06-21-051 atoms are fun! lynn a. melton university of texas at dallas june 21, 2005

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Atoms Are Fun!

Lynn A. Melton

University of Texas at Dallas

June 21, 2005

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Morning Schedule

#1 9:00 - 9:20 Models#2 9:20 - 9:40 Seeing Without Seeing*#3 9:40 -10:00 Atoms#4 10:00 - 10:20 Atoms Without Seeing*#5 10:20 - 10:40 Measuring Atoms#6 10:40 - 11:00 Seeing Without Seeing*#7 11:00 – 11:40 Making Stuff*#8 11:40 – 12:00 Does This Model Work? * = “hands on”

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Comments on Schedule

• 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 covered here.

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

• No algebra!

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#1 Models

A model is a step onthe staircase of understanding

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#1 Models

Working scientists use manyof the steps. They use the simplestmodel that works, since the highersteps generally require morecomplex mathematics.

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#1 Models

Models are generally not completely“true”. They generally explain somethings well and other things poorly.

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#1 Models

Which step is best for us?

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#2 Seeing Without Seeing

• Most chemists see atoms moving when they talk about reactions. Maybe they have a “tv screen” in the front of their brain.

• It takes students a long time (sophomore year of college?) to acquire this skill.

• How can we intentionally start to build this skill in younger students?

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• The AFM (“atomic force microscope”) can detect individual atoms.

• AFM is not like conventional microscopes, which use light. It “feels” atoms.

• We have built a classroom AFM, but now AFM stands for “Atomic Force Macroscope”.

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• In your first AFM exercise, you are to graph the arrangement of the atoms, which form a single step layer.– Leave the square blank if it is the base layer– Shade the square if it is the next layer.

• No looking! This is “seeing without seeing”.

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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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• In fifteen minutes,– Create an AFM of your box.– Switch with adjacent team (1 - 2, 3 - 4, etc.)– Check the AFM of the other team, but now A is the

“recorder” and B is the “doer”.– Compare your results.

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#3 Atoms

• A conceptual chemistry problem:• “A piece of normal (dirty) copper wire is held in a

gas flame. It becomes bright copper “pink”. When it is removed from the flame and allowed to cool, it becomes black.

• Question: Does the blackened copper wire weigh more, same, or less than when it was in the flame?”

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#3 Atoms

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

• 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 answer was “more”, “same”, or “less”. She was guessing.

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#3 Atoms

• 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”.• She could reasons well enough, but when she was

asked about atoms, she turned off her reasoning.• The atomic world was ARCANE.

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#3 Atoms

• The atomic world was 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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#3 Atoms

• If a sassy ninth 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 (in #5)

(the world is granular)– Data #2: Mass Spectrometry (in #5)

(the particles have different weights)

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#3 Atoms

• Definition of an atom– 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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#3 Atoms

• 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

• The world is tinkertoys – molecules are built from atoms

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#3 Atoms

• 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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#3 Atoms

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

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#4 AtomsSeeing Without Seeing

• The garbage bag contains models of atoms, but you may not use your eyes to see them.

• Same routine as before, but B starts out as the “doer”. Put both hands in the bag. A starts out as the “recorder”.

• Halfway through switch with your other team (1 – 2, 3 – 4, etc.)

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#4 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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#5 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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#5 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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#5 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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#6 AtomsAFM and MS

• AFM – We have rearranged the atoms in the boxes. This time the arrangement is more than a single step. Maybe you can feel individual atoms?

• MS – Melton has made a mass spectrometer for the atoms in the garbage bag (Unit #4).

• Do you want to see the trajectories of your atoms?

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#7 and #8 AtomsMaking Stuff

• Each team should– Make 100 atoms (enough to use with a class)

• Half heavy and half light

• Half with velcro hooks on one end and neutral on the other end and half with velcro loops on one end and neutral on the other end.

• Melton will demonstrate how to do it

• Use glue gun, backer rod, velcoins, glue sticks, set screws, and scissors.

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• Each team should– Make 100 atoms (enough to use with a class)

• Use glue gun, backer rod, velcoins, glue sticks, set screws, and scissors.

• Everything is available from Walmart, a hardware store except the vecoins and set screws (although 5/8” backer rod may be hard to find).

• Velcoins – Lots of places on the internet but www.feinersupply.com seems to be the cheapest.

• Socket Set screws – 3/8” diameter, ¾” long, look in Yellow Pages for “bolts/screws”

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• Each team should– Make a mass spectrometer

• Examine Melton’s model

• Melton will show you how to cut pvc pipe, bend paper clips, etc.

• Use pvc pipe, pvc tees, rubber bands, paper clips, tape, and creamer cups

• Everything is available from a hardware store or Walmart.

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• Each team should– Make another AFM

• Examine the box (you get to take it home)

• You need insulation tube, cheap flannel, and “industrial strength” velcro hooks (Kay’s Fabrics0

• Everything is available from a hardware store, Kay’s, or Walmart.

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• What does it cost?

• Atoms -- average cost is about $0.10 per atom

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

• MS -- $2

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#9 Does this model work?

• Work for what?– What level of students?– What needs to be accomplished?– Is it affordable?– Is it effective?– Can real teachers use it? Or does it require a

Melton?

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• What is really good about this model?– 1– 2– 3– 4– 5

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• What is really lousy about this model?– 1– 2– 3– 4– 5

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• What should I tell Melton about his model? Now? Later? [email protected]– 1– 2– 3– 4– 5

06-21-051 atoms are fun! lynn a. melton university of texas at dallas june 21, 2005

Documents

measuring atoms

afm exercise

classroom afm

blackened copper wire

copper oxide

layer of avocados

gas flame

single step layer