Effects of using particulate model as a teaching strategy on the learning of writing chemical formulae and balancing chemical equations

This study investigates the effects of an innovative teaching strategy, namely Particle Teaching Strategy, which incorporates both the microscopic and symbolic levels of chemistry during instruction, on the students’ chemical knowledge, conceptual understanding and problem solving performance. The topic for the study is writing chemical formulae and balancing chemical equations. A total of 74 secondary three students from two intact classes in a government boys’ school were involved in this study. One of the two classes was taught using the Particle Teaching Strategy (treatment group), while the other class was taught using the traditional teaching method (control group). Three test instruments, namely Chemical Knowledge Test, Conceptual Understanding Test and Problem Solving Test, were designed and administered as pre-tests to the students before teaching the topic and as post-tests after the students were taught the topic. The results of the study and its implications for teaching chemistry will be discussed. Theoretical Framework In the past few years, research studies had found that students had difficulties in visualising particles’ behaviour and arrangement in a chemical reaction microscopically as well as in relating chemical equation as a symbolic representation of chemical reaction at the microscopic level. When Yarroch (1985) examined 14 high school chemistry students who had been successful in balancing chemical equations, he found that more than 50% of these students were unable to draw correct diagrammatic representation of the symbolic chemical equations at the molecular level. In another study by Ahtee and Varjola (1998), they found that the first year senior secondary students and first year general chemistry undergraduate could write a chemical equation using the chemical symbols, but these students failed to describe what was actually going on in the reaction at a microscopic level. Similarly, the study by Wolfer and Lederman (2000), which looked into students’ ability to connect between conceptual and computational understandings in stiochiometry, had found that most of the students were unable to depict the microscopic representation of a chemical reaction between chlorine molecules and an excess of aluminium atoms, given the symbolic chemical equation. From their interview with these students, Wolfer and Lederman found that they could not understand how the “two chlorine atoms in each chlorine molecule were split to give three chloride ions in each aluminium chloride produced”. Nurrenberg and Pickering (1987) conducted a study to investigate on whether students who were successful in solving problems would have acquired an understanding of the chemical concepts involved in the problems. They found that most of these students who were successful 489 problem solvers lacked conceptual understanding of symbolic chemical equations at the microscopic level. Therefore, it is evident from the review of the above research studies that students often treat chemical equations as mathematical puzzles in which the number of the same atoms on both sides of the chemical equations have to be equal, rather than thinking of the equation as a representation of a dynamic and interactive chemical process. Georgiadou and Tsaparlis (2000) evaluated the effectiveness of two teaching methods in enhancing Greek lower secondary school students’ learning of the abstract and complex concepts of chemistry. One of the teaching methods was based on the developmental psychological theories proposed by the psychologist Robbie Case (Case, 1978), while the other was based on the macroscopic, microscopic and symbolic levels of chemistry as proposed by Alex H. Johnstone (Johnstone, 2000). In the teaching method based on Case’s proposal, it showed how the students could improve their learning of chemistry through guided discovery experiments, construction of solid models by students and concept maps. In the other teaching method based on Johnstone’s proposal, known as “three-cycle”, the students were taught in the first cycle at the macroscopic level, this was followed by going through the same material again in the second cycle at the symbolic level and finally in the third cycle, the same material was covered at the microscopic level. The results showed that the teaching method which involved the three levels of chemistry was most effective in enhancing students’ learning of chemistry. The process of going through the same material three times at the different levels (macroscopic, microscopic and symbolic) could help students to make the mental links between the three levels of chemistry, thus strengthening their conceptual understanding As suggested by Ben-Zvi, Eylon and Silberstein (1987), an appropriate interpretation of the chemical information underlying an equation requires learners to understand many aspects of chemistry such as (i) the interactive nature of the chemical reaction represented by the equation, (ii) the quantitative relationships among the reactant and product particles (meanings of coefficients and subscripts), and (iii) the structure of the reactants and products. This explains why many students find it difficult to understand the chemistry concepts underlying the chemical equations. However, the conceptual understanding of chemical equations can be improved, if the relationship between the mechanics of balancing equations and the underlying concepts at the microscopic level are constantly emphasized in the teachers’ instruction (Yarroch, 1985). As such, this study intended to investigate the effect of a teaching strategy known as Particle Teaching Strategy (PTS), which enabled students to visualise particles’ behaviour and arrangement in a chemical reaction microscopically as well as in relating chemical equation as a symbolic representation of chemical reaction at the microscopic level, on students' acquisition of chemical knowledge, conceptual understanding and problem solving performance. Three research questions for this study are as follows: Q1. Is there a significant difference in the chemical knowledge of the topic on writing chemical formulae and balancing chemical equations among the students who are taught using Particle Teaching Strategy and those who are taught using Traditional Teaching Strategy? Q2. Is there a significant difference in the conceptual understanding of the concepts of the topic on writing chemical formulae and balancing chemical equations among the students who are taught using Particle Teaching Strategy and those who are taught using Traditional Teaching Strategy? Q3. Is there a significant difference in the problem solving performance among the students who are taught using Particle Teaching Strategy and those who are taught using Traditional