Particle model students’ understanding

In chemistry, perhaps because of the significance in visualizing molecular strac-ture, there has been a focus on how students perceive three-dimensional objects from a two-dimensional representation and how students mentally manipulate rotated, reflected and inverted objects (Stieff, 2007 Tuckey Selvaratnam, 1993). Although these visualization skills are very important in chemistry, it is evident that they are not the only ones needed in school chemistry (Mathewson, 1999). For example, conceptual understanding of nature of different types of chemical bonding, atomic theory in terms of the Democritus particle model and the Bohr model, and... 

Students Understanding Probed Through Presented Diagrams The Particle Model of Matter... 

Novick and Nussbaum (1978) explored students understanding of the particle model of matter... 

To be able to explain chemical reactions, students will have to develop mental models of the submicroscopic particles of the substances that undergo rearrangement to produce the observed changes. However, students have difficulty in understanding submicroscopic and symbolic representations as these representations are abstract and carmot be directly experienced (Ben-Zvi, Eylon, Silber-stein, 1986, 1988 Griffiths Preston, 1992). As a result, how well students understand chemistry depends on how proficient they are in making sense of the invisible and the untouchable (Kozma Russell, 1997 p. 949). 

A teacher may ask his or her students about their understanding of the particle model of matter. If the teacher needs a written questionnaire, he or she could use a diagnosis test created by Kathrin Brockmann [22] at University of Muenster. She developed the test Particles of Matter , utilizing some of the very well-known misconceptions held by most students. Finally, she evaluated this test with about 160 German students aging from 13-15 in the 7th grade [22]. 

Result. The main result of the empirical research was as follows knowledge concerning complex reactions seems very poor, very few memorized formulas remain from university lectures, but no mental models concerning complex particles. The students saw the bracket symbols like [Cu(Fl20)4]2+ in then-lectures, but they got no real idea about the existence of these complexes as particles in solid blue copper sulfate crystals or in the solution of this salt. Students saw the complex formulas of the process of dissolving solid aluminum hydroxide by the well-known complex reaction - but could not understand these formulas. 

In the first group of papers, students difficulties have been reported as mainly related to mathematical problems arising from differentials in the rate equations and to the inter-relation of kinetics with thermodynamics. This means that they are centred on specific points that are taught only at this level and are related to more complex models than the colliding particle . There is a clear distinction between the methodology used in such papers and those used in studies of pre-university students understandings. Higher... 

The Particulate Nature of Matter is vital to understanding chemistry. Chemists explain phemonena in terms of particle behavior. Several chemical education research studies have helped expand the theory of how students learn about particle behavior. Early studies established the lack of student understanding of particle action, while later studies examined treatments or interventions to help students think in terms of particles. These later studies led to a number of implications for the chemistry classroom and our understanding of how students build mental models to visualize particle behavior in chemical and physical phemonena. 

Johnson (75) described four distinct types of particulate mental models that move along the novice-expert continuum. Students using the first type of mental model have no idea of particles. They see matter as continuous. In the second type, students draw particles, but see the particles as something separate from the substance. For example, they draw molecules inside the sugar cube or draw water molecules, but will say that water is in between the drawn molecules. In the third type of mental model, students believe that the particles make up the substance, but attribute the macroscopic properties of the substance (the element or compound) to the individual particles. For example, they draw water molecules in steam as wavy or sodium atoms as silver. In the fourth type, students understand that the particles make up the substance AND that the macroscopic properties are attributed to the collection of particles, not to individual particles. As instructors, we want to move our students towards more complete expert mental models. 

Dissolving provides a context to strengthen and develop students understanding of the basic particle model, but also to recognise its limitations. 

Students poor understanding of the particle model does not help as many do not recognise that the wax and the flame are particulate. Very few students understand that the flame includes particles of hydrocarbon. This is obviously going to be true of younger students who have not yet met the ideas of hydrocarbons, but is also prevalent among older students who have. 

We expect that students will develop a model competence by participating in such a learning environment. In our case model competence means that students have an adequate understanding about the nature of particle models and that they can use particle models to explain macroscopic phenomena in various situations. This is to say that if we could observe in students argumentations an appropriate microscopic thinking and adequate thinking in models, as well as a renunciation of macroscopic thinking in the micro-world, then we could say that students have a model competence. 

In parts of the pre-test, it beeame evident that students had already learned eoneepts about the particle structure of matter (Figure 7). As a result, students aheady had a relatively adequate knowledge concerning the forces and distances between particles, or of the movement of particles. In comparison to these microscopic attributes, conceptions of the macroscopic attributes and of the behaviour of the particle model were not suitable nor did a model of understanding exist. 

In their initial stndies, Pallant and Tinker (2004) found that after learning with the molecular dynamic models, 8th and 11th grade students were able to relate the difference in the state of matter to the motion and the arrangement of particles. They also used atomic or molecular interactions to describe or explain what they observed at the macroscopic level. Additionally, students interview responses included fewer misconceptions, and they were able to transfer their understanding of phases of matter to new contexts. Therefore, Pallant and Tinker (2004) concluded that MW and its guided exploration activities could help students develop robust mental models of the states of matter and reason about atomic and molecular interactions at the submicro level. 

Dalton s Atomic Theory was an important milestone in the development of chemistry, but modern chemistry students will correctly note that it was incomplete, and in some cases, just plain wrong. For example, not all atoms of a given element are identical, because Dalton did not know about the existence of isotopes. Likewise, we now know that atoms are comprised of still smaller particles and that nuclear processes convert atoms of one element into atoms of other elements. By the very nature of science, when a hypothesis, law or model—no matter how dearly held—fails to make correct predictions, it must be discarded or modified. So, significant portions of Dalton s original theory have been modified. However, the importance of Dalton s theory can hardly be understated and should not be assessed by whether or not it was correct in the finest details, but in how it provided a working foundation that guided current and future scientists in their quest to understand the physical world. 

Pure Acids and Acidic Solutions. In this exercise, the students are supposed to state the similarities and differences between pure sulfuric acid and the 0.1 molar solution, and to schematically draw the smallest particles in two model beakers (see Fig. 7.4). Correct answers regarding the hydronium ions and sulfate ions in dilute solutions can be found in only 10% of the answers or model drawings. Approximately 45% of the answers approach it from the dilution effect either the drawings depict for example, symbols for sulfuric acid molecules with larger distances in the solution or hard to understand spherical models (see Fig. 7.4). 

Summary. It is pointed out that, in order to avoid misconceptions, the introduction of ions is very important ions have been dealt with as basic particles of matter according to Dalton s atomic model (see Chap. 5). In order to understand the charges of ions and the change of ions and atoms by electron transfer, the differentiated atomic model with nucleus and electron shells should be introduced. With the assistance of a clear terminology, it is easy to formulate half-reaction for the oxidation and reduction steps, the number of electrons to be transferred can be clearly recognized. Finally, if mental models -for instance, from involved atoms or ions in Galvanic cells or in batteries - are relayed and drawn by the students themselves, then they could more easily see through the redox processes or even perhaps be able to repeat them independently. In all explanations, one should pay attention that the observations should be done at the substance level, but that the interpretations and discussions of reaction equations should consequently take place at the level of the smallest particles as atoms, ions and molecules. 

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