Research Article Students knowledge on particulate nature of matter in Chemistry

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1 ONLINE ISSN : Volume 4, Issue 2, Research Article Students knowledge on particulate nature of matter in Chemistry Angelina I. Makaye 1, Patrick A. Ndunguru 1 and Stelyus L. Mkoma 2 * 1 Department of Education, Faculty of Science, Sokoine University of Agriculture, P.O. Box 3038, Chuo Kikuu, Morogoro, Tanzania 2 Department of Physical Sciences, Faculty of Science, Sokoine University of Agriculture, P.O. Box 3038, Chuo Kikuu, Morogoro, Tanzania ABSTRACT This study investigated students understanding of particulate nature of matter using a model for relating microscopic processes to macroscopic changes in chemistry. The study was carried out at Mbalizi secondary school in Mbeya municipality and involved 375 students selected randomly from form II, III and IV. The students were presented with test items which required them to use particle model to infer macroscopic chemical events they meant to depict. The results show that for students across the three classes, making the association between microscopic entities and macroscopic events was problematic and not entirely straightforward. The implication for chemistry education is that students are not always able to display consistent reasoning about particulate nature of matter unless they have appropriate representational model to base their thinking. The knowledge of their conceptual misunderstandings, however, provides a basis for a good teaching point and for changing pedagogical approaches in chemistry. Keywords: Science Education, Secondary Students, Microscopic and Macroscopic Model, Particulate Matter, Tanzania INTRODUCTION The task of teaching students chemistry concepts meaningfully is sometimes rather complicated and not fulfilled (Treagust et al., 2003). A student s difficulty in comprehending certain concepts is likely to be attributable to his or her failure to listen to and to understand what the teacher or textbook has to say. One factor that is related to students understanding difficulties in chemistry problem solving is an inadequate mental representation of the chemical reality being considered or thought of, in contrast to physical intuition. The major reason why students are unable to solve problems in chemistry is that in most cases the chemical concepts on which the problems are based do not make sense to them (Erduran, 2001). Generally it is accepted in chemistry that all substances are composed of small indivisible particles called atoms, molecules and ions. However, the concepts of atomic and molecular structure are very difficult for the students. Furthermore there is evidence which shows that most of chemistry textbooks contain a number of cognitive gaps that are likely to impact on students development of ideas. The textbooks rarely address limitations and history of the development of particle models (de Jong et al., 2005) and few secondary chemistry textbooks include exercises that require students to actively use particle models for relating observable phenomena to microscopic entities (Erduran, 2001). On the other hand, Treagust et al. (2003) suggested that there is a tension between teaching macroscopic chemistry and difficulties of explaining macroscopic changes in terms of the behaviour of microscopic particles. * Corresponding author stelyusm@gmail.com

2 MAKAYE et al. 649 Despite the efforts being done by different scientists and different authors to explain the particulate nature of matter (Maskill et al., 1997; Harrison and Treagust, 2000, 2002), most secondary students still have difficulties on understanding the concept. Studies in different countries show that students cannot distinguish some of the fundamental concepts on which knowledge of the particulate nature of matter is concerned (Harrison and Treagust, 2000). Similar studies in Tanzania are lacking and therefore, this study aims to find out students knowledge and understanding of the particulate nature of matter in chemistry using particulate model representation. METHODOLOGY A qualitative approach was employed for this study. The study was carried out at Mbalizi High school in Mbeya municipal (8 56'0"S, 33 22'0"E). The school was purposefully chosen due to its location where it was easy to reach the target population. The study sample, which comprised of 375 chemistry students, was drawn from form II, III and IV. These classes were selected because the topic under examination (particulate nature of matter) is supposed to have been covered (taught) according to the ordinary level chemistry syllabus. Hence gaining information from the three classes was thought would provide a useful basis for comparison. The 375 sampled chemistry students were provided with test questions describing the nature of qualitative thinking and reasoning about particulate nature of matter in chemistry. The test questions were multiple-choice type test items, where students were also required to give reasons for their responses. To answer the questions students were required to refer to the particulate model given in Figure 1. The students attempted the test at a close supervision so as to avoid the influence of ones results by the other. The content of the test was examined for reliability and clarification of difficulty terms was provided. It should be noted that sample size used in this study did not necessarily pose validity to the study problem of this nature. However, the study used a research made test questions; and through this the validity was already established. Collected data were tabulated and analyzed using simple descriptive statistics. Figure 1: Particulate Model Presentation of Substance, Mixture, Compound, and Physical and Chemical Change The symbols represent the following Symbol Represent the following Atoms of one kind Atoms of another kind Molecules formed when these atoms bind one another

3 MAKAYE et al. 650 RESULTS AND DISCUSSION Demographic Characteristics This study involved a total number of 375 students taking chemistry as a subject at Mbalizi secondary school. Of those 64%, 20% and 16% were in form II, III and IV, respectively of their study and 63.7% were males and 36.3% were females. The students were in the age group of 14 to 18 years old. The mean age of all students was 16 years old and majority aged of below 18 years old. Microscopic Particles The students were presented with the test questions and asked to select one option from the multiple choice-type questions and provide reasons for their choice. The results are summarized by number of responses for each of the options and the reasons for choice are presented in actual quotes for ease of reference. Table 1 shows results for test questions about the basic microscopic concepts for understanding particulate matter. Question 1 was about atoms and molecules and students understanding of the concepts pure and substance were examined. The rule that pure means one kind of particle seems to had been understood and applied. For example, pure was viewed as only atoms of the same kind. But the rule for a substance which should include everything around us, both elements and compounds, was understood or considered (96%). However, in the very few cases (4% of all students), depicting only atoms of the same kind. When the reasons of choice were analyzed, a pure substance was interpreted as pure substance has only one type of atom ; pure substances are elements not mixed with anything else, and pure substances are atoms of the same kind. About 4% of students in form II, III and IV gave similar responses mentioning as their reason for the incorrect choices (b to e) as, only one kind of atom is found, atoms are not bonding and each box show a set of atoms of a single kind ; not combined with other atoms. So from the results the 4% of the students interpreted pure substances as elements only and not as compounds as well, having more than one type of atom in a definite molecular arrangement. On the other hand, majority (96%) of students chose correct option (a) suggesting that they understood that both atoms and molecules are included in pure substances, explaining that it could be composed of molecules, compounds or atoms of a single kind. Question 2 also required two decision rules, that is, is it pure? and is it a compound? The reasons given for the correct choice (d), were mostly the same number of atoms of definite combination/composition, molecules of the same kind, or pure compounds are made up of the same molecules as arranged in definite ratio, which indicate understanding. About 25% of the students selected the incorrect options (a) and (b) which means that they were unable to distinguish between elements and compounds or between mixtures and pure substances respectively as represented. Also the term pure substance seems to have confused students as the reasons given by respondents for choice (b) indicate that they only regard substances as pure when the same kind of atoms are grouped together in the figure or box, or any combination in the figure is of the same kind of atoms. However the question comes behind as, how do they understand the term compound? About 26.8%, 14.3% and 5.1% of the FII, FIII and FIV students respectively selected option (a) with reason that the atoms, that is the circles are sticking together to form compounds ; compounds are mixtures formed after the combination of two molecules apparently without taking into account the qualifying term pure. Option (a) includes a mixture (Fig. 4) and a pure compound (Fig. 5), with each figure having the same number of each type of atom. The equal number of atoms (Fig. 4) seems to be the basis for the choice of option (a). The given reasons were the numbers of circle shaded and

4 MAKAYE et al. 651 unshaded are equal, there is equal number of atoms to form a compound and all atoms have equal ratios so they represent pure compounds. Here, a considerable number of students (32%, option c) did not realise that changes in the arrangement of atoms and molecules in definite composition as represented by the circles (unshaded, shaded and touching) had something to do with whether or not it was a pure compound (macroscopic property) or of the same substance is of some concern. TABLE 1: Results for Test Question About the Basic Microscopic Concepts for Understanding Atoms and Molecules Test Questions Form II (n= 239) Form III (n=77) Form IV (n=59) Total Students (n=375) Question 1. Which figures stand for pure substances? A (Figs. 2, 3, 5 & 7) B (Figs. 2, 4 & 7) C (Fig. 4 & 7) D (Figs. 3, 6 & 7) Question 2. Which figures stand for pure compounds? A (4 & 5) B (Figs. 2 & 7) C (Figs. 1 & 4) D (3 & 5) E (6 & 7) Question 3. Which figures stand for a mixture of compounds? A (Figs. 1 & 3) B (Figs. 1 & 4) C (Fig. 4 only) D (Figs. 1, 4 & 6) E (Figs. 1 & 6) Question 4. Which figures stand for a mixture of elements? A (Figs. 1 & 6) B (Fig. 1 only) C (Fig. 6 only) D (Fig. 4 only) E (Figs. 1 & 6) Question 5. Which figures stand for a mixture? A (Figs. 1, 5 & 6) B (Figs. 1, 4 & 6) C (Fig. 6 only) D (Figs. 3 & 5) E (Fig. 4 only) Macroscopic Particles Test questions 3, 4 and 5 required students to use the particle model to identify observable macroscopic functions involving mixtures of compounds, mixtures of elements and mixtures, respectively. Nearly 57% students in Form II, 62% in Form III and 70% in Form IV chose the correct option (b) for test question 3. The successful subjects understood both what a compound is and a mixture as a combination of two or more substances in which the substances whether as elements or compounds retain their distinct identities. As a result they reasoned that a mixture of compounds is formed by different kinds of compounds mixed together... formed by the atoms (shaded and unshaded circles). This indicates that students could correctly define a compound or a mixture. For example, reasons for choice included: it is a mixture of compounds, and because the figure has a mixture of every compound in it.

5 MAKAYE et al. 652 About 24% of students in the three classes who chose option 3(c) selected only one out of the two correct figures that depicted a mixture of compounds. Whether the difficulty here is as a result of excess demand on information processing capacity (working memory) that is, the maximum amount of items of information an individual can attend to at any one point in time (Onwu, 1996) or one of closure is still not clear. Students who chose option 3(a) appear to have difficulty with the concept of mixture, because that option included figure 3, which depicts a pure compound and not a mixture. The conceptual misunderstanding is apparent from their reasoning. They reasoned that option 3(a) represented a mixture of compounds because all atoms involved are combined with one another, and that atoms in figures 1 and 3 undergo the same kind of bonding-circles are touching. This means that they are all compounds. Those who chose the incorrect options had difficulty in distinguishing between elements and compounds. For example, option 3(d), was selected by about 5% of students. The reasons for the choice were mainly that it is a mixture of different elements and compounds and there are different kinds of compounds and elements in the Figures. These suggest that students understood the characteristic features of the particulate model that they were looking at. Yet they chose to include a mixture of elements in their choice. However it is suspected that the difficulty in this option 3(d) also involves understanding the difference between a mixture of elements, and a compound composed of those elements. For question 4 about 54% student in form II, 72% in form III and 59% in form IV (4c) had no difficulty relating the particulate model to a definition of element. It is a mixture of elements because they are uncombined atoms of different kinds. For the 8% of students who chose option 4(a), could mean that the symbolism of theoretical particles (circles) touching at the sub-microscopic level holds no meaningful relationship to what exist at the visible level. Perhaps, this can involve no more than making the abstract symbolism clear, ensuring that students understand the full significance of the symbols. About 27% of all the respondents had the correct answer for test question 5(d) that asked the relationship of a mixture of substances, which includes both a mixture of compounds and a mixture of elements, to the provided particle model. The difficulty may be resulted from excess informational load on processing capacity or working memory as suggested by Case (1980) or due to lack of appropriate mental structure for the chemical situation was not clear. The other option with the highest respondents was option (b) (31%), which indicates a mixture of compounds only. For about 8% of form II, 5% of form III, and 5% of form IV students chose options (b) for test question 5; making the distinction between mixtures and mixtures of compounds and then relating those distinctions to the sub-microscopic representations were problematic. Therefore the particle model seems to be new and counter intuitive for the beginning secondary student. Table 2 shows students response to particle behaviour about physical and chemical changes. It present test questions 6 and 7 which are more conceptually demanding. Question 6. Which of the following would represent what takes place in a physical change? a) Starting with particles represented in Figure 6 and ending with particles represented in Figures 2 and 7 b) Starting with particles represented in Figure 1 and ending with particles represented in Figure 6 c) Starting with particles represented in Figures 2 and 4 and ending with particles represented in Figure 3

6 MAKAYE et al. 653 d) Starting with particles represented in Figures 2 and 7 and ending with particles represented in Figure 4 e) None of the above would represent a physical change. Question 7. Which of the following would represent what takes place in a chemical change? a) Starting with particles represented in Figures 2, 6 and 7 and ending with particles represented in Figures 1, 3, 4 and 5 b) Starting with particles represented in Figures 2 and 7 and ending with particles represented in Figures 1, 3, 4 and 5 c) Starting with particles represented in Figure 6 and ending with particles represented in Figures 2 and 7 d) Starting with particles represented in Figure 2, 6 and 7 and ending with particles represented in Figures 1, 4 and 5 e) None of the above would represent a chemical change. The comparatively poor results for the respective question 6 and 7 (involving about 60% success rate for physical change and less than 41% for chemical change processes (Table 2) need to be further explained. Making the association between the macroscopic event as defined and the sub-microscopic model as represented in the Figures requires a great deal of intuition. In answering question 7, most of the students appeared not to have considered stoichiometric factors. Yet they seemed to know that chemical changes involved the rearrangement of atoms or molecules. For example, 23% of the students selected option 7(c) and gave as reason because when you start with different elements you end up with a compound... a chemical change involves a rearrangement of elements to a new substance, a compound can be separated by chemical change like combustion to form its constituent elements. Interestingly enough, some of the students explanations were quite consistent. Thus of the students who gave chemically incorrect explanation for their choice of options in test questions 6 and 7, did so by the application of what appeared to be logically sound thinking based perhaps on their everyday usage and experience of the term physical change as evidenced in these statements: a physical change is when we use a magnet to separate a mixture and it is because you can form carbon dioxide from carbon and oxygen; the combustion of carbon is a chemical change. Question 7, it should be known that the introduction of stoichiometric considerations for the choice 7(e) did pose a problem since the test question did not stipulate the subjects needed to take stoichiometry into account. Noticing that comparatively (41%) of students chose e as their option and it would seem that the majority did not take stoichiometry into account or simply ignored it. It is interesting that about 26% students of form II, 18% of form III and 14% of form IV selected option (b) with reasons that starting with atoms of two kinds (Figs 2 and 7) and ending with particles of several different molecules (Figs. 1, 3, 4, and 5) represents a chemical change without the stoichiometry because when you start with different elements you end up with a compound... a chemical change involves a rearrangement of atoms of different elements to a new substance.... Therefore, from this fact it is possible that the subjects might not have been limited by the number of atoms of each kind shown in the figures. Also even if stoichiometry had been the required assumption, Figs. 2 and 7 leading to Fig. 5 should have been an acceptable chemical change and ought to have been included as an option. Offering it might have served to draw the students attention to the possibility of considering stoichiometry. So from the written answers of those students who gave incorrect explanations we can glean that their understanding of chemical change or physical change is still based on some category of experience where those terms have come to be associated with specific events, like a

7 MAKAYE et al. 654 physical change is when we use a magnet to separate a mixture, in the context of the students day-to-day classroom activities (Onwu, 1996). It is therefore feasible, that even the term chemical change or physical change may be understood in a figurative, experiential or contextual sense. Chemical or physical change is not as some attribute of the particulate nature of matter, or as a principle with some generality; rather it is just a term to be accepted as part of the idealised world of science. It has been explained that a contextual understanding of the utility of chemistry is likely to be of use in this study especially in motivating students to seek full explanation of macroscopic phenomena; to go beyond the visible, in a way that is likely to encourage them to seek particle and symbolic representations for chemical phenomena (Harrison and Treagust, 2000; Krnel et al., 2003). Generally, this explanation for poor performance is somewhat speculative. The point remains, however, that from a teaching point of view, multiple conceptual changes about representational particle interactions would have to be in place if we are to bridge the gap between the intuitive and the scientific framework, Any conceptual change has to be ontological because as evidenced in the study done Harrison and other scientists, students tend to use macroscopic properties to infer what the corresponding particles are like, and how they interact, whereas the expert, uses a theory of particle behaviour to explain observable macroscopic characteristics (Harrison and Treagust, 2002). Clearly these are different ways of looking at the relationship between submicroscopic particles and macroscopic properties and therefore demand different approaches for the novice to assure understanding. It is equally revealing that, the conceptual problems encountered by the three classes were similar, involving many consistent and intuitive misunderstandings. From a constructivist point of view, the much needed conceptual change will most likely be evolutionary rather than revolutionary, requiring new instructional strategies that are informed by preliminary findings such as those of this study. TABLE 2: Students Response to Particle Behaviour About Macroscopic Events Test Questions Form II (n= 239) Form III (n=77) Form IV (n=59) Total Students (n=375) Question 6. Which figures denote what takes place in a physical change? A B C D E Question 7. Which figures denote what takes place in a chemical change? A B C D E CONCLUSION The aim of this study was to investigate students understanding of the particulate nature of matter. Students difficulties in relating microscopic entities and macroscopic phenomena in chemistry were investigated. It is evident that many students found it difficult to imagine macroscopic events microscopically using the particle model. There was, however, remarkable consistency in the ways students from the three participating classes reasoned about the different test items. It was equally obvious that certain misconceptions persisted over the years. Exactly how we can make atoms and molecules real to students is not very

8 MAKAYE et al. 655 clear. We cannot show atoms, and besides the models that we employ are often poor approximations that are often used to portray certain properties which sometimes end up distorting other properties. Secondly, a student s better understanding of the concepts underlying the particulate nature of matter may also be inhibited, precisely because of the teacher s haste to cover mechanical skills and get on with the teaching of chemistry. As a result, effective particle concepts, which ideally are developed over time, are introduced too quickly. This practice is likely to produce little understanding. Nonetheless, students explanations in all their inconsistencies and diversity do provide excellent material to the teacher as potential conceptual resources, to be discussed, investigated and used as activities to provoke active thinking on the students part. Multiple conceptual changes may be needed to help students develop a scientific understanding of particle theory. Hopefully, the kind of research reported here would catalyze action along lines of mix of conceptual addition and revision. ACKNOWLEDGMENT Authors gratefully acknowledge the cooperation of head of school and chemistry teachers, and to students who willingly took part in this study. We also acknowledge special research funds granted to the first author from the Higher Education Students' Loans Board (HESLB) of Tanzania. REFERENCES de Jong O., Van Driel, J.H. and Verloop, N. (2005). Pre - service teachers pedagogical content knowledge of using particle models in teaching chemistry. Journal of Research in Science Teaching, 42, Eduran, S. (2001). Philosophy of chemistry: an emerging field with implications for chemistry education. Science and Education, 10, Harrison, A.G. and Treagust, D.F. (2000). Learning about atoms, molecules, and chemical bonds: A case study of multiple-model use in grade 11 chemistry. Science and Education, 84, Harrison, A.G. and Treagust, D.F. (2002). The particulate nature of matter: Challenges in understanding the microscopic world. In J. K. Gilbert et al. (Eds.), Chemical Education: Towards Research-Based Practice. Dordrecht: Kluwer Academic, pp Krnel, D., Glazar, S.S. and Watson, R. (2003). The development of the concept of "matter": A cross-age study of how children classify materials. Science Education, 87(5), Maskill, R., Cachapuz, A.F.C. and Kouladis, V. (1997). Young pupils ideas about the microscopic nature of matter in three different European countries. International Journal of Science Education, 19, Onwu, G.O. (1996). Understanding pupils difficulties in associating macroscopic events with pictorial representations of microscopic entities in school chemistry. Research in Curriculum Studies, 1, Treagust, D.F., Chittleborough, G. and Mamiala, T.L. (2003). The role of submicroscopic and symbolic representations in chemical explanations. International Journal of Science Education, 25(11),