| Earth Science | Life Science | Physical Science |
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. |
Chapter 3: Physical and Chemical Changes proceeds as if students are familiar with particles already and explains the properties of solids, liquids, and gases in terms of the arrangement and motion of particles in the three states. Chapter 4: Mixtures, Elements, and Compounds defines atoms and molecules briefly (“The smallest particle of an element that has the properties of that element is called an atom. An atom is the basic building block of matter” [p. 97s]; “A molecule is the smallest particle of a compound that has all the properties of that compound” [p. 101s]). Chapter 5: Atoms: Building Blocks of Matter starts with a large photograph of beads of mercury (p. 110s). This question is posed nearby: “Is there some incredibly tiny bead of mercury that if sliced one more time would no longer be mercury?” (p. 111s). Teachers are to point out that scientists named the single smallest particle of matter an atom (p. 110t). The text on the following pages gives Democritus’ answer to the question:
After much observation and questioning, Democritus concluded that matter could not be divided into smaller and smaller possible pieces forever. Eventually the smallest possible piece would be obtained. This piece would be indivisible. Democritus named this smallest piece of matter an atom. [p. 113s]
These statements explain what an atom is but stop short of explicitly stating the idea that matter is composed of collections of large numbers of such smallest pieces. Chapter 7: Atoms and Bonding, in the context of describing chemical bonding, explicitly states the idea: “[A]ll matter—regardless of its size, shape, color, or phase—is made of tiny particles called atoms” (p. 174s). Chapter 17: What Is Heat? in the context of linking heat to the motion of molecules, mentions that “matter is made up of tiny particles called molecules, which are always in motion” (p. 425s).
In this textbook, the atomic theory is not contrasted to naive theories (such as matter being continuous or just including particles), as it is in the statement of the key idea. An activity in chapter 3 asks students to fill a beaker with marbles that represent particles in a liquid (or a solid) (p. 66st). Next, the students pour sand and then water into the beaker, which is intended to demonstrate that there are spaces between the particles in a solid or a liquid. This activity is not explicitly related to the key idea. For example, the text does not relate the representation to the particulate nature of matter, nor does it ask the students to do so. Further, this activity may prompt the misconception that the particles are in continuous matter, rather than clarify the notion that matter consists of particles and that there are empty spaces between the particles.
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. In addition to associating temperature with the motion
of molecules, the material links temperature to the energy
of molecules. In Chapter 17: What Is Heat? the caption for
Figure 17–9 (showing a geyser) states: “Heat
within the Earth increases the kinetic energy of water molecules
so that they escape from the Earth as an eruption of hot
water and steam” (p. 431s). The suggested response
to the caption’s assertion about the relationship
between heat and temperature, “Heat energy increases
the average kinetic energy, which causes a rise in temperature”
(p. 431t), is likely to be confusing. Not only does it not
specify that it refers to the average kinetic energy of
molecules, but also it implies a causal relationship between
the increase in the average kinetic energy of molecules
and the temperature increase. On the following page, temperature
is defined as “a measure of the average kinetic energy
of molecules” (p. 432s). Later in the chapter, the
student text explains thermal expansion in solids in terms
of the kinetic energy of the molecules: “As heat energy
is added to the solid, the kinetic energy of the molecules
increases and their vibrations speed up” (p. 444s).
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.
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.
Changes of state appear both in Chapter 3: Physical and
Chemical Changes and in Chapter 17: What Is Heat? Chapter
3 includes an explanation of phase changes in general as
well as explanations of specific phenomena related to melting,
freezing, evaporation, boiling, and condensation (pp. 69–75s).
Most of these explanations refer only to the flow of energy
into or away from a material (such as those for freezing
and condensation [pp. 71s, 73s]) or talk solely about particles
absorbing heat energy (such as those for evaporation and
boiling [p. 72s]), rather than changes in the arrangement,
interaction, and motion of atoms and molecules. The general
description of phase changes refers to changes in the arrangement
and motion of particles somewhat explicitly (“What,
then, causes the particles of a substance to be in one particular
phase rather than another? The answer has to do with energy—energy
that can cause the particles in a substance to move faster
and farther apart” [p. 69s]), and the account of melting
implies changes in the arrangement and motion of particles
(“The rigid crystal structure of the particles breaks
down, and the particles are free to flow around one another”
[p. 70s]). Finally, a phase-change diagram shows colored
dots close together and arranged regularly in a solid, less
so in a liquid, and even less so in a gas, but there is
nothing in the accompanying text that notes what the colored
dots represent (p. 74s). Chapter 17 includes an explanation of ice melting in terms
of the interaction of molecules (“When ice melts and
changes into water, energy in the form of heat is being
absorbed by the ice. The energy is needed to overcome the
forces of attraction that hold the water molecules together
in the solid phase [ice]” [p. 440s]).
In general, students do not encounter these ideas in progressively higher levels of sophistication. On the contrary, ideas are introduced without preparation or are merely repeated (rather than being revisited explicitly or extended clearly to new contexts). For example, Chapter 3: Physical and Chemical Changes relies on the concepts of heat, energy, and temperature; however, these concepts are not taught until chapters 16 and 17. Chapter 17: What Is Heat? includes a section on phase changes without linking it to the description and explanation of phase changes in chapter 3.
Furthermore, the material does not provide tasks, questions, or text that tie together clearly the experiences that students have with the same idea. For example, when states of matter and changes of state are introduced first in chapter 3, the term “particle” is used to represent specks of dust in the air (pp. 60–61t), particles of dirt (p. 66t), and the smallest constituents of matter—atoms and molecules (p. 62s). When elements and compounds are introduced in chapter 4, the text merely states that atoms are the smallest particles of elements (p. 97s) and that molecules are the smallest particles of compounds (p. 101s). No attempt is made to connect separate statements about the same idea or to help students see that these particles are the same particles referred to in chapter 3 on the states of matter. Furthermore, with regard to the question, “What is an atom?” the suggested answer in the teacher’s notes does not use the word “particle” (pp. 99s, 98t). Instead, it defines an atom as the smallest part of an element.
The material makes some conceptual connections among ideas; however, the connections are often implicit, brief, and difficult to locate. For example, on page 215s, an opportunity is missed to connect chemical reactions explicitly to the constant motion of molecules. Later, though, the idea that increased temperature means increased molecular motion is connected explicitly (and adequately) to the fact that an increase in temperature generally increases the rate of reaction (p. 217s).
The Teacher’s Guide at the front of the Teacher’s Edition includes a matrix that links seven themes (energy, evolution, patterns of change, scale and structure, systems and interactions, unity and diversity, and stability) to an “overarching concept statement, as to how that particular theme is taught in the chapter” (p. T–4). For example, in Chapter 3: Physical and Chemical Changes, the theme of scale and structure is linked to the idea that “The properties of solids, liquids, and gases are related to the arrangement of particles that make up the substance” (p. T–7). However, the theme of scale and structure is not described, nor is it specified how the idea is linked to that particular theme.
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.).
