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Idea a: All
matter is made up of particles called atoms and molecules (as
opposed to being continuous or just including particles).
There is a content
match. The idea that matter is made up of particles is an explicit
learning goal of Matter and Molecules (Science Book,
Goal Conceptions, pp. T-14, T-27, T-40; Lesson Objectives, pp.
T-11, T-26) and is presented in different contexts and in several
locations in the student and teacher materials. After students
describe ice, liquid water, and water vapor as states of the
same substance, molecules are introduced as the tiniest parts
of water (Science Book, pp. 2-7s). Students learn that
all three states of water are the same in that they are made
of water molecules that are moving constantly. A representation
of molecules viewed through magic eyeglasses is shown to give
students a concrete picture of what the molecules might look
like if they could be seen (Science Book, p. 5s). Next,
students are introduced to the idea that other substances (such
as lead, sugar, alcohol, and air) are made of molecules (Science
Book, pp. 13-20s). The student text explains that different
substances are made of different kinds of molecules (Science
Book, pp. 13–16s) and describes pure substances as being
made of a single kind of molecule, with mixtures consisting
of two or more different kinds of molecules (Science Book,
pp. 17–18s). The generalization that all matter is made of molecules
is advanced and contrasted to things that are not matter, and
therefore are not made of molecules (such as forms of energy)
(Science Book, p. 15s). Magic eyeglasses are used to
reinforce the molecular composition of all substances
(Science Book, pp. 15s, T-30, T-32, T-35). The remaining
lesson clusters
make use of the idea of molecular composition, along
with the ideas of molecular arrangement, motion, and interaction,
to explain a variety of physical phenomena, such as the compression
of gases, dissolving, thermal expansion, and changes of state.
In most cases, the
small, seemingly invisible pieces of matter are labeled as "molecules."
In Lesson Cluster 2, atoms as components of molecules are introduced
briefly to convey the idea that different arrangements
of atoms into molecules compose different substances (Science
Book, p. 14s). Unfortunately, no statements contrast the
idea that all matter is made of particles with the naïve
idea that matter is continuous. However, the idea that matter
is made of molecules is contrasted with the naïve idea
that matter just includes molecules, and the fact that
there is empty space between a substance’s molecules is stressed
repeatedly.
Idea b: These
particles are extremely small—far too small to see directly
through a microscope.
There is a content
match. This idea is a specific learning goal of Matter and
Molecules (Science Book, Goal Conceptions, pp. T-14,
T-27, T-40). The extremely small size of molecules is discussed
in the student text. Furthermore, this idea is seen in the context
of questions posed to students in the Activity Book and
in the notes and suggestions in the Teacher’s Guide.
In Lesson Cluster
1, the incredibly small size of molecules is explained in statements
such as "every drop of liquid water—and every sliver of
ice—is made of trillions of water molecules…" and "In
fact, a typical cell in your body might be made of 100 trillion
(100,000,000,000,000) molecules" (Science Book,
p. 6s). Although the text explains that molecules are much smaller
than things such as specks of dust and things that can be seen
only with a microscope, such as cells and germs, the student
text does not state explicitly that molecules cannot be seen
with a microscope.
The small size of
molecules is mentioned periodically throughout the rest of the
unit in both the student text and in the Teacher’s Guide.
For example, Lesson Cluster 2 explains that "Even the largest
molecules, though, are far too small to see" (Science
Book, p. 14s). When students are asked whether one can tell
a pure substance from a mixture by looking at the molecules
with a magnifier, the suggested response is: "You could
tell the difference between pure substances and mixtures if
you could see molecules with a magnifier. But you cannot see
molecules with a magnifier" (Activity Book, p. T-9,
question 2). Likewise, when students are asked about seeing
"dust molecules in the air" the suggested response
is that "…a speck of dust is huge compared to a molecule…
A molecule is so tiny you cannot see it even with a microscope"
(Activity Book, p. 11s, T-11). Also, in the context of
sugar dissolving in water, students are asked whether the holes
in a tea bag are big enough for molecules of sugar to get through
them. The teacher notes suggest: "You might point out here
that molecules are much smaller than grains. Grains of sugar
are made of trillions of molecules" (Activity Book,
p. T-25).
Idea c: Atoms
and molecules are perpetually in motion.
There is a content
match. The idea that all molecules are moving constantly is
one of the learning goals of Matter and Molecules (Science
Book, Goal Conceptions, pp. T-14, T-27, T-40, T-48, T-61,
T-69; Lesson Objectives, p. T-47). In Lesson Cluster 1, the
idea is introduced that water molecules in solid, liquid, and
gaseous states are always moving and that they never stop (Science
Book, pp. 7–8s). In Lesson Cluster 2, the different kinds
of motions of molecules in the three phases (solid, liquid,
and gas) of all substances are presented. In Lesson Clusters
3 through 5, students use the idea of molecular motion to explain
a variety of phenomena, such as the dissolving of sugar in water,
the diffusion of gases (such as perfume, ammonia, and other
smells), and the tendency of gases to occupy all of the space
available to them (e.g., when the valve in a scuba tank is opened,
the air rushes out; one can hear it making a rushing noise).
Furthermore, in several instances, the Teacher’s Guide
suggests that teachers emphasize the idea that molecules are
moving constantly. For example, when the motion of molecules
in the three states of water is introduced in the student text,
teachers are reminded to explain that "molecules are constantly
moving and never stop, even in a solid" (Science Book,
p. T-21).
Idea d: Increased
temperature means greater molecular motion, so most materials
expand when heated.
There is a content
match. The ideas that "molecules of hot substances move
faster" and that "increased motion moves molecules
farther apart" are explicit learning goals of Matter
and Molecules (Science Book, Goal Conceptions, pp.
T-69, T-80, T-100). Lesson Cluster 6 explains and represents
the idea that "heating any substance makes the molecules
of that substance move faster" (Science Book, p.
39s). In the first activity of lesson 6.1, students are to predict,
observe, and then explain (in terms of molecules) why hard candy
dissolves faster in hot water than in cold water. Then, the
student text proposes the idea that when molecules move faster,
they move farther apart and has the students explain various
solid, liquid, and gas expansion phenomena in terms of molecules.
In Lesson Clusters 7 through 9, the text uses the idea that
"molecules of a substance move faster when the substance
is heated, and slower when it is cooled" (Science Book,
Key Elements of a Good Explanation, item 1, p. T-78) to explain
changes of state. However, the student text does not relate
temperature to the greater average energy of motion.
Idea e: Differences
in the arrangement and motion of atoms and molecules in solids,
liquids, and gases: In solids, particles (1) are packed closely,
(2) are (often) arranged regularly, (3) vibrate in all
directions, (4) attract and "stick to" one
another. In liquids, particles (1) are packed closely,
(2) are not arranged regularly, (3) can slide past one another,
(4) attract and are connected loosely to one another.
In gases, particles (1) are far apart, (2) are
arranged randomly, (3) spread evenly through the spaces
they occupy, (4) move in all directions,
(5) are free of one another, except during collisions.
There is a partial
content match. The different arrangement and motion of molecules
in the solid, liquid, and gaseous states are explicit learning
goals of Matter and Molecules (Science Book, Goal
Conceptions, pp. T-14, T-27; Lesson Objectives, pp. T-11, T-26).
The idea that "molecules of one substance attract each
other" is also a learning goal (Science Book, Goal
Conceptions, pp. T-80, T-100), but how the attraction differs
in the three states is not a learning goal.
Lesson Cluster 1
describes and represents with diagrams the different arrangement
and motion of water molecules in the solid, liquid, and gaseous
states. Lesson Cluster 2 generalizes this difference in the
solid, liquid, and gaseous states to all other substances. Although
many diagrams show the molecules of solids, liquids, and gases
moving in all directions, no statement in the text explains
this point. Furthermore, the text says that the different arrangement
and motion of molecules can explain the different properties
of the three states, but it does not explain any specific properties.
In Lesson Cluster
4, several activities target the idea that air molecules are
far apart. For example, students observe differences in compressibility
between air and water and explain these differences in terms
of the differences in the proximity of their molecules. This
cluster also introduces the idea that air molecules (e.g., in
a syringe or a bicycle tire) spread evenly through the spaces
they occupy (rather than "bunch up together in one place
more than another place" [Science Book, p. 33s]).
The student text describes the concept of forces of attraction
between water molecules to explain how liquid water freezes,
and, later, how liquid water evaporates and water vapor condenses.
However, the student text does not state precisely that there
are forces of attraction among the molecules of all substances
(even though students are expected to use this idea as they
explain how other substances solidify and evaporate). Also it
is never said specifically that molecules of gases are free
of one another, except during collisions. Although, occasionally,
gas molecules are described as moving "freely in space,"
this phrase is not explained.
Idea f:
Explanations of changes of state—melting, freezing, evaporation,
condensing, and perhaps dissolving—in terms of changes in the
arrangement, interaction, and motion of atoms and molecules.
There is a content
match. Explanations of changes of state—melting, freezing, evaporating,
and condensing—in terms of changes in the arrangement, interaction,
and motion of molecules are explicit learning goals of Matter
and Molecules (Science Book, Goal Conceptions, pp.
T-61, T-80, T-90, T-100; Lesson Objectives, pp. T-59, T-78,
T-87, T-97). The student text includes several step-by-step
explanations of the melting, freezing, evaporation, boiling,
and condensation of water in terms of changes in the arrangement,
interaction, and motion of its molecules. In addition, students
are asked to explain a large number and variety of phenomena
involving changes of state, such as the melting and solidifying
of various kitchen substances, the evaporation of alcohol, solar
stills, and the water cycle.
Idea g: Connection
between increased temperature and increased energy. Increased
temperature means greater average energy of motion, so most
substances expand when heated.
The text explains
thermal expansion by increased molecular motion, rather than
by increased energy—a more abstract concept. Please see comments
under Idea d.
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