Mystery: Structure of the Atom - A Case for Indirect Evidence

Miriam Meade Saint Joseph School
17949 Dixie Hwy.
Homewood IL 60430


To acquaint Junior High students with the history, through indirect evidence, of
the discovery of each component of the atom with hands on simulation activities.

Materials needed:

4 boxes (sealed) labeled Box X with approx. 4 Electroscopes constructed of
10-15 items i.e. ball, knife, lid, pen 2 film canisters each with
4 elevated (tablelike) pieces of Plexiglass, 2 straws stuck into the
dry rice grains, bits of styrofoam, puffed canisters as if antenna
rice, wool scarf 4 boxes, Mystery Box Y, with
2 large clay balls; one with a small rubber concentric circles forming
ball inside, the other, a large marble paths with a definite # of
4 boxes, Mystery Box Z, with elliptical paths marbles per path
and a definite # of marbles per path Large plastic eggs with a
hollow ball inside filled
with candy representing the
subatomic particles
I. Invisible Phenomena:
A. Indirect evidence
Activity I - Objective: To demonstrate the behavior of matter by indirect
1. fan blowing across hidden wind chimes and open perfume bottle
2. cold glass of water - no ice - condensation
3. 2 dishes of water, one in the sun - evaporation
Activity II - Objective: Mystery Box X can simulate, through indirect
evidence, how we can learn about the structure of the atom.
1. distribute sealed Box X filled with about 10 items of various sizes etc.
2. using Scientific Method, determine what is in box (how?
3. group records observations, conclusions - report to class
4. in discussion, bring up the term "model"
5. using the word 'model', start Words to Know list (See I B)
Activity III - Electroscope - Objective: to demonstrate that atomic particles,
invisible yet must exist, can move or be torn away
1. each group receives 2 film canisters with 2 bent straws adhered to bottom
of canister with clay; set them about 6 inches apart
2. tear 2 four inch pieces of transparent tape, press them onto a hard
surface allowing a short amount unattached to use as handles
3. quickly tear the tape from the surface and attach to one straw of one
canister, repeat for the other piece of tape but on other canister straw
4. move canisters closer - watching for reaction of the 2 pieces of tape
(should repel each other)
5. take 2 more pieces of four inch tape; place the sticky side on the smooth
side of piece 2, again leaving enough unattached to use as handles
6. tear tape away quickly; attach to 2 remaining straws, watch for reactions
as canisters are moved forward etc. (should attract each other)
7. run a comb through hair & direct inbetween tapes for additional reactions

Activity IV - Dancing Rice & Circus Fleas - Objective: (same as for Act. III)
1. an elevated piece of Plexiglas (table style - about 8-12 in.sq.) is
placed on the desk
2. bits of styrofoam, dry rice grains, or puffed rice are placed under the
3. rub the surface with a wool cloth creating "static electricity"
4. observe action/reaction of objects under the Plexiglas
5. in groups, report your observations - specifically in terms of what is
happening and why
6. in groups, answer the following questions about Act. I through Act. IV:
a. what is the correlation between Act. I and Act. II; correlation
between Act. III and Act. IV: and the correlation between all four
b. do these activities have a relationship to the "invisible particles"
we're trying to learn about?

B. Words to Know
1. List all pertinent words, derivation, and definition (ie. atomos, Greek
cannot be divided) as they are introduced in Models of the Atom
2. List should include: model electron nucleus atom proton
neutron atomic particles
II Models of the Atom
Activity V - Objective: to give background information of the discovery of the
subatomic particles, with students, given pertinent information,
role-playing each scientist
A. Democritus - believed that atom was a solid and indivisible
B. Dalton - believed it was a solid, indivisible, with different atoms for
different elements
C. Thomson - discovered electrons (negative charges) but believed they were mixed
with positive charges (given name protons) throughout atom in a
"plum pudding" idea (chocolate chip idea too)
D. Rutherford - proved positive particles existed (gold foil experiment) but
were held in a central core which he called "nucleus"
E. Chadwick - discovered neutrons existed with the protons in the nucleus
F. Bohr - believed that the nucleus, made of protons and neutrons, had the
greatest mass; electrons were located outside the nucleus traveling
in paths called energy levels
G. Schrodinger - Electron Cloud Theory - basic difference being that the
electrons are found in "probable" locations outside the nucleus on
energy levels and that the atom is mostly empty space

III Recap of Ideas
Activity VI - (mini-assessment) Table to be filled in is provided covering:
particle name and charges, location in atom and approximate size.
Activity VII - Brainstorm: in groups - Based on your present knowledge as a
scientist, discuss the following:
1. What questions about the atom do you think still need to be
answered? List them.
2. Why would it be important to know?
3. Record and report.
Activity VIII - Objective: To recognize the two current models of the atom being
used: The Bohr and Electron Cloud Models.
1. 2 boxes labeled Y and Z are distributed to each group.
2. As with Box X, the Scientific Method (SM) is used to gather indirect
evidence on the behavior of the objects in each box, paying particular
attention to the movement.
3. record and report by group
4. open Box Y - decide which atomic model it represents; one person in group
draws the model on the board
5. open Box Z - repeat as in step four
6. list similarities and differences on the board
Activity IX - Edible Subatomic Particles - Objective: To review what has been
learned so far about the two working models of the atom.
1. a large plastic egg is given, one per person - each egg contains a split
ping pong ball (nucleus) with a set # of gumballs and candy (neutrons and
protons) inside; an equal number of hard candy moves freely around the
ping pong ball (electrons)
2. using the SM again determine the components within as to number, size,
movement, weight/mass, sound
3. open eggs - now report on the contents specifically as to number and size
only. What are their correlations? Discuss.
4. eat contents while taking the Final Performance Assessment
Activity X - Brainstorm: Objective: To present new ideas that may be continued
in the text or through class presentation
1. Where and how to search for new information
2. Relationship to Astronomy
3. Practical application of atomic knowledge
4. quarks atomic numbers isotopes photons
ions Periodic Table

IV Final Performance Assessment:
Your school is being visited by a delegation of top scientists from three
technologically rich countries: Japan, Germany, and Canada. One of the purposes
of their visit is to determine whether U.S. junior high students have a full
grasp of the Atomic Theory before extending an invitation to them to apply for a
summer job working with the World Atomic Energy Commission.
To demonstrate your abilities in this field, you are to do the following:
A. With the materials provided: thumbtacks of 3 different colors, paper and
1. choose one of the elements given on the board to use as your example for
the two models to be drawn
2. draw and label all parts of the Bohr model and Electron Cloud model of
the atom, using the tacks to represent the subatomic particles
3. indicate the charges of each particle
B. Design an experiment that would prove the existence of subatomic particles.
Include everything you know about the atomic theory.
1. Explanation may be given in paragraph form (include how and why)
2. Diagrams may be used
3. If futuristic technology is included, functions must be specifically
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