Article

UniServe Science News Volume 9 March 1998










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The VisChem Project: Molecular Level Animations in Chemistry - Potential and Caution

Roy Tasker,
r.tasker@nepean.uws.edu.au,
University of Western Sydney Nepean

Introduction

This paper shows how multimedia can provide a structured approach to the 'thinking levels' of chemistry - the laboratory, molecular, and symbolic levels. In particular, computer animations offer the potential to portray the dynamic 3D molecular level more accurately than static 2D diagrams in textbooks, or static physical models (e.g. ball & stick). The article concludes with a warning about misleading molecular animations, published on CD supplements to some leading textbooks, with their potential to generate serious and deeply embedded misconceptions at this crucial thinking level.

Educational research into practice

A rich understanding of chemistry involves being able to link what one sees substances doing in the laboratory, to what one imagines is happening within these substances at the invisible molecular/ionic level. Only then can these ideas be communicated meaningfully using abstract symbolism (e.g. chemical formulas), terminology and mathematics. Johnstone1 refers to the three levels as the macro, sub-micro, and symbolic, and pictures them at the corners of a triangle. Thinking in chemistry is then likened to "moving between a series of points within the triangle, depending on the proportion of the three levels at any one time".

Figure 1.
Figure 1. Ice melting and the three 'thinking levels' - the symbolic (chemical equation), macro or laboratory (ice melting in beaker), and sub-micro or molecular (frames from an animation2)

Due to a shortage of high quality resources that portray the molecular level most chemistry teaching occurs at the laboratory and symbolic levels, in the hope that mental models of the molecular world will 'develop naturally'. Students are therefore left to develop these models from the static, often oversimplified two-dimensional diagrams in textbooks, or static, often confusing ball and stick models, or from their own imagination. However, there is convincing evidence3 that many student difficulties and misconceptions in chemistry stem from inadequate or inaccurate molecular models.

Computer animations - the potential to portray the molecular world

In the VisChem project2 a team of chemical educators is producing multimedia resources in video and CD formats to explicitly link the molecular, laboratory, and symbolic levels. The most novel resources are a series of computer generated animations which portray substances at the level of molecules, atoms and ions in the solid, liquid, and gaseous states; during phase changes (e.g. melting); and when they react together.

Great care has been taken in the representation of molecular structures and processes because research by Ben-Zvi4 and others has indicated that misconceptions can be generated easily, and perpetuated, with poorly drawn images.

Visualising the invisible molecular world to generate mental models requires imagination. For example, the speed of atomic and molecular movements, and the uncertain (non-Newtonian) nature of electrons in atoms, require substantial 'artistic license' to enable the structure and collisions at this level to be represented. For this reason students need to be constantly reminded that these animations are only 'models' of reality.

Animations can show the multiparticle nature of chemical reactions. For example, the laboratory observation of silver crystals growing on the surface of copper metal (Figure 2) are hardly consistent with the misleading diagram, often found in textbooks, of one copper atom donating an electron to each of two silver ions. An animation can show reduction of many silver ions on the copper surface, with concomitant release of many copper(II) ions, in a two to one ratio (Figure 3).

Figure 2.
Figure 2. Silver crystals form on the surface of copper metal as the solution gradually becomes blue.
Figure 3.
Figure 3. Frame from a VisChem animation showing reduction of silver ions to silver atoms, with the release of copper(II) ions.

Students need a refined model of hydrated ions in ionic solutions. The exchange of water molecules around the ions (as an introduction to formation of complex ions), the occasional formation of ion pairs (as an introduction to precipitation), and the migration of ions in the solvent are important images (Figure 4).

Figure 4.
Figure 4. A frame from a VisChem animation portraying a hydrated copper(II) ion about to collide with a hydrated nitrate ion in a 1M copper(II) nitrate solution.

A 'feeling' for ion concentration can be gained by 'looking into' the solution when most of the solvent molecules are 'removed' (Figure 5).

Figure 5.
Figure 5. A frame from the same animation with most of the solvent water molecules 'made invisible'. Hydrated anions and cations can be seen in the background.

The separation of ions by an average of three water molecules in a one molar solution conveys a concrete image of an otherwise abstract concentration unit.

Figure 6.
Figure 6. A frame of the VisChem animation which attempts to visualise gaseous water molecules 'pushing back' the walls of a bubble in boiling water.

Animations of the molecular world can stimulate the imagination, bringing a new dimension to learning chemistry. What is it like inside a bubble of boiling water (Figure 6), or at the surface of silver chloride as it precipitates (Figure 7)?

Figure 7.
Figure 7. A frame from another animation which depicts the precipitation of silver chloride after mixing solutions of sodium chloride and silver nitrate.

Analysis of an evaluation pre-test/post-test survey5 on the VisChem video The Molecular World of Water: Let's look into it, involving 21 educators and 160 students at both secondary and tertiary levels around Australia, was encouraging. The responses from students indicated that after a single viewing of this video they corrected their misconceptions and/or enriched their understanding. For example, after 61% of university students communicated the misconception that bubbles of boiling water contain air, only 25% gave this incorrect response after having viewed the video which included the animation described in Figure 6.

However, our work with students in small group interviews has also highlighted the potential for new misconceptions to be generated by some students from VisChem animations. For example, two students were curious about the reasons why the water molecules appeared to be 'carrying the silver chloride ion clusters' towards the growing silver chloride crystal. This unintentional impression was communicated by not showing sufficient exchange of hydrating water molecules around the cluster as it migrated towards the lattice.

Figure 8.
Figure 8. Frame from a VisChem animation showing the 'tug-of-war' for a proton on an iron(III) bound water molecule with a solvent molecule.

Many molecular processes involve a competition between competing forces. An example is the 'tug-of-war' competition for a proton on an iron(III) bound water molecule with a solvent molecule (Figure 8), and between lattice forces and ion-dipole interactions when sodium chloride dissolves in water (Figure 9).

Figure 9.
Figure 9. Frame from a VisChem animation showing the hydration of a sodium ion on the surface of sodium chloride despite strong attractive forces from the rest of the lattice.

Misleading animations

Unfortunately, there is a wide range of quality in molecular animations published internationally, and available on video, CD or over the Net. Compare the frame in Figure 10 below from one animation with Figure 9. They both attempt to portray the same process - NaCl dissolving in water. What messages are communicated by these images? Each animation conveys implicit and explicit information.

Figure 10.
Figure 10. Frame from an animation depicting NaCl dissolving (from Chemistry: Interactive, the CD supplement for Ebbing's General Chemistry, 5th Ed).

The animation in Figure 10 suggests that:

  • water molecules in the liquid state are widely separated; and
  • solid sodium chloride is composed of ions separated from each other by 'stick' bonds. This image is reinforced by the image of a water molecule 'passing through' the structure (sic!) to hydrate an ion, and by the space left when an ion, with its 'sticks', is removed from the lattice.

In contrast the VisChem animation in Figure 4 portrays:

  • water molecules in the liquid state as much closer together; and
  • solid sodium chloride as composed of ions, constantly vibrating, and closely packed together.

Another example of a misleading animation is represented by the frames in Figures 11 and 12. This animation is supposed to portray the reaction occuring when aqueous solutions of hydrochloric acid and sodium chloride are mixed. Figure 11 shows distinct HCl molecules in solution shortly before reaction with water molecules!

Figure 11.
Figure 11. Frame from an animation depicting hydrochloric acid which shows HCl molecules moving amongst water molecules, shortly before reacting with them!

Figure 12 shows NaOH 'molecules' being added in a drop of solution. Animations such as these reinforce the misconception that 'molecular' formulas for strong electrolytes, such as:

       HCl(aq)
and 'molecular equations' such as:
       HCl   +   NaOH   --->   H2O   +   NaCl
actually describe the species and processes occurring at the molecular/ionic level. Little wonder students have trouble with understanding electrolytes, and concentrations of ions in solution!

Figure 12.
Figure 12. Later frame from the same animation, just before a drop of sodium hydroxide solution, containing NaOH ion pairs, is added from a tube above. (Animation from Chemistry: Interactive, the CD supplement for Ebbing's General Chemistry, 5th Ed.)

The above animation also clearly illustrates the problem of mixing the laboratory and molecular levels in imagery. Could students develop the idea that a drop of water contains only a few ionic species? Could students develop the image of water composed of water molecules surrounded by some other 'watery matter' indicated by the grey background? Questions such as these are the focus of action research conducted in the VisChem project.

Conclusion

In the new millenium most information will be communicated using computer generated multimedia. We need to ensure that the same high academic standards we demand from text-based information are applied to visual information, which is arguably more effective in conceptual change, for better or worse.

References

  1. Johnstone, AH. (1991). Thinking about Thinking. International Newsletter on Chemical Education, 36, 7-11.
  2. animation from the VisChem project - see VisChem Web page - www.nepean.uws.edu.au/science/vischem/
  3. Lijnse PL, Licht P, Waarlo AJ and de Vos W (Eds.) (1990) Relating Macroscopic Phenomena to Microscopic Particles. Proceedings of Conference at Utrecht Centre for Science and Mathematics Education, University of Utrecht, and references therein.
  4. Ben-Zvi, R, Eylon, B and Silberstein, J. (1988). Theories, Principles and Laws. Education in Chemistry May, 89-92; Ben-Zvi, R, Eylon, B and Silberstein, J. (1987). Students Visualisation of a Chemical Reaction. Education in Chemistry July, 117-120.
  5. Tasker RF, Bucat R, Sleet R, and Chia W. (1998) Research into Practice: Improving Students' Imagery in Chemistry Manuscript in preparation.

Review of VisChem: Visualising the Molecular World

Roy Tasker
School of Science
University of Western Sydney Nepean
r.tasker@nepean.uws.edu.au
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UniServe Science News Volume 9 March 1998

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