Research in chemical education has shown that while students (K-20) can perform well on tasks that require use of algorithmic and symbolic skills, they struggle with tasks that require conceptual understanding of chemistry. One area where such a trend has been observed is the Particulate Nature of Matter (PNM). A number of factors have been attributed to this struggle in developing conceptual understanding, for example, the abstract nature of the subject and concepts, the fact that most teaching and assessments focus on algorithmic understanding of content, and a missing connections to students' everyday lives. This semester-long grounded theory study examined college level general chemistry students' conceptual understanding of the particulate nature of matter across three different types of reactions. Students were asked to balance the chemical equations, and then draw particulate representations of the reactions. A sample of 10 participants was interviewed to probe for their understanding of underlying chemistry concepts represented by the equations and their particulate drawings. The study sought to compare students' understanding at the symbolic and particulate levels, look at trends across the different reactions, how the trends changed over the semester, and to reveal struggles with fundamental chemistry concepts. Analysis of the results shows that there is a gap between students' understanding at the particulate and symbolic levels, inconsistency in students' understanding across the three chemical reactions over the course of the semester, and struggles with fundamental chemistry concepts. This study reinforces the need to teach and assess for conceptual understanding, not just in chemistry, but in other subject areas as well. Suggestions for teaching and research are also made. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]