First Year Odyssey

Chalk Talk

Establishing the Right Chemistry by Charles Kutal

From Chalk Talk: Teaching Tips from the UGA Teaching Academy, edited by Loch K. Johnson.

Teaching General Chemistry to undergraduates presents challenges that confront many instructors whose students “must” take an introductory science course as a prerequisite to more advanced courses in their major. The concepts, principles, and examples covered, although essential for a basic understanding of the subject, often seem dull and unrelated to a student’s everyday experiences. Moreover, the sheer volume of material that needs to be covered for students preparing for the GRE, MCAT, or other professional examinations can be daunting.

There is no single recipe for successful teaching, but over the years I have developed a short list of teaching tips that work for me. None are revolutionary, but they have been effective in the course that I have taught for the past eight years—second semester General Chemistry for Honors students (CHEM 1312H) and chemistry majors (CHEM 1412). As background, this three credit hour course typically enrolls 85-95 students, almost all of whom are BS majors with a relatively good science/mathematics background. I present the material in an interactive lecture (non-PowerPoint) format that aims to engage students. There is a required one-credit-hour laboratory course that meets for three hours each week and is essential to the overall learning experience.

The Tips:

  • 1. Prepare for each and every lecture. Pay special attention to the first one-to-two minutes, whichsets the tone for that lecture.
  • 2. Less is better. Each lecture stresses two, or at most, three key points. Students are expected to fill in the gaps by reading the textbook and working assigned problems.
  • 3. Key concepts are clarified by a tight linkage of lecture material to laboratory work. Each experiment is discussed in lecture the day prior to the laboratory.
  • 4. Always make time for questions. Students are told that they are expected to stop me with questions. When they see that each question is treated as being worthwhile, the two-way exchange becomes habit-forming.
  • 5. Occasional video clips and demonstrations are helpful. They can illustrate key points in a time- effective manner and the change of pace helps to invigorate flagging attention spans.
  • 6. Periodically assess students understanding of key concepts. One easy method is the one-minute quiz. I pose a relatively easy question that addresses some important point that has been discussed and ask the students to write a brief answer on a sheet of paper, which they then submit, unsigned. After class I read the responses and identify any misconceptions or confusions. Several student responses—from way off to really good—are displayed and discussed at the beginning of the next lecture.
  • 7. Challenge students with an in-class problem. Another method for assessing student understanding is to pose a more complicated problem (usually one that entails a degree of analysis and critical thinking) and ask the students to discuss it in small groups for three-to-five minutes. Then some of the groups orally report their solutions and, more importantly, explain their thought process.
  • 8. Be available. I stay after lecture to answer any lingering questions, have posted office hours (which few students attend), and very frequently check messages on Web CT (which students use a lot). Optional review sessions are held before each exam.

These tips provide a global view of how I teach the course. But what about those “magic moments” when the light bulb suddenly turns on and students grasp a particularly difficult concept? For me, this magic is most likely to occur by linking the concept to something tangible, usually an experiment, or demonstration in which students are active participants. In the laboratory, students gain an understanding of the properties of a non-Newtonian fluid by sticking a finger into a mush of corn starch and water. Withdrawing the finger is easier when done slowly rather than rapidly, and relating this behavior to a person struggling in quicksand provides real-life context. Tearing apart a disposable diaper and testing the properties of the super absorbent polymer filler provides another example of introducing chemical concepts in context.

But my best example of turning on the light bulb for students involved explaining the directional motion of an electron in an atomic orbital located on a metal atom surrounded by six groups (termed “ligands” and designed by L in the accompanying diagram). Rather than using the professionally drawn figure appearing the textbook to explain this conceptually difficult topic, I draw the diagram on the left (only really big) in chalk on the floor of the lecture hall and invite the students to leave their seats and gather around the drawing. I choose four students, two of each gender, designate each as a ligand, and place them at the appropriate locations in the diagram. I then explain that ligands possess electron density, which is negative charge, and Coulomb’s Law teaches that a negatively charged electron moving in an orbital (represented by the four lobes in the diagram) pointing at a ligand will be repelled and thus experience and unfavorable rise in energy. I emphasize the point by acting as an electron and moving toward one of the students, and as I approach, say, “do not take this personally, but you repel me.” This comment always elicits a laugh but serves to emphasize a key point. To finish the story, I mention that the electron prefers to move in an orbital that points between the ligands (lying along the dotted lines in the diagram) and thereby minimizes the repulsion it experiences. Students freely ask questions and make comments in a relaxed and interactive environment.

This simple demonstration has proven to be a very effective teaching tool. When, on the next exam, students are asked to discuss the physical principles that underlie the ligand field splitting of atomic orbitals, most can provide an accurate explanation using proper scientific terminology. Comments received from some students on the end-of-course evaluation form or during chance encounters in the Chemistry Building convince me that this demonstration resulted in a “magic moment” for them.