Mental models of atomic structure concepts of 11th grade chemistry students

The mental model can be described as a conceptual model, mental representation, mental imagery, mental processes, a construction which cannot be observed, and personal cognitive representation (Chittleborough & Treagust, 2007; Johnstone, 1993). According to Buckley & Boulter (2000) that mental model is an intrinsic representation of an object, idea or process that generated individually for cognitive function. A person uses the mental model to express the reason, describe, explain, and predict phenomena in a model of expression in a variety of formats (eg, verbal descriptions, diagrams, simulations or models of concrete) to communicate their ideas to others or for troubleshooting.

A group of researchers in the field of education and learning of chemistry using the definition of mental models as "a representation of an idea, object, event, process or system" (Gilbert, 1997). A mental model is an internal representation, a cognitive representation that is used to understand the phenomenon, and to describe, explain, predict, and, sometimes, control them (Johnson-Laird, 1980; Johstone, 1993; Treagust, Chittleborough & Mamiala, 2003). By using this definition, a group of researchers in chemistry study has shown that learning with a variety of representations is essential to increase students' understanding of chemistry concepts, especially the use of visualization representations to explain the phenomenon of sub-micro (Devetak, Erna, Mojca & Glažar, 2009; Yakmaci-Guzel & Adadan, 2013), so that students' mental models can be recognized. Mental models are global and dynamic constructs, integrating various elements, which "may be understood as fully implemented representations of objects, states, or events" (Rickheit & Sichelschmidt, 1999) and serve as mental simulations that accomplish cognitive tasks such as understanding, reasoning, prediction, and creative problem solving (Johnson-Laird, 1980). For this reason, Franco et al. (1999) argued that studies of students' mental models may offer a better understanding of students' alternative conceptions. Students' mental models that are reported in the literature are inconsistent with the actual scientific or teaching models, and are not only considered flawed or found to contain some misconceptions (Coll & Treagust, 2003; Vosniadou & Brewer, 1992) but are also usually simplistic (Coll, 2008; Coll & Treagust, 2003). Therefore, the research reported in this paper seeks to add to the body of literature, by providing in-depth insight into students' understanding of atomic structure as expressed through their mental models.

Some research on mental models has indicated that indicated that many students have a very simple mental model of chemical phenomena, such as models of atomic and molecular are described as the discrete and concrete structure but do not have the skills to build a mental model (Johnstone, 1993; Buckley & Boulter, 2000; Park, 2006; Wang, 2007). In addition, students construct mental models it is possible to do through the transformation of learning that emphasizes the three levels of chemical phenomena (Coll, 2008; Yakmaci-Guzel & Adadan, 2013; Sunyono, Yuanita & Ibrahim, 2015). Park (2006) reported that a creative visualization of the history of the development of atomic theory by using visual representations to the level sub-micro to explain how the atomic structure was formed based on theories that developed. Theories of the development of the atomic model drawn visually ranging from particle model (assuming of Democritus and definition of Dalton), the core model initiated by the findings of Thomson and Rutherford, Bohr model and the model of quantum mechanics. The picture can evoke sensory involvement of students, enriching experience and further by drawing, then the sensory participation in the body can provide a better learning experience (Hsu, 2014). The pictures are examples of creative imagination that can help students in understanding the phenomenon of sub-micro because the image can facilitate the process of thinking, and this image will also be able to help students in growing and improving their understanding of the diverse curricular topics. Through the visualization of images of sub-microscopic phenomena, students will more easily in the reasoning of the physical object is encountered, so that their mental model can be built easily. Thus, in assessing mental models, researchers used models expressed by the respondents surveyed, so that an interpretation of the research findings of researchers whose understanding is based on the mental models of the respondents expressed (Coll & Treagust, 2003). Some researchers have used a description of the question to determine a student's mental model. An example of a descriptive question asked to explore the student menta model is "What is vapor pressure? Please explain your answer (Tumay, 2014). Through the students' answers to these questions, the researchers classify mental model into several categories, wait for the level of representation (physical or conceptual-symbolic, for examples, the idea about a chemical single bond as a pair of shared electron versus a pair of overlapped t orbitals from two atoms) and mobility (static or dynamic) models (Coll & Treagust, 2003; Wang, 2007).

The research questions
In this study, the nature of students' mental models of various levels of education is examined to identify and consider their conception of atomic structure. This paper is expected later has the potential to provide a better understanding of the difficulties students in in learning of atomic structure concepts. Hence, this study was conducted to answer the questions:

How are the characteristics of grade 11 students' mental models in understanding the concept of the structure of atoms?
What are the difficulties experienced by students in doing creative imagination to interpret chemical phenomena in growing mental model?