Studying Crystal Structures through the Use of Solid-State Model Kits Deborah Polvani Sunderland* Department of Chemistry, Washington & Jefferson College, Washington, Pennsylvania 15301, United States * S Supporting Information ABSTRACT: A solid-state crystal structure laboratory exercise for undergraduates in either a general chemistry course or a more advanced inorganic chemistry course is described. Students explore the lattice arrangement of atoms in unit cells by building models supplied by the Institute for Chemical Education. Emphasis is placed on building three-dimensional visual models of various crystal systems to display close packing of atoms, to identify tetrahedral and octahedral holes, to reveal number of atoms per unit cell, and to highlight ion coordination numbers and size differences. The relationship between solid-state bonding and a material’s physical properties is emphasized for elemental carbon. KEYWORDS: First-Year Undergraduate/General, Second-Year Undergraduate, Laboratory Instruction, Inorganic Chemistry, Hands-On Learning/Manipulatives, Crystals/Crystallography, Solid-State Chemistry, Solids M ost modern general chemistry textbooks will devote a chapter to instruction of solids and crystalline materials. It is interesting to note that, until recently, solid-state and materials chemistry has not had a prominent role in the undergraduate chemistry curriculum, and efforts to provide instructional materials to help modernize introductory courses have been addressed through the Ad Hoc Committee for Solid- Sate Instructional Materials formed in 1990 1 and in several of their publications. 2-4 Specifically, one way to help illustrate the connection between a crystalline solid’s atomic-level structure and its physical properties is through the use of crystal-lattice models. Considering the recent emphasis on solid-state materials at the undergraduate level, it perhaps is no surprise that there is only a limited collection of published laboratory experiments and classroom demonstrations directly related to construction and manipulation of crystalline models. A search of this Journal 5-10 resulted in a few examples from either home- built resources or commercially available kits. One online resource 11 was found that describes kits from the Institute for Chemical Education (ICE), which are the kits utilized in this laboratory experience, and another presented an activity utilizing virtual models of ionic structures. 12 Other references touted the general advantages of teaching chemistry through the use of physical models, 13,14 though there were no emphases on any particular model sets. Using a combination of physical and virtual models to supplement instruction in general and organic chemistry courses has distinct advantages. 15-17 These results show that students can benefit from using both physical and virtual models alongside each other. The physical (plastic) models provide something tangible for students; they can be touched and manipulated in three dimensions, and students tend to enjoy the tactile experience afforded when working with spheres and sticks. Virtual, or computer-based, models are available in several different types such as ball-and-stick, stereo line, or space filling. In addition, operations that include energy minimization or other mathematical functions and unlimited colors and sphere sizes are possible with the virtual models. Significant improvement in student understanding can be attributed to their exposure to physical and virtual models and the active learning that these methods provide. The laboratory exercise presented here utilizes physical crystal-lattice model kits from the Institute for Chemical Education (ICE) 18 that are currently sold with a detailed instruction manual. 19 The instruction manual is designed to give “layer by layer” directions for building three-dimensional crystal structures by dropping spheres through intentionally placed rods sticking up out of a template base (Figure 1). The instruction manual only provides directions for building the models; it does not prompt the students to answer questions about particular structures based on their observations. We, however, wish to extend the usefulness of this clever kit to the classroom by describing a set of activities in which students can participate as a lab experience. This experiment was designed as a three-hour laboratory session for our Introduction to Inorganic Chemistry course and has been included for the past four years. Students take this one-semester undergraduate course in their second year toward completion of a chemistry degree or to help fulfill their general chemistry requirements en route to a health professional Published: February 25, 2014 Laboratory Experiment pubs.acs.org/jchemeduc © 2014 American Chemical Society and Division of Chemical Education, Inc. 432 dx.doi.org/10.1021/ed400367x | J. Chem. Educ. 2014, 91, 432-436