If we could see atoms, kids might …

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If we could see atoms,kids might …

Lynn A. MeltonUniversity of Texas at Dallas

[email protected] January 26, 2008

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Sequence of IdeasComments on Teaching*Fundamental Concepts of Chemistry*Chemistry Seems Arcane*ModelsDefinition of Atom*Data for atoms

Atomic Force Microscopy (AFM)Mass Spectroscopy (MS)

Hands OnAtoms* (Seeing Without Seeing)AFMMS

* = today

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Comments on Sequence

• Lots of ideas there

• It you use this material in the classroom, it may take you a month or more to work through the material.

• The “hands on” stuff will count as labs.

• No algebra! No exponents!

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Comments on Teaching

• What can the Coca-Cola Company tell us about teaching?– Advertisements are delivered to a passive

audience.

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audience.– “It takes 20 reps of an ad to start to move the

market.”

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audience.– “It takes 20 reps of an ad to start to move the

market.”– “It takes 8 reps for the audience to know that

the ad is running.”

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• What can the Coca-Cola Company tell us about teaching?– Concepts are delivered to a passive audience.– “It takes 20 reps of a concept to start to move

the minds.” ??– “It takes 8 reps for the students to know that the

concept is there.” ??

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Fundamental Concepts ofChemistry

• Atoms

• Bonding/Molecules/Reactions

• Structure/Properties– Activity of molecule derives from its structure

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Chemistry Seems Arcane

A conceptual chemistry problem:• Question: Does the blackened copper wire

weigh more, same, or less than when it was in the flame?”

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• A secondary school teacher was in the class, and came to me for help with this homework problem.

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• She could tell me that the flame cleaned the surface of the dirty copper wire and that oxygen from the air reacted with the clean surface to produce copper oxide, which is black.

• She went back and forth as to whether the weight was “more”, “same”, or “less”.

• She was guessing.

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• I tried to help. Knowing that she once had taught Home Economics, I said, “Go to the grocery store and fill a basket with oranges. Now put a layer of avocados on top of the oranges. Does the basket weigh more, same or less when I add the avocados?

• “Oh, Dr. Melton, of course it weighs more”.

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• She could reason well enough, but when she was asked about atoms, she turned off her reasoning. The atomic world seemed ARCANE.

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• The atomic world seemed ARCANE.– Known or understood by only a few: arcane

economic theories. – adj : requiring secret or mysterious knowledge;

"the arcane science of dowsing“– Definitions from dictionary.com

• In the arcane world, the normal rules do not work, and you might as well guess.

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• Would she have guessed if she could have seen atoms?

• Can your students see atoms?

• The atomic world seemed ARCANE.– In the arcane world, the normal rules do not

work, and you might as well guess.

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Atoms: Key Question• If a sassy eighth grader asked you “So why – other

than you and the book say so – should I accept that the world is granular? After all, I cannot see atoms.”

• Your answer has three parts:– Define an atom carefully– Data #1:Atomic Force Microscopy (the world is granular)– Data #2: Mass Spectrometry

(the particles have different weights)

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Atoms

• Definition of an atom (a la Melton)– Rip any piece of the world apart, but you may

use only the energies available to the ancients – horses, flames, and lightning. When you cannot rip the smaller pieces apart any longer [to produce only neutral particles] then those last [neutral] particles are ATOMS.

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AtomsDigression

• Words that may come up. (If they don’t ask, don’t bring them up; Keep to the simple model)– Electron, proton, neutron: subatomic particles, they will

be discussed as more complex MODELS– Element: a group of atoms all of which have the same

number of protons– Ion: a atom in which the number of electrons is not the

same as the number of protons– Isotopes: atoms that have the same number of protons

but different numbers of neutrons

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Atoms: Getting the Concept

• The weight of anything in the world is the same, regardless of how finely you divide it.

• Or, when you add up the weight of all the pieces, you get the weight of the original thing.

• The world is granular; it is– Sand rather than shampoo

– Grapes rather than jello

• Every material in the world is built from atoms.

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Let’s Work with Atoms

• This hands-on exercise is part of a series of lessons, all designed to help students accept that atoms are real.

• Since, atoms are too small for us to see with our eyes, let’s work on Seeing Without Seeing.

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AtomsSeeing Without Seeing

• What do we need to know about atoms?– What is your weight?– What can I build with you? (or, What other

atoms can you bond to?)

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• Each team must have an A and a B– A is the person with the gaudiest clothing

• In this exercise, A is the “doer” and B is the “recorder”.– A may not write– B may not touch.

• We will switch roles later.

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• A space probe has just returned from Planet Xanadu with samples of material.

• Your assignment is to go into the laboratory and find out whether the samples display the same chemistry that we observe on earth.

• In particular, on Planet Xanadu, is there a periodic table?

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• The garbage bag is your laboratory. It contains material from Planet Xanadu.

• One person inserts both hands into the garbage bag and does the research. The other person records the results.

• Please do not peek. At the right time, I will tell you when to look.

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• Carry out your research, write up the results, and make sure that A and B agree on what has been written.

• Switch bags with adjacent team.

• Check the results of the other team, but now A is the “recorder” and B is the “doer”.

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• Now, the whole group discusses their results.

• This is our version of an international scientific meeting.

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• Hands On Time!

• Go to it!

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• Switch bags with another team.

• Each team analyzes the other sample.

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• Now, all together, let’s discuss the results.

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• On Planet Xanadu, is there a periodic table?

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• Now, look at the atoms.

• What do we see with our eyes?• Why are the atoms made the way they are?

– Color?– Shape?– Weight?– Bonding?

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AtomsWhat data do we have?

• Atomic Force Microscopy– A very sensitive probe is scanned across the

surface, and the force on the probe is measured– By using electronics to keep the force constant,

we can – line by line – generate a profile of the surface

– The best instruments can “feel” individual atoms.

– Conclusion: the world is granular.

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• Atomic Force Microscopy (neat websites)• http://www.mee-inc.com/afm.html • http://www.rhk-tech.com/hall/NaCl-mica.html • http://stm2.nrl.navy.mil/how-afm/how-afm.html • http://www.omicron.de/index2.html?/results/

atomic_resolution_on_si_111_7x7_in_non_contact_mode_afm/~Omicron

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• Atomic Force Microscopy (neat websites)• http://www.mee-inc.com/afm.html • http://www.rhk-tech.com/hall/NaCl-mica.html • http://stm2.nrl.navy.mil/how-afm/how-afm.html • http://www.omicron.de/index2.html?/results/

atomic_resolution_on_si_111_7x7_in_non_contact_mode_afm/~Omicron

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AtomsWhat AFM data do we have?

Silicon surface

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NaCl (salt) surface

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• Conclusion:

– The world “feels” granular.

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AtomsWhat MS data do we have?

• Mass Spectrometry separates atoms (actually ions) according to their differing masses.

• Different masses have different trajectories!

• Real mass spectrometers require a very good vacuum, and they are expensive.

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• Mass Spectrometry separates atoms (actually ions) according to their differing masses.

• Neat websites!• http://www.chem.arizona.edu/massspec/

example_html/examples.html • http://www.cea.com/cai/simstheo/mspectra.htm • http://www.chemguide.co.uk/analysis/masspec/

elements.html

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The different elements have different masses.

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AtomsAFM and MS

• AFM – The AFM box allows students to mimic the measurements made with a real AFM. Maybe you can feel individual atoms?

• MS – The mass spectrometer allows students to mimic the measurements made with a real mass spectrometer. Do you want to see the trajectories of your atoms?

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AtomsMaking Stuff

• What does it cost?

• Atoms -- average cost is about $0.10 per atom (steel costs $0.08 per atom)

• AFM -- $2-5 (most of the cost is velcro)

• MS -- $2

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Should I use this approach in my class?

• It (probably) will help students with the fundamental concepts of chemistry.

• Perhaps you are constrained by the sequencing of chemistry instruction?

• Perhaps you are constrained by TEKS and TAKS?

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• Perhaps you are constrained by the sequencing of chemistry instruction?

• 8th grade ??? [pre-AP chemistry AP chemistry Freshman Chemistry degree in chemistry]

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• Perhaps you are constrained by TEKS and TAKS?

• “Which letter in this model of a boron atom represents a neutron?” (TAKS grade 8 science April 2006)

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What can we do together?

• Longer workshops on this theme?– Get 10 teachers together and ask me– Atoms (and how to make a set)? Density?

Gases and Pressure?

• Course at UTD “Lab and Demonstrations for Middle School” -- Spring 2009

• Research/publication on the effectiveness of this approach?

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If we could see atoms, kids might…

• Help me fill this in…

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Contact Info

Dr. Lynn Melton

Department of Science/Mathematics Education

UT-Dallas

800 W. Campbell Road

Richardson, TX 75080

[email protected]

If we could see atoms, kids might …

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