Mental models of atomic structure concepts of 11th grade chemistry students

The results of the analysis of the emergence of the mental model of students in response to the question No.1 diagnostic test of atomic structure model (TASM-01) will be described here. The results of the analysis of students' answers to TASM-01 are illustrated in Figure 1 below.

Figure 1. Percentage of Students with Initial Mental Model on Specific Characteristics for Question TASM-01.

Based on the students' answers to the TASM_01 question (Figure 1), it can be said that students from three schools (with differing backgrounds) provide responses that are not different, resulting in the same initial mental model, namely "very bad or unformed" and "bad".

Figure 1 shows that the majority of high school students (> 67,5%) consider that the third stage is the process of physical change and only 5,62% who answered that the third stage is the process of chemical change. This means that students do not have sufficient understanding of the structure of atoms and molecules. However, students from school C (students who are in the company's industrial/agro-industry) have a better ability to distinguish the structure of atoms and molecules rather than students from school A (students who were in the neighborhood of employees and vendors). This is indicated by the responses of students better than students in schools located in the the provincial capital (School A) and near the provincial capital (school B: students in a farming environment). Students who are in the company's industrial/agro-industry (school C) can understand that the second and the fifth process are physical changes, while the third is a chemical change, but it is still not appropriate for explaining why the processes depicted in the diagram are the process of physical and chemical changes. Based on interviews found that students consider splitting diatomic molecule into monatomic molecules (2 separation handball) is a physical change to the analogy "paper torn into two parts" or "wood is broken."

The study provides information that grade 11 students, who have studied the structure of atoms, are still not able to read the submicroscopic diagram well enough to distinguish the structure of atoms and molecules, and also in recognizing the changes of molecules when turning into atoms, the change of compounds into elements, and changes in a substance that does not change the structure of the substance itself. It shows that the senior high school students' initial mental models in understanding the physics and chemical changes are still dominated by the macroscopic level.

Based on interviews found that students consider splitting diatomic molecule into monatomic molecules (2 separation hand ball) is a physical change to the analogy "paper torn into two parts" or "wood is broken." Results of interviews to three students (S1: Students from school A; S2: Students School B; and S3: Students from School C) the following:

R (Reviewer): Are you able to identify any changes that occur in each process shown by the question No.1? How is your analogy in answering these questions?

S1 : Yes, partly. I think the process of 1, 2, and 3, are physical processes, while 4 and 5 are chemical processes. Because I hesitate to read the images, I can hardly make an analogy.

S2 : No, so I did not answer the question 1, because the time in high school before, I have never seen pictures like that, explanation and questions were text-only with words. The pictures given puzzle me. Process 2 and 3 are physical processes. In the second process, itcircle do not change, only the colour of their partners are exchanged, while the third process, the ball remains blue-ball just split it, that had kept the breakaway coupling. Then I think, process 3 is as if we tore the paper into 2 parts or broken wood.

S3 : Yes, partly. I think in the 2 and 3 are the processes of change in physics, while the fifth is a chemical change. My understanding, that chemical changes like the ionic bonds, whereas the physical changes if there are more similar objects repel each other. For the second way: the pictures in pairs balls red and blue are not bound to secede only. While the process 3, is like a ball similar hand in hand. Similar balls will repel each other, so that the balls were split into two due to mutual repulsion. Ehmmm ... it was like we tear the paper or break the wood, so it breaks into two parts.

The results of interviews with three of the respondents indicate that students' mental models are not good. From the interview, it appears that students are not able to distinguish the structure of molecules and the atomic structure at the level of sub-microscopic. Students have difficulty in distinguishing between molecules and atoms when dealing with a visual representation of sub-microscopic images. This finding is consistent with the Park (2006) that students' mental models of chemical phenomena depend on the ability to distinguish between the sub-microscopic structure of molecules and atoms. Therefore, it is necessary strategies that are able to develop the ability to reason, interpret, and represent chemical phenomena well, so that students early mental model hybrid (Vosniadou & Brewer, 1992) can be established to reduce the conflict between the conceptual definition of experts, with the visual images that the students in the molecular structure at the sub-microscopic level.

The question on test number 2 (TASM-02) shows that students are still experiencing difficulty in making the transformation from a verbal representation to a visual representation regarding the nuclear model of the atom. The difficulty is caused by the lack of creative imagination being used by the senior high school students because they did not practice in the instruction that took place. According to students that the learning of chemistry that lasted so far was only done verbally, students were never trained with the visualization of atoms and molecules. The question on TASM-02 is the question of student understanding on the atomic structure model according to the core model.

The results of the analysis of students' answers to the TASM_02 test question showed that the majority of students are still not able to understand the atom core model, be they students from schools in cities or students from schools in areas far from cities. As TASM-01, the analysis of the students' answers to TASM-02 has a resemblance (Figure 2). These results indicate that students with their knowledge of chemistry they have learned and taught by teachers are still not able to perform the transformation of macroscopic (experimental phenomena Thomson, Goldstein, Chadwick, and Rutherford) for the sub-microscopic and symbolic phenomenon. Similar to TASM-01, an analysis of students' answers to questions TASM-02 shows that students from school C (students who are in the company's industrial/agro-industry) has the capability to provide a visual representation of the arrangement of atoms based on the theories of Thomson, Goldstein, Chadwick and Rutherford more better than students from school A (students who were in the neighborhood of employees and vendors) and students from school B (students in a farming environment)

Figure 2. Percentage of Students with Initial Mental Model on Specific Characteristics for Question TASM-02.

Based on questionnaires filled out by the students, it appears that a study on the concept of atomic structure implemented by teachers are not trained 'skills of interpretation and visual representation of the phenomenon of sub-microscopic particles in the atom, so students are not used to the visual representation of the particles in the atom. Students transform the phenomenon of visual to verbal or otherwise through the ability of creative imagination on the structure of the particles in atoms, then adjust the image sub-microscopic of parts of atoms, then the student is asked to write the arrangement symbolic of electrons, protons, and neutrons in the atom based on the visual image. The visual image that has made the students be very simple and most (43.82%) are unlikely to distinguish between the atomic model of Rutherford and Bohr atomic model. Students' mental models in response to questions TASM_02 showed that students had difficulty in making the transformation of chemical phenomena of submicroscopic to macroscopic and symbolic or otherwise.

The difficulties of the students in understanding the atomic theory (Thomson, Goldstein, Chadwick, and Rutherford) is due to students not involved with sub microscopic phenomena in the learning undertaken by their teachers at school. Nonetheless, students are able to put the symbols correctly. Where the symbol of chemistry is used to define a substance or represent a process or any changes that take place (Park, 2006). This finding appropriate studies before that the understanding of chemical concepts cannot be achieved only by involving rote verbal only, but also requires an understanding of the phenomenon of representation of the structure of sub-microscopic molecules or atoms (Coll & Treagust, 2003; Hilton & Nichols, 2011; Park, 2006). In this case, Coll (2008) found that the ability of learners to operate or use their mental models to explain the events that involved the use of representations of sub-microscopic very limited, so there is a need to train learners in interpreting the phenomenon of sub-microscopic through instruction involves three levels of chemical phenomena.

Based on interviews found that the difficulties faced by such students are more due to students not getting experience in making an interpretation of the electron orbit according to Bohr. On interviews appears that students from school A and school B had difficulty in explaining, describing, and interpreting visual images of the atom and its structure is based on the theory of Thomson and Rutherford. While students from school C has more ability in explaining and interpreting visual images. The interview results showed that students had difficulty in maintaining his understanding of the phenomenon of electrons in atoms through learning only made orally, so the mental model does not form properly. These results also indicate that students have been able to image the atomic structure sub-micro in a simple manner, namely by means of symbols, but the difficulty in translating the verbal image.

Associated with the understanding of the electron orbit according to Bohr poured into question TASM_03, where students are asked to make the transformation from verbal to visual and symbolic representation or otherwise regarding the determination of electron orbit according to Bohr then create a visual image through an energy level diagram.

The result of the analysis of student answers to the TASM-03 question is illustrated in Figure 3 below. Analysis of the students' answers to the TASM-03 question showed similar results with the results of the analysis of TASM-01.

Figure 3. Percentage of Students with Initial Mental Model on Specific Characteristics for Question TASM-03.

These results indicate that the 11th graders who have studied the topic of atomic structure are still having trouble in making the transformation phenomenon of verbal to the visual phenomena of the atomic theory of Bohr. However, the percentage of students from schools located far from the provincial capital, which has high mental models, is higher than the percentage of students who were in the neighborhood of employees and vendors, and students in a farming environment (Figure 3). Thus, it can be said that the majority of students have difficulty in representing the sub-microscopic phenomena of the Bohr atomic theory, whether students from schools in the provincial capital, as well as students from schools far from the provincial capitals. Interviews showed that the difficulties faced by such students is more due to students not getting experience in making an interpretation of the electron orbit according to Bohr. Student difficulties in representing the sub-microscopic phenomena of the Bohr atomic model can be seen from the examples of student answers the following:

S1: student from School A

S2: student from school B

S3: student from school C

Overall, for all the students from the three schools of different categories, the analysis shows that the majority of students (> 70.00%) have a mental model in understanding the Bohr orbit is within the category of "very bad" and "bad", or the characteristics of mental models "unformed" and "intermediate 1.

Analysis of the students' answers to questions TASM-03 showed that some students (16.85% students in a farming environment and 14.61% students who were in the neighborhood of employees and vendors, and students who are in the company's industrial/agro-industry) is actually able to interpret and make the transformation to a particular phenomenon, but there are a misunderstanding in describing the atomic model of fluorine and sodium. Students from school A is not able to represent the Bohr model of the atom fluorine and sodium through the visualization of images, where the arrangement of electrons is placed entirely inside the circle is created. The image is contrary to the theory of the Bohr atomic model. Furthermore, students from school B and students from schools C to draw models of fluorine and sodium are in accordance with the Bohr model, but there is a mistake in preparing the skin of electrons in atoms. Before they make the visualization of images, students draw up electrons in the s and p orbitals in advance. This is not the Bohr model, but the model of wave mechanics.

Based on the analysis of students 'answers, it seems that the students' answers to questions about the atomic model of Bohr have disturbed with mechanical model of waves, namely by creating electron configuration using a system of orbital of s, p, d, f, whereas what is required is the Bohr model are familiar with the term orbital. However, students who are in the company's industrial/agro-industry has the more precise answer than students from both schools the other. As a result of an error in interpreting the arrangement of electrons in an atom, the students' answers to questions TASM-03 produces the mental model with the category of "very bad" and "bad." The results of interviews with three students showed that the ability to make the interpretation in distinguishing Bohr model of the atom and the wave mechanics model visually is not trained in the instruction by the teacher. According to students, the atomic model of wave mechanics was not studied in detail as they learn. During the study the atomic structure of matter, the students only learn verbally, students are not given the experience in interpreting Bohr electron orbit and the energy that accompanies the movement of the electron in its path, nor trained in understanding how to model the mechanical waves in explaining the position and behavior of electrons in atoms.