Sticky Tape Discussion SB

Sticky Tape Lab
Discussion
Chemistry-Unit 6: Particles with Internal
Structure
Lab Debriefing
Develop a class consensus table of results
Learning Targets
Learning Targets
Describe evidence that
supports the idea that
particles have a property
called “charge”.
Synthesize observations
into a logical pattern of
behavior demonstrated
by the various strips in
the lab.
Assessments
1. 
Conclusion to lab
2. 
Conclusion to lab
Charge?
"  
Which of the items do you believe had a
charge?
"  
"  
Why do you believe this?
Two tapes - demonstrated attraction and
repulsion
Not charged?
"  
Were there any items that did not have a
charge?
"  
"  
Why do you believe this?
Paper and Foil - while they were
attracted to both tapes, they were not
attracted to themselves or each other
Neutral?
"  
If the Paper and Foil are neutral, how could
they have been attracted to both the
positive and negative tape?
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What does neutral really mean?
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No charge?
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Equal amounts of positive and negative
charge
Transfer?
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What is the smallest thing we are aware of
that could be transferred?
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Atoms
Does moving an atom or group of atoms from
one place to another change the charge of
something?
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No - therefore ** there must be
something smaller than an atom that was
transferred
Timing
"  
When did the tape become charged?
"  
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After we ripped them apart.
If they didn’t become charged until we
ripped them apart, what conclusion can we
draw?
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** There was something transferred
during the ripping
Something smaller?
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Based on our observations so far, what
characteristics can we assign to this object?
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It’s smaller than an atom
It’s mobile (it moved from one tape to
another)
It has a charge (moving it changed the
charge of both tapes)
Which charge?
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If it’s charged, is it positive or negative?
"  
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If it’s positive, it moved from the bottom
tape to the top tape, increasing the +
charge of T and decreasing the + charge
of B
If it’s negative, it moved from the top
tape to the bottom tape, increasing the charge of B and decreasing the - charge
of T
Begin Your Conclusion
1. 
Describe your evidence that
supports the idea that particles
have a property called “charge”.
New Model
 
 
J.J. Thomson came up with a new model of an
atom to incorporate this tiny negative particle
that we call electrons.
The black dots represent the electrons, which
called plums. These are negative. The rest of
the atom was like a bowl of pudding. The bowl
pudding is positive
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This model is called the Plum Pudding Model
the Atom
Evidence for Thomson’s Model
• 
Cathode ray was bent by a magnetic field
• 
• 
Cathode ray was bent by an electric field toward the
positive pole.
• 
• 
Conclusion: The “ray” must be negative.
Didn’t matter what kind of metal was used to generate
the cathode ray.
• 
• 
Conclusion: the “ray” must be matter with
electromagnetic properties
Conclusion: can be generated by any element
Measured charge-to-mass ratio
• 
Conclusion: mass is ~1/2000 the mass of a H atom
w what do we know about the cause beh
e attractions & repulsions observed in la
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It’s smaller than an atom
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It’s mobile
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It has a charge
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That charge is negative
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What do we call this??
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Electron
Transfer?
So, the plums (electrons) transferred from the
pudding (atom) of the top tape to the bottom ta
o, the bottom tape is “plum rich” and the top tape
“plum poor”
Complete your own diagram of these atoms & tape
in your notebook)
Conclusion Question #2
escribe the macroscopic changes in the
pes,
d then provide a microscopic explanation
ased upon Thomson’s model of the atom a
ur drawings.
Foil & Paper
Foil (metal atoms) was not attracted or
repelled by foil.
Paper (non-metal atoms) was not attracted or
repelled by paper.
**BUT…both were attracted to both Top &
Bottom Tape!
How can we use the plum pudding model of
atoms to explain the differences we observed?
Neutral
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objects?
Can this model explain how a neutral object
can be attracted to both positive and
negative?
his is a good model of what occurs in the paper.
The pudding is “sticky” in non-metals. The electro
an move in the bowls but not out of the bowls.)
olarization: when a charged object redistributes
We still have one question t
 
answer...
Why was the foil more attracted to the
charged objects than the paper was?
from Atom to Atom
• 
• 
• 
In neutral foil, electro
are equally distributed
between atoms &
homogeneously dispers
within each atom
In metals, bowls of
pudding are really “so
& electron “plums” ea
move from bowl to bow
The positively charged
tape has polarized the
foil---Why?
top tape. (Be sure the size of the vect
ws the relative strength of the
ractions)
raw electrons in each atom “bowl” for th
per
tape. (Be sure the size of the vectors
ws the relative strength of the
ractions)
aw electrons in each atom “bowl” for th
Conclusion Questions #4 & #5
Explain why these previous 2 arrangement
electrons would produce the observed
attractions (between paper & tape & betw
foil & tape), but no attraction of either st
to one just like it (paper to paper; foil to
foil).
Why was the foil more attracted to the
charged objects than the paper was?