Chemistry PreAP
Atomic Structure
Homework
Packet
Name: ___________________________________Period: ___________
Chemistry Teacher:__________________
1
Isotopes
Are all atoms of an element alike?
Why?
The following activity will help you learn the important structural characteristics of an atom. How do we
classify atoms? How does the combination of subatomic particles affect the mass and charge of an atom?
xYcÿnat are isotopes? This is just a sampling of what we will address. Throughout this activity you will want
to keep both Model 1 and a periodic table handy.
Model !
Isotopes of Hydrogen
{H
Symbol
Atomic Diagram
with Name
/ Electron clond
ÿH
ÿH
/Electron cloud
Nucleus
/ Electron cloud
/_---- Nudeus
'ÿ
(protium)
Number of Protons
Cÿ
(tritium)
(deuterium)
@
Number of Neutrons 0
Isotopes of Carbon
12C6
Symbol
/
Atomic Diagram
with Name
Electron cloud
Carbon-12
Number of Protons
/Electron cloud
Carbon- 13
6
.---Electron cloud
Carbon-14
@
Number of Neutrons O
Isotopes of Magnesium
24
Symbol
12Mg
Atomic Diagram
with Name
/Electron cloud
Magnesiura-24
Number of Protons
14C
1ÿC
-
25
12Mg
...../Electron cloud
Magnesium-25
0,¢ ....
26
ÿ2Mg
/Electron cloud
Magnesium-26
©
Number of Neutrons O
Isotopes
2
,
Refer to Model 1. What subatomic particles do the following symbols represent in the Atomic
Diagrams?
,
Complete the table in Model 1 by counting the protons and neutrons in each atomic diagram.
Divide the work evenly among group members.
,
Find the three elements shown in Model 1 on your periodic table.
a. What whole number shown in Model 1 for each element is also found in the periodic table
for that element?
Hydrogen --
Carbon --
Magnesium -- 1
b. The whole number in each box of the periodic table is the atomic number of the element.
What does the atomic number of an element represent?
c. Refer to the isotope symbols in Model 1. Relative to the atomic symbol (H, C, or Mg), where
is the atomic number located in the isotope symbol?
4. Refer to your periodic table.
a. How many protons are in all chlorine (CI) atoms?
b, A student says "I think that some chlorine atoms have 16 protons." Explain why this student
is not correct.
,
Refer again to Model 1. In the isotope symbol of each atom, there is a superscripted (raised)
number. This number is also used in the name of the atom (i.e., carbon-12). It is called the mass
number.
a. How is the mass number determined?
b. why is this number called a "mass" number?
POGILTM Activities for High School Chemistry
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6. Fill in the table for Atom I and Atom II shown below.
Atom I
Atom II
Number of Protons
Number of Neutrons
Mass Number
Atom I
Atom II
m m
m
7. Refer to Model 1.
a, Which corner of the isotope symbol contains the mass number?
b. How is the mass number of an isotope expressed in the name of an atom?
8. Write an isotope symbol (similar to those in Model 1) for each of the atoms in Question 6.
9. Write the name of the atom (similar to those in Model 1) for each of the atoms in Question 6.
10. Fill in the following table.
Isotope Symbol
Atomic Number
40
19K
18
9F
16
Mass Number
Number of Protons
Number of Neutrons
15
'ÿ:ÿ11. Consider the examples in Model 1.
l/.
Do all isotopes of an element have the same atomic number? Give at least one example or
counter-example from Model 1 that supports your answer.
Isotopes
4
b. Do all isotopes of an element have the same mass number? Give at least one example or
counter-example from Model 1 that supports your answer.
12. Considering your answers to Question 11, write a definition oflsotope using a grammatically
correct sentence. Your group must come to consensus on this definition.
204_-- 82
78
208ÿ-- 204ÿ 205ph
13. Consult the following list of isotope symbols: 821"13, 35Br, 35Br, 821"t3, 7al't, 82---.
a. Which of the atoms represented by these symbols are isotopes of each other?
b. Which part(s) of the isotope symbol was the most helpful in answering part a of this
question?
POGILTM Activities for High School Chemistry
5
Extension Questions
14. Determine the number of electrons in each of the atomic diagrams in Model 1.
a. In a neutral atom, how does the number of electrons compare to the number of protons?
b. Discuss why this relationship is important in making a "neutral" atom.
15. Refer to the hydrogen isotopes in Model 1. Each isotope has a special name derived from Latin
(protium, deuterium, and tritium). What structural feature do these names refer to in the atom?
16. Can two atoms with the same mass number ever be isotopes of each other? Explain.
17. MI models have limitations. What characteristics of Model 1 are inconsistent with your under-
standing of what atoms look like?
Isotopes
6
Average Atomic Mass
How are the masses on the periodic table determined?
Why?
Most elements have more than one naturally occurring isotope. As you learned previously, the atoms of
those isotopes have the same atomic number (number of protons), making them belong to the same element, but they have different mass numbers (total number of protons and neutrons) giving them different atomic masses. So which mass is put on the periodic table for each element? Is it the most common
isotope's mass? The heaviest mass? This activity will help answer that question.
Model 1 - A Strip of Magnesium Metal
1. Write in the atomic number for each Mg atom in Model 1.
2. What are the mass numbers of the naturally occurring isotopes of magnesium shown in Model 17
3. Do all of the atoms of magnesium in Model 1 have the same atomic mass? Explain.
4. For the sample of 20 atoms of magnesium shown in Model 1, draw a table indicating the mass
numbers of the three isotopes and the number of atoms of each isotope present.
5. Which isotope of magnesium is the most common in Model 1?
6. Based on Model 1 and the table you created in Question 4, for every 10 atoms of magnesium,
approximately how many atoms of each isotope will be found?
Average Atomic Mass
7
Model 2 - NaturM Abundance information for Magnesium
Isotope
NaturMAbundance on Earth (%) AtomicMass(amu)
24Mg
78.99
23.9850
25Mg
10.00
24.9858
26Mg
11.0!
25.9826
7. Consider the natural abundance information given in Model 2.
a. Calculate the expected number of atoms of each isotope that will be found in a sample of 20
atoms of Mg. Hint: The number of atoms must be a whole number!
b, Is Model 1 accurate in its representation of magnesium at the atomic level? Explain,
8. If you could pick up a single atom of magnesium and put it on a balance, the mass of that atom
would most likely be __ ainu. Explain your reasoning.
9. Refer to a periodic table and find the box for magnesium.
a. Write down the decimal number shown in that box.
b. Does the decimal number shown on the periodic table for magnesium match any of the
atomic masses listed in Model 2?
The periodic table does not show the atomic mass of every isotope for an element.
a. Explain why this would be an impractical goal for the periodic table.
b. Is it important to the average scientist to have information about a particular isotope of an
element? Explain.
11. What would be a practical way of showing the mass of magnesium atoms on the periodic table
given that most elements occur as a mixture of isotopes?
12. Propose a possible way to calculate the average atomic mass of 100 magnesium atoms. Your
answer may include a mathematical equation, but it is not required.
POGILTM Activities for High School Chemistry
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Model 3 - Proposed Average Atomic Mass Calculations
Mary's Method
(78.99)(23.9850 amu) + (10.00)(24.9858 amu) + (ll.01)(25.9826amu)
100
Jack's Method
(0.7899)(23.9850amu) + (0.1000)(24.9858 amu) + (0.1101)(25.9826amu) =
Alan's Method
23.9850 amu + 24.9858 amu + 25.9826 amu
3
Complete the three proposed calculations for the average atomic mass of magnesium in Model 3.
Consider the calculations in Model 3.
a. Which methods shown in Model 3 give an answer for average atomic mass that matches the
mass of magnesium on the periodic table?
b. Explain why the mathematical reasoning was incorrect for any method(s) in Model 3 that did
not give the correct answer for average atomic mass (the one on the periodic table).
c. For the methods in Model 3 that gave the correct answer for average atomic mass, show that
they are mathematically equivalent methods.
15. Use one of the methods in Model 3 that gave the correct answer for average atomic mass to
calculate the average atomic mass for oxygen. Isotope information is provided below. Show all of
'our work and check your answer against the mass listed on the periodic table.
Isotope
160
NaturalAbundance on Earth (%) Atomic Mass (amu)
99.76
15.9949
170
0.04
16.9991
180
0.20
17.9992
Average Atomic Mass
9
Read This!
Recall that all isotopes of an element have the same physical and chemical properties, with the exception
of atomic mass (and for unstable isotopes, radioactivity). Therefore, the periodic table lists a weighted
average atomic mass for each element. In order to calculate this quantity, the natural abundance and
atomic mass of each isotope must be provided.
Consider the individual atomic masses for magnesium isotopes given in Model 2.
a. Which isotope has an atomic mass closest to the average atomic mass listed on the periodic
table?
b. Give a mathematical reason for your answer to part a.
17. Boron has two naturally occurring isotopes: boron-10 and boron-11. Which isotope is more
abundant on Earth? Use grammatically correct sentences to explain how your group determined
the answer.
POGILTM Activities for High School Chemistry
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Name
Period
ISOTOPES Worksheet
Name
Symbol
Atomic #
Mass #
# ofp
#ofn
# ofe
krypton-84
36
5O
hydrogen - 1
1
2
3
64
116
58
48
48
28
nickel-60
198
78
78
116
28
14
silicon - 30
uranium-235
238
92
11
1) Boron has two isotopes: boron-lO and borono11. Which is more abundant in nature?
2) Calculate the average atomic mass of magnesium. The three magnesium isotopes have
atomic masses and relative abundances of 23.985 ainu (78,99%), 24,986 amu
(10.00%), and 25,982 amu (11.01%)
3) Titanium has 5 isotopes as shown below. Calculate the average atomic mass of titanium.
Isotope
TI-46
TF47
Ti-48
Ti-49
Ti-50
Mass (am.)
45.953
46.952
47.948
48.948
49,945
%Abundance
8,00
7.30
73.80
5.50
5.40
4) A certain element exists as three natural isotopes as shown in the table below.
a) Calculate the average atomic mass of this element.
b) Write isotope notation (2 ways) for the most common isotope of this element.
Isotope
1
Mass(amu)
19,99244
Percent natural
abundance
90,51
Mass number
20
2
20,99395
0,27
2!
3
21,99138
9,22
22
5) Nitrogen has 2 isotopes: nitrogen-14 (14.003 ainu) and nitrogen-15 (15.000 amu). What
is the percent abundance of nitrogen=14 in nature?
12
Name:
Period:
Alpha and Beta Decay Reactions Practice
Write a balanced equation for each of the following nuclear reactions.
Example
Chlorine°36 decays by beta emission, Dubniumo262 decays by alpha emission
36
36
0
17 CI-4 18 Ar+_l e
262ÿ-.--
258-- +4He
105 L)O-'-ÿ 103 LF
1. Krypton-87 decays by beta emission.
2. Curium-240 decays by alpha emission,
3. Uranium-232 decays by alpha emission.
4. Silicon-32 decays by beta emission.
5. Zinc-7 ! decays by beta emission.
6. Americium-243 decays by alpha emission.
7, Cobalt-60 decays by beta emission,
8. Phosphorus-32 decays by beta emission.
9. Gadolinium-150 decays by alpha emission.
10, Lead-210 decays by emitting both a beta and an alpha particle.
13
Name
Per.
Half-life Worksheet
Fill in the missing information; show work below using either the formula or the chart method, Time units in first 2 columns must
matehl Convert when neeessary.
Half-life
90 min,
Elapsed time
6 hours
2,
300 years
600 years
27,6 g
3,
1 year
1 year
5246 g
,
235 years
705 years
20 g
,
35 years
140 years
lOg
7 years
49 years
lg
,
6,
Init amount Aÿ .ÿm0unt remaining
3000 mg
,
800 years
1600 g
100 g
,
8 billion years
1000 g
250 g
2 hours
5820 g
2910 g
9ÿ
10,
18 hours
3 days
500 g
11,
5 min,
30 min,
640 g
12,
2000 years
6000 years
8000 g
Show ÿour work!
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