Modeling Metals with Marbles & BBs (Lesson Plan)
(Kinetic particulate nature of matter and the Electron Sea Model)
Suggested Grade Level
9-12
Standard Statements
3.1.10 B Describe concepts of models as a way to predict and understand science and
technology.
3.4.10 A Explain concepts about the structure and properties of matter.
3.4.12 A Apply concepts about the structure and properties of matter.
Content Objectives
Students will know that
1. Metal atoms in the solid phase are very ordered, closely packed, and held in fixed positions.
2. It often requires extreme temperatures to both melt and vaporize metals.
3. The electron sea model depicts metals as a lattice of cations surrounded by a mobile sea of
valence electrons.
Process Objectives
Students will be able to
1. Model the metal atoms in the solid, liquid, and gas phases using marbles and Petri dishes.
2. Model the mobile sea of valence electrons using BBs.
Assessment Strategies
1. Evaluation of completed student handout.
2. Group discussion of key ideas.
3. Evaluation of a reflective essay describing what they did during the activity, what they feel
they learned, what aspects of the lesson they feel they still do not understand, and one
question that they are curious about regarding metals.
Materials
Per group or per individual:
 3 Petri dishes (at least one should be a square Petri dish)
 44 (12 mm size) marbles
 40 BBs (shot-gun shell shot will also work)
 Tape or polystyrene glue to seal Petri dishes
Procedures
Part 1
(20 min)
1. Distribute all materials to each group or individual.
2. Students place 40 marbles in the square Petri dish, 3-4 marbles in another Petri dish, and
~40 BBs in the remaining dish. Each dish (especially the one containing the BBs) should be
taped or glued shut.
3. Explain that in this activity the marbles in the Petri dishes will represent metal atoms, and
the BBs will be used to represent electrons in a metal.
4. Students hold the square Petri dish on a slight tilt so that all the marbles congregate toward
one side and are in a closely packed arrangement. While still holding it on a tilt, they gently
Modeling Metals with Marbles & BBs
Lesson Plan
1
5.
6.
7.
8.
shake the dish and notice that for the most part, the marbles stay fixed in their original
positions. The students sketch a picture of how the marbles look in this configuration and
provide a brief written explanation of what they see.
Students vigorously shake the square Petri dish to observe the marbles come out of their
fixed positions. They illustrate and describe what they see.
Students observe the behavior of the 3-4 marbles in the second Petri dish as they shake it
vigorously. They sketch a picture and describe what they see.
The students predict which of the three tasks models metal atoms in each of the three phases
(solid, liquid, or gas). They compare the melting and boiling points of water to the extreme
temperatures required to melt and boil various metals from the Periodic Table.
Discuss key ideas about metal atoms in the solid, liquid, and gas phases (see Teacher Notes).
Part 2
(30 min)
1. Discuss the electron sea model of metals with the class before the students attempt to model
it using the BBs (key concepts of this model are included in the Teacher Notes).
2. Students place the Petri dish with the BBs over top of the diagram in their student handout
which depicts a collection of positively charged point particles in fixed positions. The
students move the Petri dish back and forth over top of the diagram and record what they
observe. They provide a written explanation of how this task illustrates the electron sea
model of metal atoms.
3. Emphasize key components of the electron sea model in light of the visual representation the
students now have. Point out that the mobile nature of electrons depicted in this model is
useful in explaining many properties of metals (conductivity, ductility, malleability, etc.).
Modeling Metals with Marbles & BBs
Lesson Plan
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Modeling Metals with Marbles and BBs (Teacher Notes)
(Kinetic particulate nature of matter and the Electron Sea Model)
General Lesson Notes

Configurations of Petri dishes. Configurations of the Petri dishes should similar to the
diagrams below.

Distinction between marbles and BBs. Make sure the students understand that the marbles
represent metal atoms and the BBs represent electrons.

Distinction between Part 1 and Part 2. The first part of the activity deals with the kinetic
particulate nature of matter (specifically, what happens to the atoms in a metal as heat energy is
provided), and the second part attempts to illustrate the electron sea model of metals.
Atoms in a metal in the solid phase
Atoms in a metal in the gas phase
Atoms in a metal in the liquid phase
Mobile “sea of electrons”

Properties of Metals:
Malleability. Malleability is a property of metals that allows them to be bent or flattened
without breaking. This property is possible because metallic nuclei can slide past one
another into new positions without breaking the ionic bonds that hold the solid together.
The bonds do not break because the atom’s valence electrons move with the nuclei as the
nuclei are repositioned.
Electrical Conductivity.
Thermal conductivity. As a metal is heated, thermal energy is transferred to the electrons
in the valence shells of the metal atoms causing them to move at a faster rate (i.e. gain more
kinetic energy). This is why metal objects get hot quickly.
Modeling Metals with Marbles & BBs
Teacher Notes
1
Metallic Luster. The atoms of a solid are packed closely together such that their outer-most
valence shells overlap. Ideally, if the individual valence atomic orbitals overlapped, all of
the valence electrons would be in one large orbital of a single energy. Paulii’s Exclusion
Principle states that no more than two electrons can occupy the same orbitial; therefore, the
valence shells of the atoms packed into a metallic solid split into many different energy
levels. Due to this fact, every wavelength of the visible spectrum (and electromagnetic
radiation outside of the visible range) can be absorbed by a metal. The metal absorbs
photons, the electrons are excited to higher energy levels and then relax back to their
original states thereby releasing energy in the form of visible light. If all of the visible light
is thereafter reflected the metal appears silver. If some of the blue and violet light is
permanently absorbed it appears gold or copper.1
Part 1 Notes

Metal atoms in the solid phase. (This explanation pertains to Question 2a in the Student
Handout.) Metal atoms in the solid phase are arranged in very ordered and compact patterns.
There are several arrangements in nature that allow for very close packing (body-centered cubic,
face-centered cubic, hexagonal close-packed, etc). A discussion of these arrangements is not
necessary for doing this lesson (but would definitely be relevant if desired). Rather, it is only
needful that students understand that atoms of a metal adopt very ordered, geometric
arrangements in the solid phase to pack themselves as close together as possible. By using
square Petri dishes to model atoms in the solid phase, it is hoped that students will be able to see
this.

Metal atoms in the liquid phase. (This explanation pertains to Question 2a in the Student
Handout.) Metal atoms in the liquid phase have more energy than atoms in the solid phase.
Emphasize that many common metals require very high temperatures to be melted (reach their
liquid phases).

Metal atoms in the gas phase. (This explanation pertains to Question 4a in the Student
Handout.) It is clear from the boiling points in Table 1 that it takes an even greater amount of
energy to get a molten metal to boil (for metal atoms to enter the gas phase). At such extreme
temperatures, there is often enough energy for metal atoms to ionize (loose electrons).
Although there is in fact a vapor pressure above molten metals, it is extremely low (the density
of the vapor is nearly miniscule). The very few metal atoms existing in the gas phase have the
most the most mobility (and greatest kinetic energy), which should be evident from having only
three or four marbles moving around in the second Petri dish.

Melting and Boiling Points of Metals. (This explanation pertains to Question 2c in the Student
Handout.) Table 1 is a list of selected elemental metals and their respective melting and boiling
points. It may be useful to have the students convert a few of the temperatures into °F, since it
is with this temperature scale that the students are most familiar.) Since metal atoms will have
much more energy in the liquid phase, they have greater mobility (greater kinetic energy) than
metal atoms in the solid phase.
1
http://einstein.byu.edu/~masong/HTMstuff/textbookpdf/C20.pdf
Modeling Metals with Marbles & BBs
Teacher Notes
2
Table 1. Metals and their melting and boiling points in oC.*
Metal
Melting Point (oC) Boiling Point (oC)
Chromium 1907
2671
Platinum
1768
3825
Iron
1538
2861
Nickel
1455
2913
Copper
1085
2562
Gold
1064
2856
Silver
962
2162
Aluminum 660
2519
Magnesium 650
1090
Zinc
419
907
Lead
328
1749
Cadmium
321
767
Tin
232
2602
*
Lide, D.R. (Ed.). (1996). CRC Handbook of Chemistry and Physics, 77th Edition. CRC Press.
Part 2 Notes

Electron Sea Model. (This explanation pertains to Questions 3a through 3c in the Student
Handout.) The electron sea model of metals involves the notion that atoms in a metal do not
hold onto their valence electrons very tightly, thus enabling them to share these valence
electrons with one another. Paulii’s Exclusion Principle states that no more than two electrons
can occupy the same orbitial; therefore, the valence shells of the atoms packed into a metallic
solid split into many different energy levels such that the valence electrons no longer belong to
one particular nucleus and each atom in a metal shares its valence electron(s), This essentially
creates a lattice of cations (positively charged atoms that have “given up” one or more electrons)
surrounded by a mobile “sea of electrons.” The cations are held in relatively fixed positions,
while the valence electrons are free to move and drift from one part of the metal to another. It is
hoped that by having the students move the dish containing the BBs over the 2-D picture of
positive point particles (provided in the Student Worksheet) that students will gain a visual of
what this model is depicting for metals. It should be emphasized to students that the BBs
represent one valence electron from each of the particles in the diagram. The attraction
between the mobile electrons (negatively charged) and the cations (positively charged) result in
the metallic bond which functions as the “glue” that holds metals together. The model of
electrons in a metal being very mobile is useful in explaining many of the properties of metals
that we observe (good conductors of electricity, ductility, malleability). For example, a sheet of
metal that is subjected to blows from a hammer will not shatter into pieces.
Notes on materials

Petri Dishes. Square Petri dishes (100 mm x 15 mm; disposable polystyrene) should be
available through a variety of distributors. They are used in the first part of this activity because
a better picture of close-packing in the solid phase emerges with a square dish instead of a round
one. One supplier (Science Kit® and Boreal® Laboratories) sells them for $6.75 for a package
of ten.
Modeling Metals with Marbles & BBs
Teacher Notes
3

Marbles. Marbles of 12mm diameter are smaller than typical, standard-size marbles you might
find in a store, and they are used in this activity so that the lid will fit over top of the Petri dish.
Smaller marbles (9-11 mm) can be used, but larger marbles should be avoided or else the dish
lids will not fit. Marbles with diameters of 9, 11, and 12 mm can be bought in bulk quantities
from an online distributor such as “megaglass.com” (URL as of January 2005 is
http://www.megaglass.com/) for as little as $3.33 for 175 pieces.
Modeling Metals with Marbles & BBs
Teacher Notes
4
Name:________________________
Modeling Metals with Marbles and BBs
(Kinetic particulate nature of matter and the Electron Sea Model)
Overview
In this activity, you will use marbles to represent the atoms in a metal and BBs to represent
electrons in the electron sea model. You will gain a visual representation of what happens on the
atomic level as metals are heated (kinetic particulate nature of matter) and also of how the electron
sea model depicts the bonding in metals.
Part 1 (Kinetic particulate nature of matter)
1) Place 40 marbles in the square Petri dish, and tape or glue it shut. Hold the dish on a slight tilt
so that all the marbles congregate toward one side and are in a closely packed arrangement. While
still holding the dish on a tilt, very gently shake the dish back and forth, and observe how the
marbles behave.
a) Sketch a picture of how the marbles look, and briefly explain in words what you see.
b) Now vigorously shake the square Petri dish, and observe how the marbles behave. Sketch
picture that approximates what you see, and explain in words what was different from what
you saw in question 1a.
Modeling Metals with Marbles & BBs
Penn State University GREATT Project
Student Handout
1
c) Place 3-4 marbles in a second Petri dish, and move it back and forth somewhat vigorously.
Draw and explain what you observe
2) Think about the three tasks you completed in Part 1. Answer the following questions:
a) The marbles in each of the tasks in Part 1 represent atoms in either the solid, liquid, or gas
phase. Which task represents which phase? Why?
b) Based on your observations, what can you say about what happens as atoms are heated and
gain energy?
c) Refer to Table 1 in the Additional Resources section. If solid ice first begins to melt (enters
the liquid phase) at 0°C, and pure liquid water boils (enters the vapor phase) at 100°C, what
can you say about the temperatures required to melt and boil metals?
Part 2 (Electron Sea Model)
3) After your teacher has discussed the electron sea model of metals, proceed onto item 3a.
a) Place 40 BBs in a third Petri dish, and glue or tape it shut. Place this Petri dish over top of
diagram provided (Figure 1), and move the dish back and forth as you keep it flat on the
table or desk. Record your observations, and describe how this simulates the electron sea
model of metals as discussed by your teacher.
Modeling Metals with Marbles & BBs
Penn State University GREATT Project
Student Handout
2
b) What do the BBs represent?
c) What do the circles in the diagram represent?
Figure 1. Diagram for Item #3a.
Modeling Metals with Marbles & BBs
Penn State University GREATT Project
Student Handout
3
Post-activity reflective essay
Write a few paragraphs describing what you did during this activity. Also address what you feel
you learned and what aspects of the lesson you feel do not understand. Include one question
regarding metals that you are curious about.
Modeling Metals with Marbles & BBs
Penn State University GREATT Project
Student Handout
4
Additional resources
Table 1. Metals and their melting and boiling points in oC.*
Metal
Melting Point (oC) Boiling Point (oC)
Chromium 1907
2671
Platinum
1768
3825
Iron
1538
2861
Nickel
1455
2913
Copper
1085
2562
Gold
1064
2856
Silver
962
2162
Aluminum 660
2519
Magnesium 650
1090
Zinc
419
907
Lead
328
1749
Cadmium
321
767
Tin
232
2602
*
Lide, D.R. (Ed.). (1996). CRC Handbook of Chemistry and Physics, 77th Edition. CRC Press.
Modeling Metals with Marbles & BBs
Penn State University GREATT Project
Student Handout
5