Student Reasoning Strategies Concerning Periodic Trend

The periodic table is recognized as one of the most powerful tools in science. While it is included in virtually all high school and undergraduate general chemistry curricula, it remains a mystery to many chemistry students who find it impossible to decode. Students are often able to predict periodic trends concerning atomic radius, ionization energy, and electronegativity, however they experience significant difficulty when trying to explain why these trends occur. One way to explore the cause of these difficulties is to focus on the reasoning strategies used by students as they attempt to explain periodic trends.;This study investigated student reasoning strategies used to explain periodic trends in atomic and ionic radius, ionization energy, electronegativity, and reactivity. A theoretical framework of scientific reasoning, as it applied to qualitative problem solving, was utilized to identify how the problem solving constraints of domain specific knowledge (DSK) and heuristics were utilized by students as they attempted to explain the periodic trends. This phenomenographic study used semi-structured interviews to assess student reasoning strategies, as well as selected exam and assignment questions to determine the DSK for each student.;The findings suggested that student understanding in the domain of electrostatic forces had the greatest influence on the type of reasoning strategies used. Those students with adequate understanding of electrostatic forces had more resources with which to construct explanations that integrated several scientifically appropriate force related factors. Those students without adequate understanding concerning electrostatic forces tended to limit themselves to the use of one factor that was not always adequately justified. They also tended to exhibit fixation by focusing on the same factor for multiple situations, even when that factor was no longer the most appropriate. When presented with an unfamiliar problem there was an increase in the number of one-factor strategies used, with a corresponding decrease in the number of force related explanations. This study suggested that an analysis of student explanations about difficult chemical topics might be helpful in diagnosing the underlying causes of student learning difficulties, and it also highlighted the need to help students learn how to formulate appropriate scientific explanations.