass
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Determine the atomic mass (in amu), given the information in the following problems.
You must show your work, including units through every step.
Final answer must have the correct number of significant digits.
I can word these questions in several ways, so learning to recognize how the percentages and the mass
numbers “match up” in the question is very important.
I have included a sample problem (color-coded to help you). Please do not color code your own
answers. You don’t have to line up the numbers exactly the same way that I do. However, you must
show the set up
EX)
Indium (In, atomic number 49) has two naturally occurring isotopes: indium-113 and indium-115.
The natural abundance of each isotope, respectively, is 4.290% and 95.71%. Determine the atomic
mass of indium. Compare it to the value on the periodic table to verify your answer.
Solution
STEP 1
STEP 2
(113 amu × 4.290%)
+
(113 amu × 0.04290)

(115 amu × 95.71%)
+
(115 amu × 0.9571)

+
004.847
amu
110.1
amu
114.9
amu
On the periodic table Indium (In) has an atomic mass of 114.8 amu. My answer is acceptable.
22)
Neon has three naturally occurring isotopes:
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Neon-20, natural abundance is 78.99%
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Neon-21, natural abundance is 0.2700%
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Neon-22, natural abundance is 9.25%
Determine the atomic mass of neon, and compare your value to the atomic mass on the periodic
table to validate your answer.
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CHEM 110
23)
Antimony (Sb) has two naturally occurring isotopes. Antimony-121 has a natural abundance of
57.21%. Antimony-123 has a natural abundance of 42.79%. Determine the atomic mass of
antimony, and compare your answer to the value on the periodic table for validation.
24)
Iron has four naturally occurring isotopes: Iron-54, Iron-56, Iron-57, and Iron-58. The natural
abundance of each isotope, respectively, is 5.845%, 91.754%, 2.119%, and 0.2820%. Determine
the atomic mass of iron, and compare your answer to the atomic mass value for iron on the periodic
table for validation.
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