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

The results of this study indicate that learning only emphasizes the verbal representation will result in the student having difficulty in understanding the chemical material, especially on the concept of atomic structure. The student difficulty lies in the interpretation of the phenomenon of sub-micro about models of atoms and distinguishes based on visual images created by students. The difficulties can also be caused due to the characteristics of the atomic model of an abstract nature of sub-microscopic scale, and in learning, students are not trained in conducting imagination representation of the phenomenon of sub-micro. These results are consistent with studies of Suits & Hypolite (2004) reported that students were not given learning with visual representation model of the atom, would have difficulty in understanding the phenomenon of the Bohr model of the atom when they learn, this is probably due to the abstract nature of the atomic model representation. Chemistry learning can be done through visualization or conceptual model expressed through the image of the structural model that describes the relationship between the concepts chosen by the students in creative problem-solving (Hilton & Nichols, 2011). Therefore, learning the concept of an atomic structure should be done through modeling. Modeling structures used in learning are able to lower cognitive positively, so that the effectiveness of learning within easy reach, the level of student understanding becomes higher, and eventually, students will experience satisfaction in learning (Hsu, 2014). In addition, it is also necessary a strong effort in learning to form a mental model of students, so that students' awareness in learning can be improved (Chudzicka-Czupała, Lupina-Wegener, Borter & Hapon, 2013).

The research findings show that most students have an understanding of chemistry on a macro scale with a simple structure, as a result of the lack of students' understanding of the relationship between the macro, sub-micro, and symbolic levels. If the students' understanding can be improved, then the mental model's students will be able to be cultivated and persist longer in their brains. The effects of scientific imaginative are not always direct, but tend to be durable (Hu et al., 2013) and mental models students will be easier to upgrade to a "target" (Sunyono & Yulianti, 2015). So, students use models to connect the observed phenomena and scientific explanations, and through this process, they form their own mental models (Park, 2006)

One implication of this research is the study of chemistry at the high school need to be established with a strategy that is able to optimize the ability of the creative imagination of students in an effort to improve the ability to reason, interpret and represent the molecular scale chemical phenomena. Learning by involving multiple representations is that students have the ability to reason, interpret, and represent a molecular level chemical phenomena, so that students can more easily solve chemical problems associated with abstract concepts, such as the concept of atomic structure. Referring to the statement some experts that the mental model is an internal representation that can be used by a person to think, to reason, interpret, predict, and provide an explanation of an object encountered (Cañas, Antoli & Quesada, 2001; Greca & Moreira, 2000) , it can be said that the mental models affect the cognitive development of students. Thus, the model student mental models can be built from the experience, training, and learning. Therefore, learning by involving visual representations related to chemical phenomena will be very helpful in fostering students' mental models (Sunyono, Yuanita & Ibrahim, 2015). Learning chemistry with a focus on image/visualization is part of the imaginative pedagogy that can expand and enrich the students' ability to reason.

Another indication of the results of this study is the implementation of learning chemistry in some schools in the province of Lampung - Indonesia is still not oriented to the optimization capabilities of the creative imagination of students. Learning that takes place has not been able to facilitate students in using the imagination's ability to develop the skills of thinking and reasoning power is high. The difference between the results of students from different schools because of differences in the application of learning strategies from teachers. In this case, the school is located far from the provincial capital (School C: students who are in the company's industrial/agro-industry) are likely to be able to excite the imagination of students, so that students' mental models that appear better than students who were in the neighborhood of employees and vendors or students in a farming environment. The results of interviews with students illustrate that schools located far from the provincial capital have implemented learning by using visualization to describe the structure of atoms and molecules. Visualization is done simply by using materials that exist around students such as fruits (oranges, guava, fruit distance, and others). This can be seen from students' answers to the mental model tests that provide a better visual representation of atomic structure than schools in the provincial capital (school A) and schools close to the provincial capital (school B). Thus, it can be said that the learning strategy applied in schools located far from the provincial capital is more appropriate in generating the students' creative imagination compared to schools located in the provincial capital and schools close to the provincial capitals.