Levels of representation

To recognize the different levels of representation of biochemical reactions To understand metabolic reaction networks To know the principles of retrosynthetic analysis To understand the disconnection approach To become familiar with synthesis design systems... 

Table 1 Words/phrases used for the three levels of representation...

Our interpretation of the finding from the study is that even within a single level of representation, i.e. sub-microscopic, some students were unable to translate between different modes of representation. In this case, there was evidence that students were unable to translate their verbal mode of understanding into the diagrammatic mode (or visual mode). If the translation between different modes within the same level is problematic, it would be very challenging when students are required to smoothly mentally move about and link all the three - the macro, the sub-microscopic and symbolic levels - of chemical phenomena. 

This chapter considers the nature of the symbolic level of representation in chemical education. It begins by suggesting why the use of symbolic representation in com-... 

Teaching Chemistry with the Symbolic Level of Representation... 

When students do make an attempt to relate between the three levels of representation, several unexpected trends in their reasoning are revealed. In the majority of explanations given by students about chemical reactions in a review imdertaken by Andersson (1986), there was a clear extrapolation of physical attributes and changes from the macroscopic world to the particle or submicroscopic one. So, when wood bums, wood molecules are also said to bum. If metallic copper is bright reddish-brown, atoms of copper are also imagined to be reddish-brown in colour (Ben-Zvi, Eylon, Silberstein, 1986). One reason for such extrapolation of physical attributes of substances to the particulate level is the tendency of students to assume that the atoms, ions and molecules in a substance are veiy small portions of the continuous substance. 

The extrapolation of physical attributes of substances to the submicroscopic level of representation was evident when students explained the changes in the displacement reaction between zinc powder and aqueous copper(II) sulphate. The decrease in intensity of the blue colour of the solution was attributed by 31% of students to the removal of blue individual Cu + ions from aqueous solution. The suggestion that individual Cu + ions (the submicroscopic level) are blue may be indicative of the extrapolation of the blue colour of the aqueous copper(II) sulphate (the macroscopic level) to the colour of individual Cu + ions (the submicroscopic level). Thirty-one percent of students also suggested that reddish-brown, insoluble individual atoms of copper were produced in this chemical reaction, again suggesting extrapolation of the bulk properties of copper, i.e., being reddish-brown and insolnble in water (the macroscopic level), to individual copper atoms having these properties (the snbmicroscopic level). 

First, teachers need to be made aware of the need to place greater emphasis on the purposeful use of multiple levels of representation when describing and explaining chemical phenomena during classroom instraction. All too often teachers take for granted that students are able to switch back and forth with ease between different levels of representation. The findings of this study have shown that students competence in the use of the triplet relationship to describe and explain chemical reactions was enhanced as a result of the instraction. 

Chandrasegaran, A. L. (2004). Diagnostic assessment of secondary students use of three levels of representation to explain simple chemical reactions. Unpublished doctoral dissertation, Curtin University of Technology, Perth, Australia. 

Chandrasegaran, A. L., Treagust, D. F., Mocerino, M. (2007). The development of a two-tier multiple-choice diagnostic instrument for evaluating secondary school students ability to describe and explain chemical reactions using multiple levels of representation. Chemistry Education Research and Practice, 8(3), 293-307. 

Table 8.1 Description of the rusting of iron at each level of chemical representation of matter Level of Representation...

This diagram may appear trivial to the expert chemist but for a novice it contains much information about the chemical reaction at both the sub-micro and symbolic levels presented in multiple representational formats. Unless teachers are explicit in their use of these representations it is umealistic to assume that students would develop the same ability to choose an appropriate representation for a given process. It is possible that students can use and understand the representations without being able to see how they are related. Several authors (Hinton and Nakhleh, 1999 Kozma and Russell, 1997 Nurrenbem and Pickering, 1987) suggest that students are made aware of all three levels of representations and given opportunities to use them in solving problems. 

Sub-micro representations are used extensively in teaching the mole concept, stoichiometiy, solubihty and chemical equilibrium at UCT. Having students draw and annotate chemical diagrams representing chemical phenomena at the sub-micro level can provide some insight into their understanding of chemistiy at the macro level. The following examples are typical of the questions used to probe links between the sub-micro and symbohc levels of representations as part of the assessment practice for this course. For example, students were asked to balance the equation shown in Fig. 8.7. 

Chittleborough, G. D., Treagust, D. E. (2008). Correct interpretation of ehemieal diagrams requires transforming from one level of representation to another. Research in Science Education, 38(4), 463 82. 

The capacity to mentally translate a given model between the modes and submodes and between the levels of representation in which it can be depicted. In so... 

In this chapter, we present an attempt to put these ideas into practice that has three components. First, we use a Model of Modelling , an external representation of the mental processes that we postulate to be undergone as a person forms a model. Second, this model is exemplified by its apphcation to the design of a teaching sequence about a key topic in chemistry, the imderstanding of which requires fluency of mental movement between the three levels of representation. Lastly, this application is implemented in such a way that the processes of students thought taking place can be monitored. 

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