Pennium
A Yakima WATERS 5E Lesson
Pennium Lab
Understanding the periodic table is a very important skill for beginning chemists. Atomic mass,
number of protons, neutrons, and electrons are the foundation for the structure of the periodic
table. For this exercise, students will be using pennies as a model of the element (Pennium). In
1982, the United States changed the composition of the penny changing it from pure copper to a
zinc center with copper plating. Because all of the pennies look the same, but have a different
weight they make a great model of the chemical isotope. Also, a demonstration will be used at
the end of the lab to show the students that the pennies are actually made from different
materials. This lab is intended for chemistry students in grades 10-12.
Standards
Science standards
9-12 APPD -The ability to solve problems is greatly enhanced by use of mathematics and
information technologies.
9-11 PS2B - Atoms of the same element have the same number of protons. The number and
arrangement of electrons determines how the atom interacts with other atoms to form molecules
and ionic crystals.
9-11 PS2J - The number of neutrons in the nucleus of an atom determines the isotope of the
element. Radioactive isotopes are unstable and emit particles and/or radiation. Though the timing
of a single nuclear decay is unpredictable, a large group of nuclei decay at a predictable rate,
making it possible to estimate the age of materials that contain radioactive isotopes.
Math standards
A1.8.A - Analyze a problem situation and represent it mathematically.
A1.8.C - Evaluate a solution for reasonableness, verify its accuracy, and interpret it in the
context of the original problem.
A1.3B. - Represent a function with a symbolic expression, as a graph, in a table, and using
words, and make connections among these representations.
A1.8.G - Synthesize information to draw conclusions and evaluate the arguments and
conclusions of others.
Outcomes
Upon completion of this exercise, students should be able to determine number of protons,
neutrons, and electrons for a given element. This relationship should then be used to define
isotopes and describe how they are formed and list some applications. Students should be able to
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calculate the average atomic masses of elements. They will also have practiced rounding
numbers and analyzing data.
Materials and Equipment
Students should be placed in groups (2 per group), or could work individually. Each group will
need a balance (preferably centigram), a plastic bag with twenty pennies inside, and a calculator.
Inside the plastic bags, place twenty pennies of varying dates. It’s important to have about ten
pennies from before 1982 and ten pennies from after. Also, you want to make sure the pennies
are fairly clean by removing any debris on the surfaces as this will change the weight.
For the demonstration done by the instructor: a Bunsen burner, striker, forceps, two pennies (one
prior 1982 and one after).
Prior Knowledge
Students should have prior knowledge of protons, neutrons, and electrons and be able to
determine the number for a given element (or atom). Some basic algebra skills are needed; such
as rounding, multiplication, division, and some simple manipulation of equations.
Safety
For this exercise, there aren’t any major safety concerns. The only portion that could potentially
be hazardous is done by the instructor. As for minor safety concerns, remind students to wash
their hands when finished.
Engage (10 min)
To engage the students, a question-lead discussion for a couple of minutes on topic of the
periodic table serves as a good review. Next a brief demonstration of why two pennies can have
different masses. To do this, simply take a penny older than 1982 and a penny that is newer than
1982 and weigh them. It’s best if this can be shown through a document camera on the overhead
projector. Then pass the pennies around and ask the students to hypothesize why they think the
masses are different. Remind them that they are both pennies!
Explore (15 min)
Students will get into groups of two, each with their own lab, and be given a station with a
balance, bag of twenty pennies, and a calculator (they should provide their own). Once at their
lab stations, they will complete the table in the Observations section of the lab. This section
requires them to record the date and mass of the pennies. They will also be asked to round the
recorded masses from the hundredth place to the tenth place. This step serves as a good review,
but is also very important for the correct completion of the lab.
The calculations portion of the lab guides the students to understand that there is a different in
the masses of pennies. They should mainly see two different mass categories after rounding their
numbers; one should be about 3.1g which is from the pre-1982 pennies, and the other will be
about 2.5g for the post-1982 pennies.
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Explain (15 min)
The explanation portion of the exercise comes in the application section of the lab. This is where
the students read a brief application which helps them relate pennies to isotopes. The goal is to
get them to understand that the pennies were being used a model. Then they will be asked to
explain the extended knowledge. How many isotopes did they have? How do they know?
It is also a good idea to directly (verbally) ask the students what did the pennies symbolizes,
especially if they’re not making the connection between the pennies with isotopes. This is a
good way to ensure that all the students have made to proper connections; however, you want to
do this toward the end. Give the students the opportunity to make the connection on their own.
Extend (15 min)
Toward the end of the lab, the students are asked to give a couple examples of isotopes and how
they are used. During the demonstration, students will need to use the information they have
learned to describe what’s taking place.
Evaluate (20 min)
Students will be evaluated based on their responses from their lab using the following rubric.
Also questions on the exam related to calculating average masses and explaining isotopes will be
used.
Performance Rubric
Element
Great (5)
Good (4)
Conceptual
Understanding
(35%)
Application
questions:
1,5,6,7, demo
Student shows
a solid
understanding
of the content
by being able
to describe and
apply the
information
covered and be
able to connect
all the concepts
included
Student will
have a solid
understanding
of the content,
but are having
some trouble
making all the
connections
Skill 1 (15%)
(simple
mathematical
skills) PA
questions: 1,2
Students were
able to
properly
perform the
necessary
mathematical
equations and
calculated
them correctly
Students were
able to
properly set up
all the
necessary
equations,
some error in
calculating
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In
Development
(3)
Students
understand
some of the
content but
were unable to
make most of
the
connections
Needs
Rethinking (2)
Poor (1)
Students had
little to no
understanding
of the content
and were
unable to make
valid
connections
Students had
no
understanding
of the content
and did not
attempt to
make any
connections
Students made
a few errors in
setting up
mathematical
equations, but
calculated
them correctly
Students were
unable to set
up
mathematical
equations, but
calculated
them correctly
Students were
unable to set
up
mathematical
equations and
unable to
perform
calculations
Skill 2 (25%)
(Making a table
and
understanding
data) Data
table, PA
questions:1,2,3
and App
question: 3
Skill 3 (25%)
(Calculations
involving
average mass
and percent
abundance)
Application
questions:
2,3,4,5
Students were
able to
properly fill
table, and were
able to extract
data and
explain it
completely
Students made
a simple
mistake filling
in table, but
were able to
explain their
results properly
Students made
no mistakes
filling in table,
but had
problems
explaining
their results
properly
Students made
mistakes filling
in table and
had trouble
explaining
their results
Students could
not/would not
fill in data
table and
couldn’t
explain
Students were
able to
properly carry
out
calculations,
figure out
percent
abundance, and
explain
significance
Students made
simple errors
in calculations,
but were able
to explain
significance
Students made
simple errors
in calculations,
and were
unable to
explain
significance
completely
Students made
major errors in
calculations,
and were
unable to
explain
significance
completely
Students did
not do the
calculations,
and did not
explain
significance of
them
Teacher Background Information
Understanding the atomic composition of an element is imperative in composing a solid
foundational understanding of chemistry. The number of protons is given in the periodic table
(which is the atomic number). The number of electrons can be figured out by subtracting the
charge of the given element by the number of protons. An example is P3-: by looking on the
periodic table of elements you can figure the number of protons to be 15 (atomic number). To
figure out the number of electrons you take 15-(-3) which equals 18 electrons. Neutrons can be
factored in when you have the atomic mass given. The average atomic mass subtracting the
number of protons will give you the number of neutrons. All the isotopes of an element are
factored into the average atomic mass based on their percent abundance. An isotope looks like a
normal element (or atom), however, its mass is different because it contains a different number
of neutrons.
Resources
The instructions for the demonstration were obtained from Mr. James Klarich from Davis High
School.

Using a Bunsen burner, hold a pre-1982 penny with forceps in the flame for a couple
minutes. Because the penny is made of pure copper it will glow a hot red color. It’s best if
you turn the lights off so the students can see the color better. Then do the same thing with a
post-1982 penny. Because the penny is only copper plated, it will melt and the zinc inside
will spill out onto the counter. This is best seen with the lights on.
http://www.chem4kids.com/files/atom_isotopes.html, www.youtube.com/watch?v=Jdtt3LsodAQ
By: John (Eric) Inions, Fall 2011, for Davis High School
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Pennium Lab
Name:____________________
Procedure
1.
2.
3.
Each group needs a resealable bag full of pennies. Remove the pennies and count them to make sure
that there are 20. Determine and record the combined mass of your 20 pennies.
Find the mass of each penny separately. In the Data Table, record the year the penny was minted and
its mass to the nearest 0.02 grams.
When finished place the 20 pennies in the resealable bag and return the pennies and the laboratory
balance to the area designated by your teacher. Return to your seat and finish the pre-application
calculations.
Observations
Penny
DATA TABLE
Year
Mass (g)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
5
20
Pre-application Calculations
1. What is the combined mass (to nearest 0.05 g) of 20 pennies? _____________
2. Is the mass of 20 pennies equal to 20 times the mass of one penny? Explain.
3. Rounding to the nearest 0.05, how many different weights are there in your data table from
above?
Application
Unless you’re a coin collector, you probably think all the United States pennies are pretty much
the same. To the casual observer, all the pennies in circulation do seem to be identical in size, thickness,
and composition. But just as elements have one or more isotopes with different masses, the pennies in
circulation have different masses. For this application, use the data from before of the pennies with
different masses to represent different “isotopes” of an imaginary element called pennium, or Pe.
Remember that chemical isotopes are atoms that have the same number of proton, but different number of
electrons. Thus, chemical isotopes have nearly identical chemical properties, but some different physical
properties.
For application purposes, you will determine the relative abundance of the isotopes of pennium
and the masses of each isotope. You will then use this information to determine the atomic mass of
pennium. Recall that the atomic mass of an element is the weighted average of the masses of the isotopes
of the element. This average is based on both the mass and the relative abundance of each isotope as it
occurs in nature.
Questions
1. Record the number of isotopes of Pe based on your answer in number three from above.
2. Calculate the percentage of each isotope present out of the 20 pennies. This is also called
Percent Abundance. (Remember it should add up to 100%) Also record this number as a
decimal (divide by 100).
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3. Calculate the average mass of each of the isotopes.
4. Calculate the average atomic mass of each isotope.
Use this equation:[ (atomic weight of isotope from #3) X (% abundance(decimal from question #2))] +
[(atomic weight of isotope from #3) X (% abundance(decimal from question #2))]
5. How can you explain the fact that there are different “isotopes” of pennium?
6. List at least three examples of how isotopes are used in the world?
7. Describe what the pennies were used for today? What did they represent?
Demo
For this portion of the lab, your instructor will conduct a demonstration.
Describe what is happening and explain (using words from the chapter of your textbook).
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