Transcript Presentation - Chem Chapter Zero

Atoms!
Lynn A. Melton
University of Texas at Dallas
Mini-CAST
January 22, 2011
01-22-2011
1
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!
01-22-2011
2
Fundamental Concepts of
Chemistry
• It’s Tinkertoy® time! [or Fiddlestix®]
• Work in teams; try to be the first team to build a
car. When you think you are finished, the other
teams get to decide whether what you built is
indeed a car.
• 8GBR*: The task of adding a piece rotates
clockwise. One person, one piece, then on to the
next person.
• 8GBR = “eighth grade boy rule”
01-22-2011
3
Fundamental Concepts of
Chemistry
• Atoms
• Bonding/Molecules/Reactions
• Structure/Properties
– Activity of molecule derives from its structure
• All of these are illustrated by the
Tinkertoy® [or Fiddlestix® car].
01-22-2011
4
Some Fundamental Skills
• Ability to work with models
• “Seeing without seeing”
01-22-2011
5
#1 Models
A model is a step on
the staircase of understanding
01-22-2011
6
#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.
01-22-2011
7
#1 Models
Models are generally not completely
“true”. They generally explains some
things well and other things poorly.
01-22-2011
8
#1 Models
Which step is best for us?
01-22-2011
9
#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?
01-22-2011
10
#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?”
01-22-2011
11
#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.
01-22-2011
12
#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 [because the
atoms were too small to reason about].
01-22-2011
13
#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.
01-22-2011
14
#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.”
01-22-2011
15
#3 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)
01-22-2011
16
#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.
01-22-2011
17
#3 Atoms
• Guide the responses away from “Do you
believe in atoms?”
– The word believe has many uses.
• Guide the responses toward “Do you accept,
on the basis of experimental evidence, that
all materials in the world are composed of
atoms?”
01-22-2011
18
#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
01-22-2011
19
#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
01-22-2011
20
#3 Atoms
• What do we need to know about atoms?
– What is your weight?
– What can I build with you?
01-22-2011
21
#4 Atoms
Seeing Without Seeing
• The garbage bag contains models of atoms,
but you may not use your eyes to see them.
– A. Work in pairs, one bag to a pair. One
member of the pair is the “observer”; the other
member is the “recorder”. The observer may
not write; the reporter may not take data.
01-18-11
22
#4 Atoms
Seeing Without Seeing
– B. You many not use your eyes for
observation, feel the contents of the bag.
– C. After “enough” observation, pairs will shift
the bag the next pair. At the time of this
switch, observers become recorders and vice
versa. Do not give out hints.
– D. After “enough” observation, pairs discuss
their observations. If they come to a consensus
about the samples, fine. If not, then back to the
lab(s) for more observations.
01-18-11
23
#5 Atoms
What 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.
01-18-11
24
#5 Atoms
What 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.
01-22-2011
25
#5 Atoms
What data do we have?
•
•
•
•
•
•
Atomic Force Microscopy (neat websites)
http://www.uta.edu/ra/cnm/tutorials/afm_tutorial.html
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_r
esolution_on_si_111_7x7_in_non_contact_mode_afm
/~Omicron
01-22-2011
26
#5 Atoms
What AFM data do we have?
Silicon surface
01-22-2011
27
#5 Atoms
What AFM data do we have?
NaCl (salt) surface
01-22-2011
28
#5 Atoms
What AFM data do we have?
• Conclusion:
– The world “feels” granular.
01-22-2011
29
#5Atoms
What MS data do we have?
• Mass Spectrometry separates atoms
(actually ions) according to their differing
masses. Note: a teacher friend found that
the kids were more comfortable with the
name “mass sorter”. OK with me.
• Different masses have different trajectories!
• Real mass spectrometers require a very
good vacuum, and they are expensive.
01-22-2011
30
#5 Atoms
What 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/ele
ments.html
01-22-2011
31
#5 Mass Spectrum
What well known compound gives rise to this result?
01-22-2011
32
#5 Atoms
AFM 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 [mass sorter]
allows students to mimic the measurements
made with a real mass spectrometer. Do
you want to see the trajectories of your
atoms?
01-22-2011
33
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?
01-22-2011
34
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]
01-22-2011
35
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?
01-22-2011
36
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)
01-22-2011
37