Improving Representational Competence in Chemistry with Model-Based Feedback

Improving Representational Competence in Chemistry with Model-Based Feedback Shamin Padalkar (shamin.padalkar@psych.ucsb.edu) Mary Hegarty (mary.hegarty@psych.ucsb.edu) Department of Psychological & Brain Sciences, University of California, Santa Barbara Santa Barbara, CA 93106 USA Abstract Diagrams Used in this Study Representational competence is an important component of learning Organic Chemistry. However, students are seen to be incompetent in translating from one kind of molecular diagram to another. An instructional method informed by spatial cognition research was designed and administered individually. The instruction involved having students check their solutions by attempting to match concrete models to their solution. The instruction helped students in the experimental group to identify their mistakes, understand the usefulness of concrete models and lead to large improvements in performance for the experimental group. Keywords: concrete visualization. models; chemistry Dash-Wedge Diagram (Sometimes referred to, as perspective formula): In a Dash-Wedge diagram (Figure 1a), the molecule is oriented with the backbone carbons 1 at the two 4-way intersections of lines on the left and right of the diagram. Dashed lines represent bonds to atoms that are going into the page (below the plane of the paper). Wedge lines represent atoms that are coming out of the page (above the plane of the paper). Solid lines represent bonds to atoms that are in the plane of the paper. CH 3 education; H CH 3 H H 3 3 C C Introduction The literature in science education and chemistry education in particular, shows that interconnected cognitive skills, such as visualization, construction of mental models, model based reasoning, and representational competence are essential for acquiring mastery in the discipline (Kozma & Russell, 2005; Coll, 2006; Justi and Gilbert 2006; Treagust & Chittleborough, 2001). Kozma & Russell (2005) define ‘representational competence’ in the context of chemistry as ‘a set of skills and practices that allow a person to reflectively use a variety of representations or visualizations, singly and together, to think about, communicate, and act on chemical phenomena in terms of underlying, aperceptual physical entities and processes’. Representational competence is particularly important in organic chemistry. Organic chemists use several different representations of molecules, including different kinds of diagrams, models, and equations, for different purposes. For example, three kinds of diagrams are commonly used in organic chemistry and are introduced in the introductory college course on this topic. Mastering these diagrams is challenging, because they use different conventions to represent the three-dimensional (3-D) arrangement of atoms in the molecules in the two-dimensions of the printed page. They are also drawn from different orthogonal perspectives. This paper describes a study in which we examined students’ ability to translate between these models, and tested an educational intervention that was designed to improve their representational competence using 3-D molecular models. Examples of the three types of diagrams are given in Fig. 1 and their conventions and a brief description of each is given below. H H OH H CH H 3 H OH 3 C CH CH 3 H 3 C H CH 3 a. Dash-Wedge diagram b. Newman projection CH 3 HO H H H CH 3 c. Fischer projection d. Ball-stick model Figure 2: 2-Butanol molecule presented in three types of diagrams and concrete models used in Figure 1: 2-Butanol molecule presented in this three study types of diagrams and concrete models used in this study Newman Projections: In a Newman projection (Figure 1b), the molecule is oriented with one backbone carbon in front of the other. The front carbon is located at the intersection of the 3 lines (noon, 4 o’clock and 8 o’clock around the circle). The substituents (atoms or groups of atoms) at the ends of these three lines are attached to the front carbon. The rear carbon is behind the circle. The substituents at the ends of the shorter lines connected to the circle (2 o’clock, 6 o’clock, and 10 o’clock around the circle) are attached to the rear carbon. Carbon backbone: longest series of covalently bonded carbon atoms in an organic compound.