Chemistry Eduction in New Zealand February 2009
A Better Way to Teach With Analogies
Richard K. Coll
School of Science & Engineering, University of Waikato, Hamilton (email: [email protected])
A while back I attended a public lecture given by
Professor Alan MacDiarmid. Without ‘dumbing
down’ his talk or being in any way condescending, he was at pains to make his leading edge science understandable to an audience who probably
had little science knowledge. He naturally and
instinctively explained his science concepts using
analogies, peppering his talk with anecdotes and
comparisons between aspects of his science and
everyday life. I believe that he did this for a very
pragmatic reason - he felt his audience would be
able to better understand his science concepts if
they were related to something familiar.1 This is
the essence of the use of analogy, both in conversation, and in science teaching. In this article I spell
out how we can make better use of analogies in
science teaching. Uncritical use of analogy can, in
fact, interfere with science learning, and we need
to be aware of the pitfalls of inappropriate analogy
use, and know how we can avoid them. I’ll start
by telling you about the nature of analogies and
what education research tells us about why they
work and the circumstances in which they work
best. I’ll then talk about where analogies break
down as a pedagogical tool, and finish by working through the teaching of an abstract chemistry
concept using an analogy in some detail.
scale model of a shopping mall allows the viewer
to see what it might look like overall without focussing on the minutiae (e.g., which specific shops
will be part of the mall), a ball-and-stick model allows us to focus on the arrangement of atoms in a
molecule, and so on. Because of this, a model or
analogy is intrinsically limited compared with the
target. This is not a flaw of models, but an inherent feature of them and the modelling process; if
it were otherwise the model and target would be
one and the same! So, as is illustrated below in
Fig. 1, an analogy will be like the target in some
ways (the  and * symbols), and unlike it in other
ways (the  and # symbols):
■
*
*

■
■
■
model (Rm)
analogy (A)
■
*
analog (R1)
#
■
target (R2)
Fig. 1: An analogy is a type of model [above]
How Analogies Work
I have already alluded to the main way in which
analogies work, that is, by linking the unfamiliar
(i.e., what we are trying to teach or understand)
to something familiar.2 If we consider this further,
Analogies and Models
we see that we actually do this by linking or mapAn analogy is a type of model, and, like other ping attributes or features of the analog to the atmodels, its main aim is to simplify aspects of what tributes of the target (see Fig. 2 below).
we want to understand (typically called the target)
so as to allow us to focus on a particular part or Let me illustrate this process of mapping with
specific feature of the target. Thus, for example, a an example which I am sure is very familiar to
Analog
Analogy
Target
Analog attributes 1
Mapping of idea 1
Target attribute 1
Analog attributes 2
Mapping of idea 2
Target attribute 2
Analog attributes 3
Mapping of idea 3
Target attribute 3
Familiar idea or object
Scientific idea or object
Mapping
Fig. 2: Mapping of analogies and targets [above]
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Chemistry Education in New Zealand February 2009
you: the solar system model for the structure of
the atom. This model forms the basis of the BohrRutherford model of atomic structure. We say the
structure of the atom is like the planetary solar
system model in that the nucleus is like the sun
and the electrons orbit the nucleus in much the
same way as the planets orbit the sun. So here we
have mapped the analog attribute of the sun to the
target attribute of the nucleus, and the analog attribute of the planetary orbit to the target attribute
of the electron orbit.3 There are a couple of things
I want to comment on further here. Firstly, this
use of analogy illustrates a purpose or feature of
analogy use, that is, in the processes of knowledge
generation by scientists.4 Harrison & Coll (2008)
point out that for some scientific concepts (e.g.,
refraction) the analogy is the scientific concept!
Secondly, many people use analogies in the way
I have just done, i.e., fairly superficially. In other
words I have only mapped across a few attributes
(what we call a simple analogy). We tend to do this
because consciously or subconsciously we stop
because we feel we have made our point (e.g., in
the case above the way electrons orbit around the
nucleus). Technically every time we say, “This is
like that”, we are using analogy. However, it seems
the use of analogy is greatly enhanced if we map
more attributes across the two domains, or if we
explain the way or ways in which the analog and
target are similar. If we then explain the mapping,
we have what is termed an enriched analogy. So
if we say activation energy is like a car going over
a hill, because you have to add energy to get the
reaction to go, we have enriched the basic mapping that occurs in simple analogy, and shown the
way in which it occurs. To go further, if we use
multiple mappings together with explanations, we
have what is called an extended analogy. Let me
give you an example of an extended analogy. It
is hard for students to understand that most of a
hydrogen atom is, in fact, empty space, and the
relative distance of the valence electron(s) from
the nucleus to the perimeter of the atom is 5 x
10-11m. We can explain this using an analogy with
a sport stadium into which we place a grain of
rice. We would say the hydrogen atom nucleus
is like a grain of rice because both are relatively
small (the rice compared with the stadium and the
nucleus with the overall size of the atom); that the
region where the electron might be found is like
the playing area and the outermost seats in the stadium (because the electron is most likely found a
long way from the nucleus in the same way that
the outermost seats are a long way from the rice
grain); and the ratio of the nucleus to the electron
cloud is similar to the ratio of the size of the rice
grain to the size of the stadium overall.
To summarize, analogy works best when it is well
known to the student, when we map across as
many attributes as we can, and when we explain
explicitly the ways in which the analog and target
are similar.
When Teaching with Analogies
Breaks Down
This explanation of the use of analogy might
make it all seem pretty simple. You might think
all you need to do now is extend your analogies
a bit more than you have in the past, and everything will be fine. Well, there is a catch! Education research suggests that students do not think
in the same way as scientists or science teachers
– no great surprise there I am sure! But specifically with respect to the use of analogies, it seems
the main way things go wrong is that students are
either unfamiliar with the analog, or that they map
across attributes that are not valid; in other words,
they assume the analog and target are much more
similar than they actually are. A particularly common example of this is the so-called water pipe
analogy used to explain electric current. It seems
some students think electricity can ‘leak’ from
wires in the same way water can leak from a
pipe.
So how can we address this issue? There are three
features to the effective use of analogy in science
teaching. Firstly, as noted above, critical to effective use of analogy in science teaching is using an
analog that is familiar to your students. Secondly,
we need to map the ways in which the analog and
target are similar as much as we can. If we fail to
do this, students may do their own mapping and
assume some attributes are shared between the
analog and target when they are not. Thirdly, we
also need to map the ways in which the analog
and target are not similar. In other words, we need
to map unshared attributes, as well as shared attributes.
Models for Teaching with Analogies
The advantages and disadvantages of analogy use
in science classrooms spawned a huge research
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Chemistry Eduction in New Zealand February 2009
effort over a number of years, and as a consequence a number of models for science teaching
with analogies have been devised. I will describe
two of these, but will focus on one which I think
represents the state of the art.
Focus
Concept
As the first example Glynn (2007) identifies five
basic steps in teaching with analogies (TWA),
which address the points I mentioned above:
Analog
• Introduce the target concept
• Remind students of what they know of the analog
• Identify relevant features of the target
• Connect or map the similar features
• Indicate where the analogy breaks down, and
• Draw conclusions about the target.
Recent research suggests that because many
teachers have not been trained in the use of analogies, models like Glynn’s are helpful in providing
teachers with a fairly simple way of avoiding the
key pitfalls in analogy use in the classroom. However more recently, a different model - the FAR
guide - was developed with teachers (see Harrison & Coll, 2008). A distinguishing feature of
the FAR guide is the close involvement of teachers in its development and implementation. FAR
stands for Focus Action and Reflection, and, as
we shall see, these form the key components of
good teaching, including that which draws upon
analogies. I will briefly outline the FAR guide and
then move on to show you how to use it with a
specific example.
Table 1: Basic features of the FAR guide
Students
Action
Likes
Dislikes
Is it difficult, unfamiliar or
abstract?
What do the students already
know about the concept?
Is the analog something the students are already familiar with?
Discuss the ways in which the
analog and target are similar
Discuss the ways in which the
analog and target are unalike
Reflection
Conclusions
Was the analogy clear and useful,
or confusing?
Did it achieve the intended outcomes?
Improvements In light of the outcomes, are
there any changes that should be
made the next time the analogy
is used?
really quite simple, but has remarkable explanatory power. However, research suggests that it is the
fine detail of kinetic theory that students struggle
with; things such as the role of energy and collision theory. An important aspect of kinetic theory
is the way it is used to explain reaction kinetics,
via molecular collisions. Scientists talk about effective collisions as being necessary before reactions can occur. However, to students a collision
is a collision, and it is not obvious to them how
you can have effective and ineffective collisions.
The basic features of the FAR guide are detailed Let’s now use the FAR guide to explain effective
in Table 1.
collisions and their influence in reaction rates.
The developers of the FAR guide argue that it
works well, mostly because the steps in it are intuitive and easily understood, and that they are very
similar to what goes on with any good teaching.
Let’s now look at how we can use the FAR guide
with a specific example.
According to the scientific model, the rate of a
chemical reaction is dependent on the number
of effective collisions. One consequence of this
is that the higher the concentration (and some
other variables too, like temperature) the more
likely we are to see effective collisions, and thus
the reaction rate increases. The notion of effective
The Coconut Shy Analogy for
molecular collisions seems a reasonably intuitive
Effective Molecular Collisions
concept, yet reaction rate chemistry is, like other
The target concept of this example is one which aspects of kinetic theory, seldom well understood
is well reported in the literature as a topic that stu- by students. Most students are familiar with fairground competitions like the ‘coconut shy’ where
dents find difficult – kinetic theory.
you have to try and knock an object (e.g., a coKinetic theory is in my view a brilliant theory; it is conut) off a stand. Clearly, as with any analogy,
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Chemistry Education in New Zealand February 2009
you need to tailor the analog to something you are
sure your students are familiar with (think of appropriate activities from your local festivals and
agricultural fairs). Alternatively, this is a model
you could actually act out, making it an exciting,
and fun activity, but you will need a fair bit of
room to allow for inaccurate shots! The difficulty
students face when trying to knock a coconut off
the shy shows how infrequent effective collisions
are.
Let’s start the use of the FAR guide with the first
phase, the Focus phase which consists of three
parts; the concept, the students and the analog.
Table 2: Mapping the attributes
Analog — coconut shy
Ball and coconut
Number of attempts
Hitting coconut with ball
Likelihood of hitting
coconut
Speed of throw of ball
Close to the coconut
Target — effective
collisions
Reacting particles
Number of collisions
Effective collision
Likelihood of effective
collisions
Kinetic energy of reacting
particle
Concentration increase
log and target are unalike, that is, where the analThe concept here is that chemical substances are ogy breaks down:
made up of tiny charged or uncharged particles, • A hard, ball will be travelling much, much
and that chemical reactions proceed when bonds
more slowly than colliding particles
are broken and new bonds formed. Kinetic theory
models reactions as ‘effective collisions’, and ef- • There are many, many more particles present
in even a tiny amount of reacting substances
fective collisions result in bonds breaking. The rethan there are coconuts/balls
sultant particles can form new molecules by forming new bonds. In order to break a bond we need • In the coconut shy, one object is still (the cocosufficient energy to bring about an effective collinut) and the other moving (the ball), in kinetic
sion. The likelihood of effective collisions can be
theory both reactants are moving rapidly, and
increased by increasing the number of particles in
• Reactants are often confined to a reacting vesa given space (i.e., increasing concentration) and
sel, in principle you could throw a ball at the
by increasing the temperature (which increases
coconut from almost anywhere.
the velocity, and thus the energy of the particles).
Finally, let’s move on to the Reflection phase.
Education research suggests that students have
Again there are two parts, the conclusion and imdifficulty visualizing tiny, sub-microscopic parprovement of the analogy. A conclusion might foticles like atoms, ions and molecules. It is hard
cus on whether or not the students were able to hit
for them to visualize collisions and effective colthe coconut (if they acted out the analogy). You
lisions. They are more familiar with fun activities
will need to have plenty of balls on hand as the
like the ‘coconut shy’ seen in many fairs and fesstudents may get frustrated if they keep missing
tivals.
the coconut. Also the ball will need to be heavy
We can visualize an effective collision as an anal- enough to actually dislodge the coconut from
ogy, in which the analog is knocking a coconut the stand. If you act out this activity, a possible
off the stand at a fair (a competitive activity). The improvement might be that, you can have many
greater the number of attempts we are able to students all firing their ball at a single coconut.
make, the more likely we are to knock the coconut This is much more likely to result in an effective
off the stand and thus the greater the likelihood of collision. If they cannot hit the coconut, another
an effective collision! We can also throw the ball improvement might be to have the students stand
at the coconut harder, in which case it goes faster closer. This could then be related to the size of the
and if it hits it is then more likely to actually knock container (which could be indicative of concentration, as particles per unit volume).
the coconut off the stand (i.e., more energy).
Let’s now move on to the Action phase. First, we Teaching Chemistry with Analogies:
must map the attributes, that is, the way the ana- Some Additional Thoughts
log and target are alike (see Table 2).
Analogies can provide wonderful learning opporSecond, we must map the ways in which the ana- tunities for students. I want to finish off by giving
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Chemistry Eduction in New Zealand February 2009
you some more food for thought: other ways you The final comment I wish to make is that there are
can use analogies creatively.
some concepts for which you are best to use more
than one analogy. Multiple analogies can reduce
The key thing that makes analogies work as learn- the likelihood of a single analogy breaking down.
ing tools is the fact that they are familiar to the I will give you a couple of examples for the subject
students. So anything that relates to students’ lives of chemical equilibrium – a problematic topic for
will be immediately familiar (e.g., dating, sport, many students. We can compare activation energy
etc.). In our research we have often encountered with a hill as noted above, forward and reverse
situations where a teacher was trying to teach a reactions with walking up the down escalator, and
topic (with or without analogies) and a student air flight paths with reaction mechanisms.
said something like, “Hey sir is it like …’. In other
words the student introduced his or her own anal- Concluding Thoughts
ogy. One thing you can be sure of when this happens is that the analog is familiar to the student. Teaching with analogies can be arduous. It takes
So I suggest you latch on to any student-generated time to think up good analogies and as you can
analogies that arise in the classroom. Likewise, see from above, considerable thought to make
if you spontaneously think up an analogy when sure they are used well. A colleague and I recentyou react to looks of puzzlement (we call this a ly produced a book that contains over 50 analoteacher-generated analogy), take the analogy and gies (see Harrison & Coll, 2008). The analogies
develop it in the same way I did – using the FAR are explained in detail and then presented using
the FAR guide. Our own research has shown that
guide.
when used well, analogies are a powerful motivaI mentioned above that students appreciate activi- tional and conceptual tool: the FAR guide helps
ties like the coconut shy (i.e., they prefer to expe- avoid the pitfalls.
rience the activity rather than being told about it).
Another way to use analogies is to use role play. References
So, for example, if you are trying to model intra- Glynn, S. (2007). The teaching with analogies model. Reand intermolecular bonding you can get student to
trieved 07 August 2008 from http://www.coe.uga.edu/
link arms (intramolecular bonding) and get groups
twa/PDF/Glynn_2007_article.pdf
of students to then hold hands (intermolecular Harrison, A.G., & Coll, R.K. (Eds.). (2008). Using analobonding). Likewise humour used judiciously can
gies in middle and secondary science classrooms. Thousand Oaks, CA: Corwin.
add to the fun of learning with analogies. One example that immediately springs to mind is Licata’s Licata, K.P. (1988). Chemistry is like a … The Science
Teacher, 55(8), 41-43.
(1988) model for covalent bonding. Sharing your
lunch is like a covalent bond (Fig. 3), someone
stealing your lunch is a dative covalent bond!
In a similar way, Stephen Hawking used over 70 analogies in his book A Brief History of Time in order to explain
astrophysics.
1
This raises an important point. It is essential with any analogy to be sure that the analog is familiar to your own students. So you might use soccer with some boys, but rugby
with others; and use netball with some girls and soccer with
others.
2
Of course the Bohr-Rutherford model is not the currently
accepted scientific view of the structure of the atom, but the
example illustrates the use of analogy in knowledge generation and understanding.
3
There are a number of other well-documented scientific
discoveries that have used analogy to advance science;
probably the best known chemistry example is Kekulé’s
model of snakes biting their tails to understand the structure
of the benzene ring.
4
Fig. 3: Sharing lunch is like a covalent bond [above]
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