Development of Chemical Concepts by the Use of Molecular Computer Animations
Abstract
A central issue in chemistry education is the relation between real world and the molecular or nanoscopic world. Beginning students in chemistry could better understand chemistry and apply their chemistry understanding to solve problems if they were able to make appropriate connections between these worlds. It is supposed that animations can be used in chemistry education so that students get a better knowledge of molecular processes by making better relations between the macroscopic and the nanoscopic world.
Seventy-three 9th grade students from one high school were assigned to three groups. Group1 students received instruction on paper about the melting of ice and the dissolving of salt. The students from Group2 were shown animations about these processes and were required to complete assignments and perform a number of tasks for which they had to observe the animations (goal-oriented observation). The students in Group3 were asked to make animations by themselves.
Before and after instruction the students made a test about the melting of ice and the dissolving of salt in water. The same test was used before and after the lessons; it included questions about the macroscopic phenomena, and the students had to make drawings of the nanoscopic world to explain the phenomena. After the posttest the students were asked how they appreciated the instruction compared to their regular instruction at school.
All three forms of instruction showed higher scores on the posttest than on the pretest. The students from Group 2 (goal-oriented observation) outperformed the students of the other two groups. They also appreciated their instruction more than the students of Group 1 and Group 3. This indicates that the best way to teach the molecular processes melting of ice and dissolving of salt is to direct the students' observation to the critical features of the molecular animations and require them to complete assignments about the molecular processes.
1Introduction
Chemistry explains many phenomena in the real world, the world as we observe it, with the abstract concepts of atoms, molecules and ions. In order to do so, chemists, in their cognitive processes, switch easily between the real world and the nanoscopic or molecular world of atoms, molecules and ions. Furthermore, chemists are used to think in chemical formulas and equations, which form the symbolic world of chemistry. Many chemists automatically choose the representation that is useful at that moment. For chemists these three worlds are integrated: when thinking of water, chemists have in mind the colorless liquid, the formula H2O, and some molecular image at the same time.
Chemistry teaching and learning are complex, because conceptual understanding requires the learner to link several modes of representing matter and the interactions that matter undergoes during physical and chemical processes. Beginning students in chemistry often lack the ability to switch easily between the three chemical worlds. Observations are made in the real or macroscopic world, and explanations (theories) and predictions that students are supposed to understand are in the nanoscopic world. The explanations and predictions are also represented in the symbolic world. Students could probably get a more complete understanding and will be more able to solve problems if they would make better connections between these worlds (Gabel, 1998; Herron, 1996). A starting point in curriculum development is the arrangement of concepts and theories from simple to complex, from concrete to abstract, and from known to unknown. Substances that are known to students can have a complex symbolic representation (rubber, glass, wood, concrete, stone, paper, plastics). Therefore these materials are not suited as a starting point for chemistry education, and chemistry teachers and curriculum developers have to use substances that are more unfamiliar to the students.
Because atoms, molecules and ions are abstract entities that are too small to be seen, it is difficult to imagine what they will look like. Many authors therefore argue that visualization enhances the deep understanding of chemical concepts (Barnea & Dori, 1996; Sanger & Badger, 2001; Wu, Krajcik & Soloway, 2001), and many chemistry teachers use illustrations of the molecular world and molecular building kits in their lessons in order to make the abstract nanoscopic world more concrete to their students. A chemistry teacher will confront students with models of atoms, molecules and ions. These models can be drawings on paper (in the textbook) or on blackboard, three-dimensional models of wood or plastic, models on a computer screen, and so on. In a chemical reaction substances disappear and new substances appear, because bonds between atoms and ions are broken and new bonds are formed. Properties of substances are determined by the bonding between atoms, molecules and ions, and the kind of structures formed (Johnson, 2000). The change of molecules during a chemical reaction can be shown in icons (e.g. in several stages of the reaction), or in an animation. Students will first develop concepts about the state and structure of substances, and then about the change of matter.
Students will have a mental model of both particles and the process in which these particles change. These mental models will develop during instruction. One goal of instruction is the development of appropriate mental models, equivalent to conceptual models that are accepted by the scientific community (Greca & Moreira, 2000; Seel, 2003; Seel, 2004). It is difficult to find out how the students’ mental models look like. One way is to let students make sketches of their mental models (Greca & Moreira) and let them explain their drawings. This method of investigation is done by several authors (Ardac & Akaygum, 2004; Chittleborough, Treagust & Mocerino, 2002; Coll & Treagust, 2003; Harrison & Treagust, 1996; Harrison & Treagust, 2000; Vermaat, 2002; Vermaat, Kramers-Pals & Schank, 2003; Williamson, Huffman & Peck, 2004). Other ways are to let students build models of molecules with a molecular building kit, or to let them make a computer animation, but these methods take more time.
In order to develop their mental models students have to learn, and for this learning instruction is needed. There are different theories how this instruction can be designed. In instruction for problem-based learning the process of growth of knowledge is characterized by problems that students have to solve about the objects of a domain (Dijkstra, 2004; Dijkstra, in press). Students will have to develop mental models of an object, of the process, and of the new or changed object or objects. Then students will develop a line of reasoning. This starts with a hypothesis, which will become a part of a theory if the hypothesis is confirmed continually.
In regular chemistry education the problems are often questions students have to answer after they have read some texts. Students have to repeat a text passage in their own words, gave an explanation, complete a reaction equation or draw substances or atoms, molecules and/or ions, and so on. Students will make mistakes while answering questions, they should get feedback form the teacher, and this feedback will lead to knowledge development.
When students can see computer animations, they should complete assignments and perform tasks for which they have to look at the animations. The teacher or instructional program should pinpoint to relevant features of the process (Weiss, Knowlton & Morrison, 2002). Just as in regular chemistry education, students will develop their knowledge from the feedback they get on their answers, both from the teacher and from matter itself.
Another way to develop knowledge is to construct animations, for which students have to apply knowledge they acquired from the textbook or from the teacher. Probably students will make mistakes while constructing these animations. Feedback on these mistakes will lead to knowledge development. If students have to make animations by themselves, they will have to think about the course of the nanoscopic processes and predict what will happen. They will get feedback on what they constructed and enrich their knowledge from that. These students most likely will develop the adequately corresponding mental images, which means they will be in accordance with scientifically accepted models.
Although animations seems to be a plausible tool for teaching and learning chemistry, little is known about the way they can be used effectively in chemistry education. Just showing animations will probably not be effective. If students get instruction on paper, including drawings of molecular processes, they may develop rather weak mental images of these processes, which will not correspond to the scientific models. There is no argument that these images will possibly become more accurate if the students just look at animations. So far there is little or no research on instructional designs of what is remembered and understood after observing animations. In a study by Ardac & Akaygum (2004) two groups of students were compared. Students from the treatment group received multimedia-based instruction that emphasized molecular representations. These students significantly outperformed students from a regular instruction group in a pretest/posttest experimental design, especially for questions in which the students had to represent matter at the particle level. The authors did not know if the improvement was due to the emphasis on molecular representations in the treatment group, and to the use of multi-media.
The purpose of this study is to investigate if the students' construction of molecular computer animations will positively support the explanations of molecular processes (in terms of scientifically accepted models). Possibly these students will outperform students who observe animations or study icons in textbooks. A second goal of this study is to investigate how students appreciated the use of molecular animations compared to their regular instruction they receive at school.
2Method
2.1Participants
Seventy-three 9th grade students from one high school participated in this study. These students were randomly assigned to three groups of participants. The students received instruction about the processes of ‘melting of ice’ and ‘dissolving of salt’. Group1, control condition, consisted out of 23 students (10 female, 13 male). The students in this group received instruction on paper. Group2, goal-oriented observation condition, consisted of 26 students (10 female, 16 male). These students observed animations of the processes and made assignments about it. Group 3, construct condition, consisted of 24 students (9 female, 15 male). They were asked to make animations by themselves, and had to answer questions during the constructing.
2.2Materials
A plenary lesson was given that started with a demonstration that ice floats on water, whereas in a mixture of solid and liquid olive oil the solid part is at the bottom of the flask. After that they were shown Figure1, familiar models of a solid and a liquid that is shown in many Dutch textbooks (Camps, Pieren, Scheffers-Sap, Scholte & Vroemen, 2002; De Valk & Ousen, 2003; Hogenbirk, Jager, Kabel-van den Brand & Walstra, 1999; Pieren, Scholte, Smilde, Vroemen & Davids, 1989). The students had to tell how many molecules there are in the solid and in the liquid. Then the students had to tell if, according to this model, the solid would be denser than the liquid, or the other way round. All students agreed that the solid would be denser, according to this model, so that the model had to be reversed.
Figure 1.Models of a solid and a liquid, as taught in Dutch schoolbooks
In the second demonstration the students had to foretell if solid salt (the demonstrator used a large lump of rock salt or sodium chloride, NaCl) and distilled water are conductors or insulators for an electric current. All students agreed that both materials are insulators, and it was demonstrated that this is the case indeed. Next a portion of salt was dissolved in water, and the students were asked if the solution would be a conductor or insulator. All students expected the solution to be a conductor, and it was demonstrated that this is true.
At last the students were told that they would get an instruction to explain the two phenomena: (a) ice floats on water, whereas in a mixture of solid and liquid olive oil the situation is the opposite, and (b) solid salt and distilled water are insulators, whereas a mixture of salt and water is a conductor. This instruction was done in three different ways, and in all three ways the relation between the nanoscopic and macroscopic world was emphasized.
Group 1 (control condition)
The instruction was based on the textbooks that the students would use in the 10th grade (Van Antwerpen, Bouma, Le Fèvre, Van Schravendijk, Schouten, Van Steeg & Termaat, 1998a and 1998b). Relevant parts of these books were copied and complemented with extra assignments and pictures. These students only got instruction on paper; no animations were used.
For the first phenomenon (ice floats on water, whereas in a mixture of solid and liquid oil or fat the situation is the opposite) the students were shown pictures of a mixture of ice and water and a mixture of solid and liquid fat for deep frying (Figure 2). It was pointed out to the students that in the mixture of ice and water the solid is at the top, whereas in the mixture of solid and liquid fat the solid is at the bottom. Next the dipole character of the water molecule and the hydrogen bond were explained, and a drawing of the hexagonal structure of ice was shown (Figure 3). The students had to (a) draw four water molecules with hydrogen bonds between them, (b) explain that ethanol also forms hydrogen bonds, (c) draw hydrogen bonds between a water molecule and an ethanol molecule, and (d) explain that ice floats on water, whereas in fat the solid phase sinks to the bottom.
Figure 2. In a mixture of solid and liquid water (left) the solid floats; in a mixture of solid and liquid fat for deep frying (right) the solid sinks (Van Antwerpen et al, 1998a, p. 117).
Figure 3.Illustrations from the instruction for Group 1 (control condition).
Upper part: water molecule as a dipole (spacefilling model and structural formula), and a hydrogen bond between two water molecules.
Lower part: the hexagonal structure of ice and hydrogen bonds between water molecules. The illustrations in the lower part are from the textbook used by this school (Van Antwerpen et al, 1998a, p. 116).
The instruction for the second phenomenon (solid salt and distilled water are insulators, whereas a mixture of salt and water is a conductor) started with a copy from the textbook in which the concept ion was explained. The copy showed a photo of an electrical circuit (like the right one in Appendix 1) with the following caption:
“A solution of sugar does not conduct an electrical current, solutions of salt conduct an electrical current. Thus solutions of salts contain free moving particles (ions).” (Van Antwerpen et al, 1998a, p. 73.)
The illustration from the textbook was accompanied by the following text:
Solid table salt does not conduct an electrical current. A solution of table salt in water does conduct an electrical current.
Copper chloride behaves in the same way. During electrolysis[1] of a solution of copper chloride, copper is deposited at the negative pole. An electrical current is the motion of electrically charged particles. We assume that the solution contains positive copper particles, which are attracted by the negative pole. There they are converted into copper atoms.
Bubbles develop at the positive pole. There you smell chlorine. The chlorine particles in the solution are negatively charged, and are attracted by the positive pole. There they are converted to chlorine atoms, which form molecules Cl2.(Van Antwerpen et al, 1998a, p. 73.)
The charged particles are called ions. They are formed because an atom has gained or lost electrons[2]:
A positive ion is an atom that has lost electrons.
A negative ion is an atom that has gained electrons.
In positive ions there are less electrons, in negative ions there are more electrons than protons.
The text from the textbook explicitly gave the explanation for this phenomenon:
“A solid salt does not conduct an electric current. A solution of salt in water and a molten salt do conduct an electric current. Electric current is the motion of electrically charged particles. In a solid salt all the ions are immobile. Then an electric current is not possible. In the solution and in the molten state the ions are mobile; therefore an electric current is possible.” (Van Antwerpen et al, 1998a, p. 97.)
The size of the ions was not mentioned in the textbook, and the students were provided with the information in Table 1.
Table 1Information about chlorine and sodium.
Name / Symbol / Atomic radius / Ionic radius / Ionic chargechlorine / Cl / 180 / 181 / 1–
sodium / Na / 186 / 98 / 1+
radius in pm, 1 pm = 10–12 m
The students had to (a) explain how many electrons a sodium respectively a chloride atom had to gain or to loose in order to become an ion, (b) explain how many chloride ions there will be in table salt for every sodium ion, (c) sketch the way they thought sodium and chloride ions are positioned in solid salt, and (d) draw a sodium and a chloride ion surrounded by water molecules. The instructor had to control these drawings.
Group 2 (goal-oriented observation condition)
The students of this group were shown the six molecular animations, described in Table 2, and they had to make assignments about these animations. So these students were provided with a conceptual model, which they had to internalize (Seel, 2004).
Table 2The six molecular animations shown to the students of Group 2 (goal-oriented observation condition).
Animation / Name / Description1 / Ice melting / A three-dimensional animation about the melting of ice (Figure 4) with spacefilling models for the watermolecules.
2 / Ice melting / A two-dimensional, more opened out animation (Figure 5), which showed clearly the change in volume when ice melts.
3 / Solid table salt / A lattice of little gray spheres (representing sodium ions) and larger green spheres (representing chloride ions). The sodium and chloride ions stay at their place, they only vibrate.
4 / Dissolving of table salt / First a small crystal of table salt is shown, then water is added and the water molecules can be seen as they pull out the ions one by one. First a chloride ion is pulled out (Figure 6, left), and then a sodium ion (Figure 6, right).
5 / Hydrated chloride ion / A chloride surrounded by six water molecules. The slightly positive hydrogen side of the water molecules is pointed at the negative chloride ion.
6 / Hydrated sodium ion / A sodium ion surrounded by six water molecules. The slightly negative oxygen side of the water molecules is pointed at the positive sodium ion.
Animation 2 was made by the author, the other five were made by R. Tasker of the University of Western Sydney, Australia (Tasker, Chia, Bucat & Sleet, 1996; see also