29 Jun 2015

Lewis Structure Challenge

In-Class Activity

Submitted by David A. Laviska, Rider University

This in-class activity is designed to give general chemistry students practice with drawing Lewis structures. Small groups of 3-5 students compete for points by creating hypothetical molecules that meet criteria (numbers of elements and atoms) assigned by the professor. Beginning with simple molecules, the basic challenge format calls for increasingly complex criteria in successive rounds of competition. One optional variation also allows student groups to challenge each other for bonus points.

Learning Goals: 

Students will practice skills relating to

  • accurately representing bonding in simple molecules using the convention of Lewis Dot Structures.
  • recognizing the periodicity of valence electron configurations in Groups within the Periodic Table.
  • creating hypothetical molecules based on an understanding of valence shell electron configurations.
  • counting electrons in order to rationalize bonding patterns.
  • assigning formal oxidation numbers to covalently bonded atoms.
  • assigning formal charges on individual atoms.
  • identifying the presence of resonance structures and drawing them accurately.
Implementation Notes: 

The competition involves students working collaboratively within their groups to draw Lewis structures for hypothetical molecules. In successive rounds of competition, the instructor assigns criteria for the compounds to be drawn as outlined in the Faculty Guide (to be downloaded from this webpage). The students choose non-metal elements from the Periodic Table and attempt to construct valid Lewis structures that satisfy the criteria within a limited timeframe. Points per round are awarded for correct structures, with bonuses based on identifying ideal geometry and formal oxidation states as outlined in the Faculty Guide document. Each round should be timed (to be determined by the instructor, but generally kept short, e.g., 2-4 minutes, in order to add a time-pressure facet to the competition). After time has been called in each round, structures should be shared with the instructor for discussion and immediate awarding of points. Additional strategies and notes are discussed in the Faculty Guide document.

Time Required: 
At least one class period
Evaluation Methods: 

Ideally, a quiz should be given during the next lecture period (or another convenient time) following the in-class exercise. Given the format of the in-class activity, the quiz could include both traditional structures (e.g., SO42-) as well as criteria similar to those dispensed during the Lewis structure challenge activity. Additionally, mid-term and/or final examinations should include questions that revisit the skills involved in drawing accurate Lewis structures.

Evaluation Results: 

This is a new Learning Object that has been developed over the last several months and it has not yet been tested in the classroom.

Creative Commons License: 
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