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ACS: Matter – Solids, Liquids, and
Gases: Introducing a Free Online
Resource for Middle School Chemistry
Presented by: James Kessler
May 24, 2012
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Middleschoolchemistry.com
Big Ideas about the Very Small
Chapter 1:
Matter – Solids, Liquids, and Gases
Welcome
What is middleschoolchemistry.com?
Six chapters of activity-based lesson
plans that align with state standards and
national frameworks in physical science
and inquiry.
Two main goals:
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•
Help students understand and be
able to explain basic chemistry
concepts on the molecular level.
•
Help students to design and conduct
valid scientific experiments.
What’s in a Chapter?
•
Fully-developed 5-E Lesson
Plans
– Hands-on Activities
– Student Activity Sheets
– Multimedia
– Extra Teacher Background
•
Student Reading
•
Test Bank
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Goals of the Webinar
•
Demonstrate how the activities and
animations from the lessons in Chapter 1 can
be used with students
•
Review basic chemistry concepts covered in
the Chapter 1 lessons
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Big Idea for Chapter 1:
Why are different substances solid, liquid, or gas at room
temperature?
Use the “Fascination Number Line” to input your level of fascination
with this question.
Have never
thought about it
and happy that
way
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Willing to listen if
it doesn’t take too
long
Stay up nights
pondering this
question
Lesson 1.1
Molecules Matter
Engage
Explore
Explain
What are some examples of matter?
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Evaluate
Extend
Attractions between Water
Molecules
Engage
Explore
Explain
Evaluate
Extend
Students observe water on
wax paper.
Does the water drop stay
together or come apart
easily?
If water was made of tiny
particles (molecules), would
you say they are attracted to
each other or not?
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The Motion of Water Molecules
Engage
Explore
Explain
Evaluate
Extend
What else can we learn about the particles that make up water?
Why do you think the
food coloring spread
out?
If the food coloring is also
made of particles, how
could the water molecules
help to spread them out?
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Molecular Model Animation - Liquid
Engage
Explore
Explain
Evaluate
Extend
Attractions keep molecules
close together.
Molecules are in motion and
move past each other.
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Drawing a Model of a Liquid
Engage
Explore
Explain
Evaluate
Extend
The student activity sheet serves as the “Evaluate” for each lesson.
Students draw a model of
water molecules and a
caption to describe what
their model represents.
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Effects of the Attractions of Water
Molecules
Engage
Explore
Explain
Evaluate
Extend
Why do you think the water
keeps its shape the moment
the balloon is popped?
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Play a Water Game
Engage
Explore
Explain
Evaluate
Let’s play “Water Drops Unite” & “Race Drop Raceway”
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Extend
Why are Water Molecules
Attracted to Each Other?
The water molecule is composed of
two hydrogen atoms bonded to an
oxygen atom.
These are covalent bonds in which
electrons are shared between the
oxygen atom and the hydrogen
atoms.
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Water Molecules are Polar
In the bonds in a water molecule, the
electrons are not shared equally.
The electrons are more attracted to the
oxygen atom than to the hydrogen atoms.
This makes water a “polar” molecule.
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Water Molecules Attract Each Other
Water molecules attract one another
according to their opposite polar ends.
This accounts for the cohesion between
water molecules and gives water many
of its characteristic properties.
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Let’s pause for questions
from the audience
Lesson 1.2
Heating and Cooling Water
Ask students: What do you think you could do to the water to make the
water molecules move faster?
If you wanted to test whether heating
or cooling water affects the motion of
the molecules, how could you do it?
How would we make sure our test is
fair?
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Heating and Cooling Water
On the molecular level, why does heating the water affect how fast
the food coloring mixes in the water?
Adding or removing energy affects the
speed of molecules:
• Heating a liquid increases
molecular motion
• Cooling a liquid decreases
molecular motion
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Moving Molecules
Aside from moving faster or slower, what else changes about water
molecules as the temperature changes?
Add energy:
• Faster motion competes
with attractions
• Further apart
Remove energy:
• Slower motion competes
with attraction
• Closer together
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Liquid
Characteristics of a liquid on the molecular level
• The molecules of a liquid move at a certain speed at room
temperature.
• The attractions between the molecules are strong enough to
keep them close together at that speed.
• Adding energy (heating) makes molecules move faster, causing
them to move a little further apart.
• Removing energy (cooling) makes molecules move slower,
causing them to move a little closer together.
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Lesson 1.3
An Application of Molecular
Motion in Liquids: Thermometers
Students place a thermometer in hot and then
cold water.
Ask students to explain, on the molecular level:
• Why the liquid goes up when a thermometer
is placed in hot water?
• Why the liquid goes down in cold water?
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How Thermometers Work
• Hot: faster, further apart, move up
• Cold: slower, closer together, move
down
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Let’s pause for questions
from the audience
Lesson 1.4
Molecular Motion in Solids
Do the same principles that apply to liquids also apply to solids?
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Heating and Cooling a Solid
Ask students: If solids are also
made of atoms and molecules,
try to explain why this happens
on the molecular level.
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Solids vs. Liquids
•Vibrate
•Attracted to each other
•Don’t move past each other
Assume that the solid and liquid
are both at room temperature.
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Heating and Cooling a Solid
• Hot: faster, further apart
• Cold: slower, closer together
Flexible joints in roads keep the
road from cracking as it expands
and contracts with changes in
temperature.
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How are the Atoms of a Metal
Attracted to Each Other?
The atoms of a metal are
attracted to one another in a
way called “metallic bonding.”
The outer electrons move
between the metal atoms
(positive ions).
The attraction between the
positive metal ions and the
negative electrons holds the
metal together as a solid.
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Solid
Characteristics of a solid on the molecular level
• The atoms or molecules of a solid move at a certain speed at
room temperature.
• The attractions are strong enough to keep them close together at
that speed and to hold them in fixed positions as a solid.
• Adding energy (heating) increases the motion of the atoms
causing them to move a little further apart.
• Removing energy (cooling) decreases the motion of the atoms
causing them to move a little closer together.
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Let’s pause for questions
from the audience
Gases Are Matter, Too
Air is made up of molecules of
different gasses. It is about 78%
nitrogen and about 20% oxygen.
These molecules have mass and
take up space.
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Lesson 1.5
Molecular Motion in Gases
• Very far apart
• Very weak attractions
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Heating and Cooling a Gas
The mouth of an “empty”
bottle is dipped into a
detergent solution.
The bottom of the bottle is
placed in hot water and then
in cold water.
On the molecular level, why
does this happen?
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Modeling Heating and Cooling
a Gas
• Outside air pressure is the same on both.
• The faster-moving molecules in the heated
sample push harder against the air pressure and
expand the bubble.
• The slower-moving molecules in the cooled
sample push less hard against the air pressure,
which causes the bubble to contract.
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Heating and Cooling a Gas
• Warmer, faster moving
molecules push harder from
the inside against the bubble
film than the air pressure
pushes from the outside.
• Cooler, slower moving
molecules don’t push as hard
as the outside air pressure,
which pushes the bubble down.
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Why Are the Molecules of the Gases
in Air Not Attracted to Each Other?
Nitrogen gas (N2)
Oxygen gas (O2)
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Nitrogen (N2) and oxygen (O2) gas are made
of two identical atoms bonded together. Each
atom attracts the electrons of the other
equally. There is no polarity like in the water
molecule.
Gas
Characteristics of a gas at the molecular level
• The molecules of a gas move at a certain speed at room temperature.
• The attractions between the molecules are not strong enough at that
speed to keep them close together as a liquid or a solid; therefore,
they move independently as a gas.
• Adding energy (heating) increases the motion of the molecules and, if
they can, they move further apart.
• Removing energy (cooling) decreases the motion of the molecules
and, if pushed on hard enough, they move closer together.
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Student Understanding - Balance
Between Attraction and Motion
Different substances are solid, liquid, or gas at a particular temperature
because of a balance between the attractions of the atoms or molecules of
the substance and their motion at that temperature.
Poor
Understanding
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Moderate
Understanding
Good
Understanding
39
Do the Lessons Align with the New
National Framework for Science
Education?
Disciplinary Core Ideas
• The position and motion of atoms or molecules in a solid, liquid, and gas.
Science and Engineering Practices
• Developing and using models.
• Planning and carrying out investigations.
• Constructing explanations based on evidence.
Crosscutting Concepts
• Cause and effect: Adding or removing energy (heating and cooling)
causes changes in the motion of molecules.
• Systems and system models: Students model substances as systems
composed of particles.
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For more resources …
www.middleschoolchemistry.com
For more information, contact us at k8education@acs.org
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