Keith S. Taber
I have designed a simple concept cartoon. Concept cartoons are used in teaching, usually as an introductory activity to elicit students' ideas about a topic before proceeding to develop the scientific account. This can be seen as 'diagnostic assessment' or just part of good pedagogy when teaching topics where learners are likely to have alternative conceptions. (So, in science teaching, that means just about any topic!)
But I am retired and no longer teach classes, so why am I spending my time preparing teaching resources?
Well, I was writing about dialogic teaching, and so devised an outline lesson plan to illustrate what dialogic teaching might look like. The introductory activity was to be a concept cartoon, so I thought I should specify what it might contain – and so then I thought it would help a reader if I actually mocked up the cartoon so it would be clear what I was writing about. That led to:
A concept cartoon provides learners with several competing ideas to discuss (This can be downloaded below)
What happens, and why?
In my concept cartoon the focal question is what will happen when some NaCl is added to water – and why? This is a concept cartoon because there are several characters offering competing ideas to act as foci for learners to discuss and explore. Of course, it is possible to ask learners to engage with a cartoon individually, but they are intended to initiate dialogue between learners. So by talking together learners will each have an audience to ask them to clarify, and to challenge, their thinking and to ensure they try to explain their reasoning.
Of course, there is flexibility in how they can be used. A teacher could ask students to consider the cartoon individually, before moving to small group discussions or whole class discussion work. (It is also possible to move from individual work to pairing up, to forming groups from two pairs, to the teacher then collating ideas from different groups.) During this stage of activity the intention is to let student make their thinking explicit and to consider and compare different views.
Of course, this is a prelude to the teacher persuading everyone in the class of the right answer, and why it is the right answer. Concept cartoons are used where we know student thinking is likely to make that stage more than trivial. Where learners do already have well-entrenched conceptions at odds with the scientific models, we know simply telling them the target curriculum account is unlikely to lead to long-term shifts in their thinking.
And even if they do not, they will be more likely to appreciate, and later recall, the scientific account if the ground is prepared in this way by engaging students with the potential 'explanatory landscape' (thinking about what is to be explained, and what explanation might look like). If they become genuinely engaged with the question then the teacher's presentation of the science is given 'epistemic relevance'. (Inevitably the science curriculum consists of answers to the questions scientists have posed over many years: but in teaching it we may find we are presenting answers to many questions that simply have never occurred to the students. If we can get learners to first wonder about the questions, then that makes the answer more relevant for them – so more likely to be remembered later.)
Is there really likely to be a diversity of opinion?
This example may seem fairly straightforward to a science teacher. Clearly NaCl, sodium chloride (a.k.a. 'common salt' or 'table salt') is an ionic solid that will dissolve in water as the ions are solvated by the polar water molecules clustering around them. That should also be obvious to advanced students. (Should – but research evidence suggests not always.)
What about students who have just learned about ionic bonding and the NaCl crystal structure? What might they think?
Surely, we can dismiss the possibility that salt will not dissolve? Everyone knows it does. The sea is pretty salty, and people often add salt to the water when cooking. And as long as learners know that NaCl is 'salt' there should be no one supporting the option that it does not dissolve. After all, there is a very simple logical syllogism to be applied here:
- common salt dissolves in water
- common salt is NaCl
- so NaCl dissolves in water
Except, of course, learners who know both that salt dissolves in water and that it is NaCl still have to bring both of those points to mind, and coordinate them – and if they are juggling other information at the same time they may have reached the 'working memory capacity' limit.
Moreover, we know that often learners tend to 'compartmentalise' their learning (well, we all do to some extent), so although they may engage with salt in the kitchen or dinner table, and learn about salt as NaCl in science lessons, they may not strongly link these two domains. And the rationale offered here by the student in red, that NaCl is strongly bonded, is a decent reason to expect the salt to be insoluble.
Now as I have just made this cartoon up, and do not have any classes to try it out on, I may be making a misjudgement and perhaps no learners would support this option. But I have a sneaking suspicion there might be a few who would!
The other two options are based on things I was told when a teacher. That the solid may dissolve as separate atoms is based on being told by an advanced student that in 'double decomposition' reactions the precipitate was produced when atoms in the solution paired up to transfer electrons. The student knew the solutions reacting (say of potassium iodide and lead nitrate) contained ions, but obviously (to my informant) the ions changed themselves back into atoms before forming new ionic bonds by new electron transfers.
I was quite shocked to have been told that, but perhaps should not have been as it involves two very common misconceptions:
- ionic bonds are formed by electron transfer
- chemical reactions occur between atomic species (assuming 'initial atomicity')
(Moreover, another advanced student once told me that when bonds broke electrons had to go back to their 'own' atom as it would be odd for an atom to end up with someone else's electron! So, by this logic, of course anions have to return electrons to their rightful owners before ironically bonding elsewhere!)
So, I suspect a fair number of students new to learning about ionic bonding might well expect it to dissolve as atoms rather than ions.
As regards the other option, that the salt dissolves as molecules, I would actually be amazed if quite a few learners in most classes of, say, 13-14-year-olds, did not select this option. It is very common for students to think that, despite its symmetrical crystal structure (visible in the model in the cartoon), NaCl really comprises of NaCl units, molecule-like ions pairs – perhaps even seen as simply NaCl 'molecules'.
It becomes the teacher's job to persuade learners this is not so, for example, by considering how much energy is needed to melt NaCl , and the conductivity of the liquid and the aqueous solution. (In my imaginary lesson the next activity was a 'Predict-Observe-Explain' activity involving measuring the conductivity of a salt solution.)
A challenge to science teachers
Perhaps you think the students in your classes would not find this a challenging task, as you have taught them that NaCl is an ionic solid, held together by the attractions between cations and anions? All your students know NaCl dissolves, and that the dissolved species will (very nearly always) be single hydrated ions.
Perhaps you are right, and I am wrong.
Or perhaps you recognise that given that in the past so many students have demonstrated alternative conceptions of ionic bonding (Taber, 1994) that perhaps some of your own students may find this topic difficult.
As I no longer had classes to teach, I am uploading a copy of the cartoon that can be downloaded in case you want to present this to your classes and see how they get on. This is primary for students who have been introduced to ionic bonding and taught that salts such as NaCl form solids with regular arrangements of charged ions. If they have not yet studied salts dissolving then perhaps this would be a useful introductory ability for that learning that content?
If you have already taught them about salts dissolving, then obviously they should all get the right answer. (But does that mean they will? Is it worth five minutes of class-time to check?)
And if you work with more advanced students who are expected to have mastered ionic bonding some years ago, then we might hope no one in the class would hesitate in selecting the right answer. (But can you be sure? You could present this as something designed for younger students, and ask your students how they would tutor a younger bother or sister who was not sure what the right answer was.)
If you do decide to try this out with your students – I would really like to know how you get on. Perhaps you would even share your experience with other readers by leaving a comment below?
Work cited:
- Taber, K. S. (1994) Misunderstanding the ionic bond, Education in Chemistry, 31 (4), pp.100-103.
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