Atoms!

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Atoms!

• Lynn A. Melton
• University of Texas at Dallas
• Mini-CAST February 21, 2009

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Website

• http//www.chemchapterzero.com
• 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!

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Fundamental Concepts ofChemistry

• Atoms
• Bonding/Molecules/Reactions
• Structure/Properties
• Activity of molecule derives from its structure

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Some Fundamental Skills

• Ability to work with models
• Seeing without seeing

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1 Models
A model is a step on the staircase of
understanding
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1 Models
Working scientists use many of the steps. They
use the simplest model that works, since the
higher steps generally require more complex
mathematics.
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1 Models
Models are generally not completely true. They
generally explains some things 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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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 made of atoms? After all, I
  cannot see atoms.

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3 Atoms

• Your answer has three parts
• Define an atom carefully
• Data 1Atomic 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 dont ask, dont
  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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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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AtomsWhat data do we have?

• 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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AtomsWhat AFM data do we have?
NaCl (salt) surface
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AtomsWhat AFM data do we have?

• 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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AtomsWhat MS data do we have?

• 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/elemen
  ts.html

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5 AtomsWhat MS data do we have?
The different elements have different masses.
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Mass Spectrum
What well known compound gives rise to this
result?
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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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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?

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Should I use this approach in my class?

• 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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Should I use this approach in my class?

• It (probably) will help students with the
  fundamental concepts of chemistry.
• Perhaps you are constrained by TEKS and TAKS?

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Should I use this approach in my class?

• 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)