In the Classroom
The Molecular Model Game Stephanie A. Myers Department of Chemistry and Physics, Augusta State University, Augusta, GA 30904;
[email protected] As evidenced by past issues of this Journal, games are a popular method of reviewing material (1–3), with many games, such as Crute’s “Synthetic Relays” (4), using teams. In the game described in this paper, Lewis structures and molecular geometries are practiced in such a way that students must operate as a team to solve a problem. This game gives students an opportunity to review Lewis structures and VSEPR theory after it has been covered in class. The game would probably work well in a high school setting, but may be adapted to other levels by changing the difficulty of the problem. In this game, students work in teams of three, each with a different job. Although each student may give advice, no team member may do another’s job. Therefore, the entire team is needed to complete the task. The score of each team can be translated into an assignment grade or extra credit points that are independent of who wins. Materials Each team needs a modeling kit, a pencil, and a stack of problem sheets kept on the instructor’s desk. The instructor must arrange the room so that the “runner” of each team has a clear path to the instructor and so teams can work together conveniently. For a simple and inexpensive modeling kit, modeling clay and toothpicks may be used, conveniently stored in a snacksized, sealable plastic bag. Unless a problem with more than three different atoms in a single molecule is assigned, three colors of clay are sufficient. Students can divide the clay into as many pieces are necessary to create atoms for their molecule. The problem sheets consist of a single problem on its own sheet of paper (or half-sheet), so that students only work on one problem at a time. Stacks for each group contain the same problems but on different colored paper. Using different colors decreases the likelihood of a mix-up between the problem sets of each group. It also helps sort the correct answers by team for scoring. In each stack, the same problems can be piled in a different order so that teams are working on a different problem at any given time. The exception is the first problem on the stack that simply requires students to record the name of each person on the team. Using this as the first problem is usually sufficient to prevent two teams from winding up with the same color (or problem stack), and records the composition of the teams for the instructor. The real problems consist of a name or chemical formula of a covalent molecule or polyatomic ion. Students are expected to first draw the Lewis structure and then to build a model of the molecule or ion. (Molecules used in the problems are chosen at a level of difficulty appropriate for the class.) For example, a typical set of problems, which include shapes from linear to octahedral, may be: xenon tetrafluoride, carbon dioxide, sulfate ion, SF6, H2S,
CH3COOH, NO3−, IF4−, PCl3, and CH2O. Normally 10– 12 problems are sufficient for a 50-minute class period. Teams The game is played by teams of three. The teams can be self-selected, randomly chosen, or thoughtfully assigned, as appropriate for each class. Among themselves, the students assign each member of the team a job. These jobs are “runner”, the only person allowed to consult with the instructor; “writer”, the only person allowed to use the pencil; and “builder”, the only person allowed to manipulate the modeling kit. While jobs within a team may be rotated during play, this is often logistically difficult to implement. If the class size is not a multiple of three, a team of two works better than a team of four. With two students, one can do two jobs. With four team members, one student does not have a job and is therefore not fully participating. Normally if a student must do two jobs, one of the jobs is runner. The Play Once the teams are settled, and the instructor says Go!, the runner goes to the instructor’s desk, collects the first paper on their stack (the one where the names of the team will be listed) and the modeling kit, and then returns to the group. The remaining problems for each group must always come from the same stack of paper, which is also the same color as the one containing the group’s names. Within the group, the writer puts everyone’s name on paper and the runner returns it to the instructor in return for the first structural problem. The entire group discusses the problem, with the writer drawing the Lewis structure and the builder making a model of the molecule. The runner then takes the Lewis structure and model to the instructor. If both the model and Lewis structure are correct, the runner takes the next problem to the group. If either is incorrect, the runner has the choice to try the problem again or to try a different problem. If a different problem is chosen, the incorrect one is moved to the bottom of the pile to be attempted again after all the other problems have been completed. When the runner chooses to attempt the same problem again, the instructor may choose to impart a little advice to the runner (which can then be relayed to the group). Examples of advice might include: “recount your valence electrons”, “the Lewis structure is incorrect”, and “how would those lone pairs affect the shape?” For consistency it is best to decide what kind of hints will be given before the game starts. Likewise, the amount of detail required in the student answers should also be considered. For example, must the students show lone pairs on their model? Are lone pairs on the model required or optional? Play continues until time runs out or each group completes all its problems. If one group completes all the
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In the Classroom
problems, the remaining groups may continue working until the period ends, allowing all students an equal opportunity to earn points. The first group to complete all the problems is declared the winner. If no group completes all the problems, the group that completes the most problems wins. Scoring The number of points earned is based on the number of problems correctly completed by the group. A minimum number of correct problems might be set to count as a completed assignment. This number is usually set low enough that most groups can accomplish it. Any problems completed beyond the minimum number could constitute extra credit. The extra credit problems do not necessarily have as high a point value as those used in scoring the assignment. The first group to complete all the problems does not gain further points but is awarded a nifty prize, like periodic tables or thermochromic pens. Such prizes are usually leftovers from National Chemistry Week activities. Second and third prizes
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might also be awarded. If appropriate, time may be left at the end of the game for an awards ceremony. Variations While this game is usually used as an in-class activity, it might also make an interesting change from a standard molecular models lab. The same format might also be used to review other topics that require the use of a tool. For example, the builder could instead become the “calculator” who is the only person allowed to use a calculator. The calculator variation might be used for a set of stoichiometry or equilibrium problems. Literature Cited 1. Haworth, D. T. J. Chem. Educ. 2001, 78, 466–477. 2. Waddell, T. G., Rybolt, T. R. J. Chem. Educ. 2000, 77, 471– 485. 3. Russell, J. V. J. Chem. Educ. 1999, 76, 481–503. 4. Crute, T. D. J. Chem. Educ. 1992, 69, 559.
Journal of Chemical Education • Vol. 80 No. 4 April 2003 • JChemEd.chem.wisc.edu
