Proc. Natl. Sci. Counc. ROC(D) Vol. 12, No. 3, 2002. pp. 91-99 Using Cognitive-based Dynamic Representations to Diagnose Students’ Conceptions of the Characteristics of Matter * ** MEI-LING CHIU , MEI-HUNG CHIU , AND CHIA-YEN HO ** *Affiliated Senior High School National Taiwan Normal University Taipei, Taiwan, R.O.C. **Graduate Institute of Science Education National Taiwan Normal University Taipei, Taiwan, R.O.C. (Received October 17, 2002; Accepted April 9, 2003) ABSTRACT Numerous studies have shown that learners at different levels and ages have difficulties understanding science concepts. Such difficulties are revealed by students’ alternative conceptions generated during instruction. The reasons for these difficulties have some common features, such as students’ complex, abstract, and inconsistent intuition about those science concepts. In chemistry, this also holds true for many fundamental concepts (e.g., the structure and motion of atoms and molecules; the behaviors of particles in gas, liquid, and solid states). To understand the knowledge structure held by the tenth graders involved in this study, we first conducted openended and semi-structured interviews, followed by a paper-and-pencil test covering the arrangements and behaviors of particles in three states (solid, liquid, and gas). We followed this with more interviews to hear their explanations for each answer for the sake of developing multiple-choice test items based on the learners’ understanding of chemistry. Using the results from the first stage, we designed a software program with dynamic representations to help us investigate what representative knowledge the learners had of chemistry concepts and how they explained the concepts. The students were tested individually in a computer lab. Each student worked at his or her own computer and answered the questions so as to best reflect his or her understanding. The findings revealed that the students were able to identify the static structures of particles in three states. They were also able to distinguish the differences in particles’ motion between the solid and gas states. However, about 15 percent of the students believed that particles in a solid are static. In addition, more than half of the students believed that the motion of particles in a liquid was the same as that in a solid. Reasons for their choices were also examined. Implications for learning and instruction are discussed. Key Words: dynamic representation, matter, conception I. Introduction Active constructing and restructuring of knowledge plays an essential role in learning. Students generate their understanding via the interaction between their existing knowledge structure and new information that might have representations of concepts that are different from their original ones. The gap between the existing and the new knowledge framework creates the difficulties in learning science. This is more obvious in the learning of abstract concepts in chemistry. Johnstone (1991) considered that chemistry instruction should include macroscopic, microscopic, and symbolic levels. Of these, the microscopic level is the essence of chemistry teaching. However, studies focusing on the concept of “basic” particles (e.g., Ben-Zvi, Eylon, & Silberstein, 1986, 1988; Gabel, 1993; Johnson, 1998; Novick & Nussbaum, 1978, 1981) revealed that despite a great deal of instruction emphasizing particle theory, many pupils (at all ages) consistently showed that they had difficulties or incomplete understanding of basic particle theory. For instance, Stavy (1990) showed that even when seventh and eighth graders were taught the concepts of particles in their science curricula, only about 15% of eighth and ninth graders who had studied under the same curricula were able to use the composition and arrangement of particles to explain phase changes. Seventh graders were completely unable to explain phase changes. Since Craik (1943, cited in Johnson-Laird, 1989) first − 91 − M.L. Chiu et al. proposed the concept of mental models to refer to a special kind of mental representation, many researchers have given definitions of mental models (e.g., Gentner & Stevens, 1983; Norman, 1983; Vosniadou, 1994). Although the definitions vary, the idea underlying mental models involves its intrinsic descriptions of observations or byproducts of actual interaction between one’s understanding and a stimulus. Research has shown that there is a close relationship between one’s mental models and concrete representations (such as physical models, simulation, or symbols). In this study, we were mainly interested in investigating students’ mental models of the behaviors and structure of particles in solids, liquids, and gases using dynamic representations shown on computers. interviewed the students about particles using open-ended questions to obtain original responses. Second, we developed multiple-choice items based on the data drawn from the students. Third, we conducted a paper-and-pencil test using the drawings from the students. Once the test was completed, we interviewed the students again to verify the answers. Whenever needed, we interviewed the students to obtain more in-depth explanations of their answers to validate multiple-choice items. The merit of this design was that the test items were primarily chosen based on the students’ drawings or explanations of their understanding of particles. These multiple research methods were iteratively used in this study. 2. Subjects Research Questions (1) What were the misconceptions that tenth graders held about the particulate nature of a substance in different states? (2) What characteristics of those misconceptions were in nature? II. Description of the Research and Methodology This study was part of a larger project that investigated how students at different levels understood chemistry concepts in terms of their mental models. The main purpose was not to “assess” the students’ performance, but rather to “diagnose” their alternative conceptions of particles. In this study, we tried to develop test items based on students’ alternative frameworks that we considered to be grounded on constructive learning. The detailed and design processes are described below. Forty students were tested using pilot items in our instrument. After the pilot test, we modified the test items and then ran the experiment. Thirty-nine tenth grade students (15 − 16 years old) in Taipei city were required to complete a set of test items dealing with the states of matter: solid, liquid, and gas. The test took the students about 15 − 20 minutes to complete. These subjects had learned some concepts related to the three states of matter in the 8th and 9th grades along with fundamental concepts about particles. However, they were never taught or tested using dynamic representations of particles in school. The majority of them stated that they had never seen this type of dynamic test item before. 3. Instrument The development of the diagnostic materials involved several phases, and is described below. A. The First Phase: Interviewing 1. Research Design The tools used in the early stage of this study were mainly interviews, drawings, paper-and-pencil test items, and computerized test items. For this type of study, many researchers in science education believe that a drawing is a convincing way to illustrate what the students have learned in chemistry. However, this study intended to extend this approach to computerized simulation to investigate the students’ understanding of particulate theory. To accomplish this goal, we employed a two-tier testing technique proposed by Treagust (1995) to obtain the students’ knowledge structure by asking them to answer open-ended questions and make diagrams to show their mental images or representation of particles. The students were required to make drawings, use Styrofoam, and think aloud about their images of particles during the interviews. First, we To understand tenth graders’ preconceptions about the behaviors and structures of particles in three states (solid, liquid, and gas), we interviewed 10 students individually using open-ended questions. The students were required to draw graphs showing their mental images, use Styrofoam balls to represent the three states of particles, and think aloud while they were interviewed. B. The Second Phase: Paper-and-Pencil Test Responses to the interview questions were used to form multiple-choice items for a paper-and-pencil test. These items were considered to be student-oriented items that were different from traditional multiple choice test items. Once the items were constructed, an entire class of 40 students was tested. The students were asked to select − 92 − Dynamic Representations as Diagnosing Tools Fig. 1. Question 1-1 in the test. Fig. 3. Question 3-1 in the test: Which of the following graphs shows the atomic arrangement of a liquid vaporizing to form a gas in a closed container? Fig. 2. Question 2-1 in the test. the most appropriate answer to each question and then give explanations for their choices. The data obtained from the students were analyzed and developed into two-tier test items: the first tier for their image representations and the second tier for their explanations. C. The Third Phase: Development of Diagnostic Software Using Two-Tier Test Items Based on the drawings obtained from the initial interviews and the student responses from the paper-andpencil test, we developed a computerized test package focusing on the students’ mental models of particles. This computerized test package was specifically designed to be unlike the common static representations of particles. Rather, it dynamically revealed the characteristics of particles. Therefore, all the responses students could choose from were dynamic. In total, there were 12 test items divided into three sets. All three sets were intended to reveal students’ factual understanding and the reasons for their conceptions. The three sets are given below: (1-1-1) Which of the following graphs best represents the motion of particles in solid state at a particular temperature? Please click one. (1-1-2) The one you have chosen is shown below. Please explain your answer. (1-2) Is there anything between the atoms? Why? (1-3) If there is another solid metal that consists of the same materials at the same temperature, would the atoms be arranged in the same way? Why or why not? (2-1-1) Which of the following graphs shows the atomic arrangement of a solid melting to form a liquid (assuming that the volume remains constant)? Why? (2-1-2) Your choice is shown below. Please explain your answer. (2-2-1) Which of the following graphs best represents the movement of particles in a liquid? (2-2-2) Your choice is shown below. Please explain your answer. (3-1-1) Which of the following graphs shows the atomic arrangement of a liquid vaporizing to form a gas in a closed container? (3-1-2) Your choice is shown below. Please explain your answer. (3-2-1) Which of the following graphs best represents the movement of particles in a gas? (3-2-2) Your choice is shown below. Please explain your answer. − 93 − M.L. Chiu et al. Table 1. Average Scores of the Students on Items Related to Solid, Liquid, and Gas Concepts State Number of question mean s.d. solid 1-1 1-2 1-3 average 2-1 2-2 average 3-1 3-2 average 2.79 2.10 2.74 2.55 3.18 2.05 2.61 2.77 3.36 3.06 1.49 1.50 1.74 0.16 1.27 1.61 0.20 1.35 0.84 0.13 liquid gas Table 2. Correlation Coefficients for the Students with Respect to the Total Scores and the Solid, Liquid, and Gas Item Scores, Respectively Solid solid liquid gas Total 1.000 0.157 (0.339) 1.000 0.063 (0.702) .181 (.270) 0.738** (0.000) 0.687** Liquid Gas (1.000) (.000) .489** (.002) ** Correlation is significant at the 0.01 level (2-tailed). ( ) Standard deviation. student conceptions about particles. After conducting the paper-and-pencil test items with class A consisting of 40 students, we modified the test items and developed a software program designed to use dynamic representations of particles to test the students. To show the dynamic movements and structures of particles, we used FLASH, a computer application tool, to present particles’ motions in the three states. This application tool allowed students to make their own choices and then explain their selections. Once the program was tested and modified, two chemists from the Department of Chemistry reviewed it for external validity. Then, we modified the software again and tested it on 39 tenth graders in class B individually in a computer lab. Each student worked alone at his or her own computer. Both qualitative and quantitative data were collected. Although the responses from the first tier were quantitative data, they were based on qualitative interview data that could be considered to more authentically reflect of students’ understanding of particles. III. Results The following analysis has been based on three perspectives: statistical performance, mental models, and explanations of the states of matter. 1. Students’ Performance Fig. 4. Pictorial representations of students’ conceptions of the motion of particles. D. The Fourth Phase: Expert Validation After the prototype learning materials were developed, two professors from the Department of Chemistry of National Taiwan Normal University reviewed the software and gave very positive feedback. We also asked them to check the accuracy of the contents of the learning materials. The package was then modified according to their feedback. We also deleted choices from the package deemed inappropriate because they were chosen by no one or very few students. 4. Procedure As described in the previous sections, our main task was to develop cognitive-based test items to diagnose Table 1 shows the average scores of the students on items related to solid, liquid, and gas concepts. The average scores for solid, liquid, and gas were 2.55 (s.d. = 0.16), 2.61 (s.d. = 0.20), and 3.06 (s.d. = 0.13), respectively. After making pairwise comparisons (Least Significant Difference), we found that there were significant differences between solid and gas (p = 0.014), and between liquid and gas (p = 0.044). To our surprise, the students on average had the highest scores for particles in the gas state, which we considered to be more complex and abstract. Table 2 shows the correlation coefficients for the students on items related to solid, liquid, and gas concepts. The total scores were significantly correlated with the scores for the solid, liquid, and gas items; however, the solid, liquid, and gas item scores were not significantly correlated. Tables 3 and 4 show that although many of the students chose the correct figure (Item B in Fig. 1) to represent the motion of particles in the solid state, their explanations for their choice varied in terms of type and quality. Pictorial representations of their mental models are shown in Fig. 4. Tables 5 and 6 show the responses to Question 12, which asked, “Is there anything between the atoms?” Table 6 reveals that 9 out of 22 students, who believed that − 94 − Dynamic Representations as Diagnosing Tools Table 3. Responses to Question 1-1* Question 1-1: Which of the following graphs best represents the motion of particles in solid state at a particular temperature? Please click one. Choice Correct reasons Sub. No. A Vibrate all the time at the same place (Fig. 4(a)). Vibrate at the same place, but cannot be seen (Fig. 4(b)). 19 2 Choice Partially correct reasons Sub. No. Low temperature, low energy, vibrate little vibration (Fig. 4(b)). Low temperature, low energy, vibrate little vibration (Fig. 4(b)). Irregular action, very little vibration small (Fig. 4(b)). Irregular action, very little vibration small (Fig. 4(b)). Not in same direction (Fig. 4(a)). 4 1 2 1 1 Incorrect reason Sub. No. Still (Fig. 4(c)). Still (Fig. 4(c)). NA 6 1 1 B B A A B B Choice A B B *datum was missing. Table 4. Summary of the Correctness of Students’ Answers to Question 1-1* Atoms are motionless in solid state little vibration total Correct Partially correct Incorrect Total 2 3 6 11 19 21 6 9 2 8 27 38 Space exists between atoms Nothing exists among atoms Depends Total *One data was missing. Table 5. Responses to Question 1-2 Is there anything between the atoms? Yes No √ √ √ √ √ √ √ √ √ √ √ √ √ Correct or partially correct reasons With attractive force (Fig. 5(b)) Vacuum Partially correct reasons Electrons (Fig. 5(a)) Some force (Fig. 5(b)) No space to hold anything Connected with each other Others Incorrect reasons The atom is the smallest unit. Space Others Table 6. Summary of the Correctness of Students’ Answers to Question 1-2 Sub. No. 6 3 2 1 3 3 3 4 1 2 2 1 6 there was nothing between the atoms, also believed that of an attractive force existed between the atoms. The rest of the students (n = 13) believed that there was no space between the atoms. Correct Partially correct Incorrect Total 0 9 6 10 9 3 9 16 12 15 22 2 39 Question 1-3 tested a simple concept about whether or not another block of the same material (metal) would have the same atomic arrangement at the same temperature. Table 7 shows that a majority of the students believed that as long as the same metal was at the same temperature, it would have the same atomic arrangement. However, it was peculiar that several students believed that identical metal blocks at the same temperature would have different arrangements of atomic particles. Similar to Question 1-3, Question 2-1 (Fig. 2) asked the students to choose the picture that best represented the atomic arrangement of a liquid (Tables 9 and 10). Finally, Tables 11 and 12 show the students performance on questions regarding particles in a gas (Fig. 3). Figure 7 presents models of their understanding. Again, students who chose the same figure that best represented their conception of particulates in gas, often offered different explanations for their choices (Fig. 8). IV.Discussion and Concluding Remarks − 95 − From a previous study (Chiu, Chou, & Liu, 2002), M.L. Chiu et al. Table 7. Responses to Question 1-3 Question 1-3: If there is another solid metal that consists of the same material at the same temperature, would the atoms be arranged in the same way? Why or why not? Correct Choice Reason Sub. No. Yes Yes Yes Yes Same material, same arrangement (Fig. 6(a)). Same substance (Fig. 6(a)). Same temperature, same material. Other. 8 7 9 2 Choice Reason Sub. No. Yes Yes No The atomic arrangement is fixed (Fig. 6(a)). Low energy, stable. Different but similar (Fig. 6(c)). 1 1 1 Choice Reason Sub. No. No No No No Different arrangement and different spaces between atoms (Fig. 6(b)). Random (Fig. 6(d)). Different materials (Fig. 6(b)-(d)). Other. 2 2 2 2 Partially correct Incorrect Table 8. Summary of the Correctness of Students’ Answers to Question 1-3 Correct Same arrangement of atoms Different arrangement of atoms NA 26 0 0 26 Partially Incorrect Total correct 2 1 0 3 0 8 0 8 28 9 2 39 (a) (b) Fig. 5. The pictorial representations of “things” existing among particles. we knew that students tend to consider dynamic concepts of chemical equilibrium to be MATTER or event-like rather than constraint-based interaction, which is normally inconsistent with the students’ daily life experiences and understanding. In our current work, we found that the students believed that particles sink to the bottom of a container in solid state and float in the middle of the container when charging from the solid state to the liquid state. We speculate that the students think of the particles, as non-interacting substances. However, the particles are actually interacting with each other, a concept which seems to be poorly developed in students at the tenth grade level. This result would be consistent with what we found in our chemical equilibrium study and in other particle studies carried out by M.T.H. Chi and her colleagues (Chi, 1992; Chi, Slotta, & de Leeuw, 1994). (a) (b) (c) (d) Fig. 6. Pictorial representations of the atomic arrangement of the same metal at the same temperature. Several significant findings were obtained in this study. Question 2-1 gave five choices, each presenting a previous student misconception. Some students thought − 96 − Dynamic Representations as Diagnosing Tools Table 9. Responses to Question 2-1 Question 2-1: Which of the following graphs shows the atomic arrangement of a solid melting to form a liquid (assuming that the volume remains constant)? Why? Choice Correct reason Sub. No. C C C C Attractive force between atoms becomes weak; the atoms can vibrate (Fig. 7(a)). The distance between atoms in a liquid is larger than that in a solid (Fig. 7(b)). Same atoms but the arrangement of atoms is loose (Fig. 7(b)). The energy of atoms increases, the speed of vibration increases, making the distance larger (Fig. 7(b)). 11 8 3 2 Choice Partially correct reason Sub. No. C C C C E D A C Attraction force exists among molecules (Fig. 7(a)). Same number of atoms, increasing the volume (Fig. 7(b)). Same volume but different shape. The distance between atoms increases (Fig. 7(b)). Same number of atoms; since liquid can flow, it does not have a fixed shape (Fig. 7(b)). The electrons become active when the temperature increases, so the volume increases, too. Other. Other. 2 2 1 1 1 1 1 2 Choice Incorrect reason Sub. No. A The liquid sinks to the bottom of the container when it is melted. 1 Table 10. Summary of the Correctness of Students’ Answers to Question 2-1 A B C D E Total Correct Partially correct Incorrect Total 0 0 24 0 0 24 1 0 8 1 1 11 1 1 0 0 0 2 2 1 32 1 1 37 (a) (b) (c) (d) Fig. 7. Pictorial representations of the atomic arrangement in a liquid. that atoms sink to the bottom of a container (choice A) when something changes from the solid to the liquid state, or that some float on the surface (B). However, when the choices were incorporated into a dynamic software program, very few students chose these items. Instead, more students chose the option stating that atoms float in the middle of the container when changing from the solid to the liquid (regardless of the conservation of atoms). Similar results were also obtained for Questions 3-1 and 3-2. In our interviewing process, we found that the students had five types of mental models of the arrangement and motions of particles in a gas. However, the students tended to select the same answer (e.g., A for Question 3-1) to indicate their understanding. We wonder whether or not the different representations offered triggered different mental models held by the students, causing them to answer differently. In our analysis, we found that some students, even at the tenth grade, still believed that something exists between and among atoms. This result is consistent with Griffiths & Preston (1992). Also, we found that a common alternative conception about the static state of particles in a solid state was not revealed by our study as it has been in other research. Again, we speculate that the students had not only developed a more correct concepts of the particle action, but they also were able to differentiate between the movement of particles in liquid and solid states. Having examined the textbook used in the chemistry class at the tenth grade, we found that its pictorial representations were misleading, causing student misconceptions regarding how particles exist in different states. Due to the limitations of two-dimensional representations on paper, the dynamic interaction of the particles at different temperatures could not be depicted in the textbook, making it difficult for students to imagine how particles vibrate in different states, particularly in the solid state. This is consistent with the conclusion drawn by Stavy (1990). Research has shown that learning about the particulate nature of matter is important and necessary in chemistry (Krajcik, 1991). It is common to use multiple-choice paperand-pencil test items to study students’ scientific concepts. − 97 − M.L. Chiu et al. Table 11. Responses to Question 3-1 Choice Correct reason Sub. No. A A E A A E The total number of atoms stays constantis. Gas particles can move freely (Fig. 8). Attractive force decreases, so the particles can fill the entire container (Fig. 8). The distance between atoms increases (Fig. 8). The distance between atoms increases (Fig. 8). Attractive force decreases, so they can move more freely (Fig. 8). Attractive force decreases, so they can move freely (Fig. 8). 8 6 4 3 2 1 Choice Partially correct reason Sub. No. E A A A E E A The space between molecules is large (Fig. 8). Fills the entire container (Fig. 8). The molecules separate from each other more (Fig. 8). The molecules separate from each other more (Fig. 8). The heat energy makes the atoms move away from each other. The gas holds more energy than the liquid, so the interactive force among the atoms has less impact on the atoms. The space occupied by the gas becomes larger, but the total number of atoms remains constant (Fig. 8). 4 2 1 1 1 1 1 Choice Incorrect reason Sub. No. E E A E The restrained force disappears. The gas has no fixed volume or shape. Other. Other. 2 1 1 1 Table 12. Summary of the Correctness of Students’ Answers to Question 3-1 A B C D E Total Correct Partially correct Incorrect Total 19 0 0 0 5 24 4 0 0 0 6 10 1 0 0 0 4 5 24 0 0 0 15 39 Fig. 8. Pictorial representation of the atomic arrangement in a gas. methodology, the dynamic graphs also shed some light on the students’ mental representations of the particulate nature of matter. In this study, however, we made use of two-tier items to diagnose students’ conceptions of the particulate nature of matter based on their own points of view. We believe that it is more meaningful and valid to identify students’ understanding of particles by showing them simulated representations of particles. We also believe that the students chose pictorial presentations in a multiple-choice format similar to those they provided when interviewed using open-ended questions because the multiple-choice questions were designed based on the students’ original responses to the open-ended interview questions. The present study also suggests that although the students may have chosen the same answers to the open-ended and multiplechoice questions, they might provided completely different explanations to the answer. The second-tier explanations for each question revealed each student’s idiosyncratic thinking about the particulate nature of matter. Besides the Acknowledgment This work was made possible in part by Grant NSC 90-2511-S003-092 provided by the National Science Council, R.O.C. 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