Introduction. ConcepTests are a method of in-class instruction developed
by Eric Mazur for introductory physics courses. Mazur has published information
on the method and recently established a World Wide Web site of physics
questions (1). The intent of this article is to give chemistry teachers
some ideas for implementing the method based on its use in classes at the
University of Wisconsin-Madison, expanding on a brief description that has
been published (2). Principal virtues of ConcepTests are their ease of use
and versatility, and a number of examples are included herein.
The basic idea behind ConcepTests is peer instruction: Students who
have just grasped a concept may be able to explain it to a classmate more
effectively than the instructor for at least three possible reasons: 1.
The insight is fresher. If the instructor learned many of the fundamental
chemistry concepts some time ago, it is easy to forget whatever obstacles
there were to mastering the ideas initially; in cases for which the concept
was obvious, it can be difficult to have an appreciation for why it may
not be obvious to someone else. 2. Classmates speak a more common
jargon that facilitates communication. Years of sanding explanations can
leave a teacher disconnected with regard to how to cast an appropriate explanation
for his or her students. 3. The teacher is the authority figure who
hands out the grades. This represents a barrier for some students in terms
of establishing a suitable level of comfort at which they could learn directly
from the instructor.
Besides engaging students in helping to communicate the course concepts,
the method gives the teacher feedback in real time on the appropriateness
of the pace of the course. As will be described below, it is easy to tell
when most of the class has or has not mastered a concept, and lecture explanations
and speed can be adjusted on-line to reach the majority of the class.
From a teacher's perspective, ConcepTests are a wonderful pedagogical
tool because they can be used with virtually any kind of content and
require very little time investment and little or no resources: A teacher
simply identifies a number of key ideas that form the basis for the lecture
and "packages" as many as desired as ConcepTests. As Mazur has
shown, it is possible to collect a considerable amount of enlightening statistical
information from student responses, particularly with modern touchpad technology,
but a show of hands is sufficient to obtain good qualitative insights into
the level of student understanding.
From a student's perspective, ConcepTests provide a clear indication
of the key concepts that a teacher values and some immediate feedback
as to whether he or she understands an idea or is going to need to invest
additional effort in mastering it. Students have expressed appreciation
for the fact that the time provided in lecture to conduct the ConcepTest
provides an opportunity to digest information and to look at ideas from
several points of view.
To establish a culture of cooperation and make the use of ConcepTests a
natural part of the course, it has proved advantageous to grade the course
on an absolute scale rather than on a curve. That is, students are told
at the outset that a certain number of total points in the class guarantees
a particular letter grade (2, 3). Students are willing to help one another,
since they recognize it will not jeopardize their grade.
Implementation. There can be particular concern with the initial
use of ConcepTests if it is the first time "the class is turned over
to the class." ConcepTests discussed here have been used in large-lecture
introductory general chemistry classes of nonmajors (although a few students
subsequently became majors) of typically 200 to 350 students, and in recitation
sections of about two dozen. Introducing ConcepTests on the first day of
class works well, although there is no reason why its introduction could
not occur at any time during the course. A typical introduction has been
to pick an engaging topic, pose a question, and provide two to four choices
to stimulate discussion. Of course, it is important to ensure beforehand
that students are seated near enough to one another to be able to converse.
As an example, a topic covered in the first lecture of general chemistry
concerns our ability to image atoms using a scanning tunneling microscope
(STM). A simple demonstration piques curiosity: two wires are brought together
and when they are close enough to touch, an electrical circuit is completed
and a bulb is lighted (4). This raises the question of how close the wires
need to be for electrons to flow as electricity. After explaining that a
wire tip can be prepared that terminates in a single atom and that it can
be scanned over the surface of the other wire in atomic-scale increments,
the picture shown below is sketched on the blackboard (or an overhead transparency
can be prepared). The class is told that they will be asked in a moment
for a show of hands as a response to possible answers to the following question:
"Which curve describes how the electrical current will vary as the
tip-to-surface distance changes, A or B?" After giving the class a
few moments for reflection, the show of hands is requested: "How many
of you think curve A is the appropriate relationship? How many of you think
it is curve B?" Usually some hands are observed for each answer. There
are also students who don't commit to either answer. At this point the fun
begins: "I'd like you to turn to your neighbor, introduce yourself,
and then convince him or her that your answer is correct." There may
be a moment of stunned silence, as though the class is thinking, "You
mean, we can talk in class?" Then, typically, loud discussion ensues.
The intensity level of class discussion that follows often determines
how much time to allot for it. After a suitable period of time has passed,
typically marked by a lull in the discussion level, the instructor interrupts
and asks for another vote. If by show of hands most students have converged
on the correct answer, the instructor can briefly affirm why it is correct
and move on. If the class has converged on the wrong answer or not many
hands are raised, this is a signal that the class is not following, and
the teacher has some choices. One choice is to provide an additional clue,
if the question lends itself to that, and repeat the process, with or without
a discussion period; or, the instructor can try to explain why another answer
is more appropriate. The value of the ConcepTest, as noted above, is that
the pace of the course is adjusted on-line as class mastery is assessed
in real time.
Some variations on the delivery of the ConcepTest are noteworthy.
In some instances, a large majority of the class immediately chooses the
correct answer (this is often the case with simple counting-type questions,
such as whether Na+ has 10, 11, or 12 electrons), in which case the discussion
period can be skipped and a quick explanation provided as to why 10 is the
correct answer. With more challenging questions like whether the absorption
of light by a solution is linear or logarithmic (this is coupled to a demonstration;
see sample questions below), there is an opportunity to walk around the
lecture room and listen to some of the discussion, which can provide the
instructor with some insight into possible misconceptions. Some concepts
lend themselves to a series of related choices and the initial show of hands
can be eliminated: For example, after reviewing a rule-of-thumb for predicting
when to expect extended structures and when to expect discrete molecules
based on chemical formula (5), students are asked to indicate the appropriate
structure for each participant in the reaction, after giving them a little
time to discuss this with their neighbor. The instructor then requests shows
of hands, asking in turn whether Na, Cl2, and NaCl is a discrete molecule
or extended solid.
An example that has been used in the first lecture for the second semester
course of our two-semester introductory sequence, by way of review, is to
ask students to indicate whether a relatively simple equation is balanced
("How many think it is? How many think it isn't?")
How many ConcepTests are desirable? During a 50-minute lecture period, typically
three to six have been used, depending upon how many are tied to demonstrations
(see examples below). Some colleagues use a single ConcepTest. The class
quickly becomes accustomed to this approach. It has been found to boost
attendance considerably in the large lecture presentation, for which attendance
has not been mandatory.
Instructor Attitude. When giving a ConcepTest, it is helpful to be
prepared for anything in the way of class response. Hearing students animatedly
discussing chemical concepts in the lecture hall can be an exhilarating
experience, and it is gratifying when the class converges on the correct
answer. Some occasional acknowledgment of their success may be well received
by the class. On the other hand, convergence on a wrong answer or obvious
confusion is best served by a patient explanation or an attempt to use an
alternative approach to communicate the concept.
An experience worth relating occurred with a demonstration involving a concentration
gradient, which was used as a vehicle for introducing concentration cells
and related electrochemical concepts. A pair of aqueous cupric ion solutions,
one concentrated and dark blue and the other dilute and light blue, were
separated by a removable plastic barrier, as sketched below. The prediction
asked of the general chemistry class in a ConcepTest was what would happen
when the barrier was removed: Would the two solutions, now in direct contact,
retain their colors; would the dark solution become even darker and the
light one even lighter; or would the two become indistinguishable in color?
The initial vote was in favor of the dark solution becoming darker and the
light one lighter! The instructor may occasionally be thunderstruck by predictions
such as this and can use them to advantage to obtain the class' attention.
In this case, the barrier was simply removed and the color of the entire
solution shown to became uniform. This demonstration engaged the class in
discussions of diffusion and its directionality and of the spontaneous direction
of current flow in an electrochemical concentration cell.
A similar result occurred during a demonstration involving the reaction
of Ni and Al powder, pressed into the shape of a bar, to make, quantitatively,
NiAl alloy in a thermite-like reaction (6; and see below). Magnetic properties
of the bar before and after the reaction were shown to be completely different.
The ConcepTest question was whether an elemental analysis conducted before
and after the reaction would yield the same or different results. About
half the class initially thought the analyses would be different! The ConcepTest
drove home the true significance of an elemental analysis through peer instruction.
About the Collection. The examples of ConcepTests given here have
been used in a two-semester general chemistry sequence. Preceding each are
key words indicating the topic(s) associated with the question. Instructors
will recognize many of the questions as relating to standard material. Our
experience has been that framing ideas with ConcepTests has engaged the
class in making predictions and constructing interpretations. This often
puts a very different spin on the way these concepts and demonstrations
are perceived by the class. In some cases material is taken from "Teaching
General Chemistry: A Materials Science Companion," and is so indicated
by "Companion." Answers are bold-faced. A short index of the key
words has been included to facilitate finding questions for a given topic.
The authors would welcome comments and additional suggestions for questions
applicable to courses throughout the chemistry curriculum (concept@chem.wisc.edu).
References
(1) Mazur, Eric Peer Instruction: A User's Manual; Prentice Hall: Upper
Saddle River, NJ, 199, pg 253. Also, World Wide Web server (URL:http://mazur-www.harvard.edu).
(2) Ellis, A. B. Chemtech; 1995, 25, 15-21.
(3) Herschbach, D. R. J. Chem. Educ. 1993, 70, 391.
(4) Ellis, A. B.; Geselbracht, M. J.; Johnson, B. J.; Lisensky, G. C.; Robinson,
W. R. Teaching General Chemistry: A Materials Science Companion; American
Chemical Society: Washington, DC, 1993, pgs. 15-16.
(5) Ibid. pgs. 49-50.
(6) Ibid. pg. 332.
Acknowledgments. We thank Sheila Tobias and Eric Mazur for making
us aware of the ConcepTest methodology. We thank Larry Dahl, Clark Landis,
John Moore, Fleming Crim and David Phillips for helpful comments. The construction
of the Chemistry ConcepTests web site has been generously supported by the
National Science Foundation through grants awarded to the ChemLinks (NSF
DUE-9455918) and New Traditions (NSF DUE-9455928) curriculum reform projects.
