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About this Evaluation Report Content Analysis Instructional Analysis
| [Explanation] This section examines whether the curriculum material's content aligns with the specific key ideas that have been selected for use in the analysis. |
| [Explanation] This section examines whether the curriculum material develops an evidence-based argument in support of the key ideas, including whether the case presented is valid, comprehensible, and convincing. |
| [Explanation] This section examines whether the curriculum material makes connections (1) among the key ideas, (2) between the key ideas and their prerequisites, and (3) between the key ideas and other, related ideas. |
| [Explanation] This section notes whether the curriculum material presents any information that is more advanced than the set of key ideas, looking particularly at whether the “beyond literacy” information interrupts the presentation of the grade-appropriate information. |
| [Explanation] This section notes whether the curriculum material presents any information that contains errors, misleading statements, or statements that may reinforce commonly held student misconceptions. |
Science Interactions states that all matter is made of particles in several places, but no instructional time is devoted to explicating this idea. Not much is done to establish the idea that all matter is made of atoms in course 2, chapter 14, which is primarily about gases, although course 3 deals more with solids and liquids.
The terms “particles,” “atoms,” and “molecules” are used to refer to the smallest constituents of matter. In some cases, the text states that matter is made “of atoms and molecules” (e.g., course 2, chapter 14, p. 428s, A Closer Look; course 3, chapter 7, p. 210s); in other cases, it states that “Matter consists of atoms” (e.g., course 2, chapter 14, p. 446s), or that “matter is made up of molecules” (e.g., course 2, Chapter 19: How Cells Do Their Jobs, p. 586s); and, in one instance (course 3, chapter 7, p. 211s), it refers to the “ions, atoms, or molecules in solid matter” (without any further explanation). Although atoms, molecules, and ions are defined (in course 3, chapter 4, p. 112s and chapter 6, pp. 177s, 181s), the issue of why matter can be composed of atoms, molecules, or ions is never addressed.
Science Interactions does not contrast the atomic theory to naive theories (such as matter being continuous or just including particles), as the statement of the key idea does.
Idea
b: These particles are extremely small—far too small
to see directly through a microscope.
Idea
c: Atoms and molecules are perpetually in motion.
Idea
d: Increased temperature means greater molecular motion,
so most substances expand when heated.
The idea that increased temperature means greater molecular
motion is used also in the explanation of changes of state,
such as in the following explanation of melting: “Heating
a solid causes its particles to vibrate increasingly faster.
Solids melt when the vibrations exert larger forces than
those holding the particles together” (course 3, chapter
7, p. 221s). No activities are presented that link specifically
the idea that increased temperature means greater molecular
motion with increased dissolution or diffusion rates. In
course 3, chapter 7, students observe that hard candy dissolves
quicker in hot water than in cold. However, in the teacher
notes, the suggested answer to the question, “What
can you infer to explain your observations?” does
not link the increased diffusion rate to the increased molecular
motion: “Students should have observed the candy color
spreading most rapidly in the hot water, and inferred that
higher temperature aided that process.... The motion of
water molecules was transferred to the dissolving candy,
which was dispersed to varying extents, depending on how
hot the water was” (p. 209st).
Idea
e: There are 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.
At the end of course 3, chapter 7, a main idea for students
to review is listed: “As temperature changes, matter
changes form. Solid—great forces between particles
restrict their movement to vibration about a fixed point.
Liquid—much weaker forces allow particles to move
faster past each other. Gas—particles are not bound
to each other and move freely” (p. 234s). In this
chapter, the student text mentions twice the strong attraction
of forces between particles of solids and links it to the
definite shape and volume of solids (albeit very briefly).
In addition, the student text notes three times the weaker
attraction of forces between particles of liquids and links
it to the lack of definite shape of liquids as well as to
the property of viscosity. Although the lack of forces between
gas particles is mentioned as a main idea, the student text
does not address this explicitly. The idea that particles of gases are far apart is addressed
(it is mentioned three times in the student text in course
3, chapter 7 and once in course 2, chapter 14. It is linked
cursorily to the low density of gases (course 2, chapter
14, p. 437s) and to the lack of definite shape and volume
of gases (course 3, chapter 7, p. 230s, Figure 7–17).
The idea that particles of solids are closer together is
mentioned a few times briefly and in passing in the student
text; the idea that particles of solids are arranged regularly
is implicit in an enrichment activity in course 3. With regard to the different motions of particles in the
three states, there is a match with the idea that particles
move (see the content analysis for Idea c), although it
is not emphasized that they move in all directions, nor
is the motion of gas particles compared to the motion of
the particles in solids and liquids. In course 3, chapter
7, the student text refers to the motion of the particles
of solids as “vibrations” in several instances
(although it is not noted that they vibrate in all directions).
In addition, there is a representation whose purpose is
to illustrate (among other things) that the particles of
solids vibrate around their rest position (p. 211s, Figure
7–2). The idea that the molecules of liquids are sliding
over and around one another is mentioned a few times, briefly
and in passing, in the student text.
Idea
f: Changes of state—melting, freezing, evaporating,
condensing—can be explained in terms of changes in
the arrangement, interaction, and motion of atoms and molecules. Science Interactions addresses changes of state briefly
in course 1, chapter 4 but does not explain them in terms
of molecular changes. Later, course 3, chapter 7, lists
the objectives: “Discuss melting in terms of kinetic
theory” and “Explain evaporation, condensation,
and sublimation” (p. 208A). However, most of the explanations
focus on the flow of energy into, or away from, a material
(e.g., “The water drops on this window pane form as
water vapor molecules transfer energy to the cold glass
and condense” [course 3, chapter 7, p. 221s]). Other
explanations address briefly (and often implicitly) changes
in the arrangement, motion, or interaction of particles
(e.g., “This chocolate was just heated. Some of the
bonds holding the solid in a regular shape have been broken.
The corners of the block are rounding and smoothing as the
molecules in the chocolate start to move around one another”
[course 3, chapter 7, p. 217s]). However, most of the explanations
of changes of state at the molecular level occur in figures,
rather than in the body of the student text.
The second line of reasoning begins in course 2, chapter 14. A section entitled How Do We Know that Matter Is Made of Atoms? explains that:
Only recently has technology been available that can get even close to seeing a single atom. So how could anyone tell that matter was made of atoms? In the past, scientists had to rely on other experiments to investigate this. The main evidence for the existence of atoms came from chemical reactions. [p. 444s]
Then, the text proceeds to explain the law of definite proportions and argues how it supports the idea that all matter is made up of particles called atoms (Idea a).
Benchmarks for Science Literacy suggests that the law of definite proportions is too sophisticated for grades six through eight (American Association for the Advancement of Science, 1993, p. 77). However, a restrained treatment of this law that focuses on the law of definite composition (illustrated with concrete representations) might help provide evidence that matter is made of atoms, especially as this was a key piece of the thinking that led historically to strong belief in atoms. Unfortunately Science Interactions does not take this approach. Although Science Interactions puts less emphasis on arguments using ratios, it presents arguments in short fragments that do not seem to fit together (e.g., course 2, chapter 14, p. 440st, Find Out! Activity; pp. 442–443st, Design Your Own Investigation: An Atomic Model; pp. 444–445s, text; pp. 444–445s, Figure 14–9). Furthermore, no instructions are provided for the teacher as to how to integrate the fragments.
The experiences that students have with the key ideas generally move from descriptive and macroscopic to explanatory and molecular. For example, students deal with changes of state at the macroscopic level in course 1, then revisit changes of state at the molecular level in course 3. In course 2, the properties of gases are described at the macroscopic level first, before a molecular explanation is given. However, in several instances, students do not appear to encounter ideas in progressively higher levels of sophistication. In some cases, ideas are merely repeated (rather than being revisited explicitly or extended clearly to new contexts). For example, Science Interactions explains gas pressure at the molecular level in both courses 2 and 3 without any clear progression from one course to the other. In other cases, the logic of the progression is not clear. For example, in course 2, chapter 14, section 14–1 presents the properties of gases and gas laws. Section 14–2 presents the ideas that gases are made of particles, that gas particles move, and that the temperature of the gas is proportional to the average kinetic energy of the gas particles. Then, the properties of gases are explained at the particulate level, but not the gas laws. The gas laws are addressed again in course 3, at both macroscopic and microscopic levels.
Science Interactions does not provide tasks, questions, or text that tie together clearly the experiences that students have with a particular idea. For example, in course 1, the properties of solids, liquids, and gases are described in some detail, and several phenomena that relate to these properties are included. In course 3, when these properties are explained at the particulate level, students are not reminded about the experiences they had with these properties in course 1. In course 2, the kinetic molecular theory is introduced in the context of gases. In course 3, the theory is introduced in the context of solids and liquids, as if students had never encountered it before. In addition, presentations of the behavior of gases and the gas laws are not associated with presentations of the same key ideas in course 2.
Like every chapter in Science Interactions, the chapters that relate closely to the kinetic molecular theory contain many components (Theme Connection, Across the Curriculum, Life Science Connection, Technology Connection, Science & Society, and Connecting Ideas) whose objectives are to highlight connections among different topics, concepts, and everyday life applications. Some of these connections are in the body of the student text, others are in the notes to the teacher, and still others are given at the end of each chapter. However, several of these components are not clear about the relationships that they are trying to develop. For example, in course 3, section 7–2: Kinetic Theory of Gases, the following Theme Connection appears: “The behavior of a gas is directly related to the kinetic energy of its molecules. For example, when a gas is heated, the kinetic energy of its molecules increases. This results in more collisions between molecules and thus increased pressure” (p. 226t). In addition, given that connections often do not relate to the main ideas in the chapter, they may disrupt the flow of the main ideas and draw attention away from the key ideas.
A few interesting connections to the kinetic molecular theory appear in chapters that are not related directly to this theory. For example, in course 2, chapter 19, Section 19–1: Traffic In and Out of Cells, a connection is made between the idea that molecules are always moving (presented earlier in chapter 14) and the idea that every cell is covered by a membrane that controls what can enter and leave the cell. First, students are reminded that they have learned that all cells are covered by a thin membrane as well as that “All matter is made up of molecules that are constantly moving...” (pp. 584s, 586s). Then, the latter idea is used to explain diffusion in general and diffusion across the cell membrane in particular. Interspersed in the text are activities that engage students in firsthand experiences that illustrate diffusion and model the action of the cell membrane. The connection between molecular motion and materials moving in and out of cells is explicit and detailed, the connection is explained, and students are engaged in making the connection.
The evaluation teams’ collective findings, presented below, should be taken as having general applicability to all of the evaluated materials, not complete and specific applicability in toto to any one of them.
Identified errors occur most frequently in drawings and other diagrams. They take the form of representations that are likely to either give rise to or reinforce misconceptions commonly held by students. Following are physical science examples of the kinds of misleading illustrative materials of most concern to the evaluation teams:
- Diagrams and drawings that show atoms or molecules of
solids, liquids, and gases in colored backgrounds (for
example, water molecules inside blue drop shapes) and
that thereby can initiate or reinforce the misconception
that particles are contained in solids, liquids,
and gases, in contrast to the correct idea that substances
consist of particles (with empty space between particles).
This misconception may be further reinforced by the wording
of diagram labels, such as “solid particles in
solid water and water particles in liquid
water” (emphasis added). Similarly, statements such
as “explanations for what is inside things”
may imply that matter contains particles (as well as other
things), rather than that matter is made of particles.
- Diagrams of solids (and occasionally liquids) that do
not depict the motion of atoms or molecules can give rise
to, or reinforce, the misconception that atoms or molecules
of solids (or liquids) are still.
- Diagrams that show molecules of liquids much farther
apart than the molecules of solids are misleading; in
most liquids, molecules are only a little farther apart.
- Diagrams that show particles of a substance in the solid, liquid, and gaseous state in different colors can reinforce the erroneous idea that the particles themselves are different, not their arrangement and motion. Similarly, diagrams that show particles of a substance changing size as the substance changes state can give rise to the misconception that the molecules themselves change size, becoming larger when heated.
The use of imprecise of inaccurate language is problematic in text materials, not soley in illustrations. Specifically, language that does not maintain a clear distinction between substances and atoms or molecules can mislead students to attribute macroscopic properties or behavior (such as hardness, color or physical state) to individual atoms or molecules. For example, statements such as “the particles of perfume are moving farther apart as they change into a gas and diffuse throughout the air,” “write a story from the point of view of a particle in the solid phase as it melts and then evaporates,” and “draw what happens when the particles change state” (emphasis added) imply inaccurately that the particles themselves change state (melt, evaporate, etc.).
