Amy was a participant in the Understanding Science Project. She was interviewed when she had just started her 'A level' (i.e. college) chemistry, and one of the topics that the course had started with was mass spectrometry – (see A dusty analogy – a visual demonstration of ionisation in a mass spectrometer). Amy seemed to be unconvinced, or at least surprised by a number of aspects of the material she had learnt about the mass spectrometer.
So, for example, she found it strange that iron could be vaporised:
So which bits of that are you not convinced about then?
(Pause, c.3 seconds)
It just all … I don't, it's not that I'm not convinced about it, it's just sound strange, because it's like…
(Pause, c.2s)
… erm, well this sounds like ridiculous but, like but before today like none of the people in out class had thought about iron being turned into a gas, and it's little things like that which sound weird.
Okay, erm so if you said to people, can you turn water into a gas, most people would say.
Yeah.
Yeah, do it in the kettle all the time, sort of thing.
Yeah.
But if you said to people can you turn iron into a gas? – do people find that a strange idea?
Yeah.
Yeah?
Well we did. (She laughs)
Although Amy and her classmates had studied the states of matter years earlier at the start of secondary school, and would have learnt that substances can commonly be converted between solid, liquid and gaseous phases, their life-world (everyday) experience of iron – the metallic material – made the idea of iron vapour seem 'weird'.
Given the prevalence of grounded learning impediments where prior learning interferes with new learning, this did not seem as "ridiculous" to the interviewer as Amy suspected it may appear.
As science teachers we have spent many years thinking in terms of substances, and the common pattern that a substance can exist as a solid, liquid or gas – yet most people (even when they refer to 'substances') usually think in terms of materials, not substances. Iron, as a material, is a strong solid material suitable for use in building structures – thinking of iron the familiar material as becoming a gas requires a lot of imagination for someone who not habitually think in terms of scientific models.
Although Amy thought her classmates had found the idea of iron as gas as weird, they had not rejected it. Yet, if it is such a counter-intuitive idea, it may not be later readily brought to mind when it might be relevant, unless it is consolidated into memory by reinforcement through being revisited and reiterated. (Indeed the research interview provides one opportunity for rehearsing the idea: research suggests that whenever a memory is activated this strengthens it.)
Mohammed was a participant in the Understanding Science Project. When interviewed in the first term of his upper secondary (GCSE) science course (in Y10), he told me he had been learning about ionic bonding in one of his science classes. Mohammed had quite a clear idea about ionic bonding, which he described in terms of the interactions of two atoms where "they both want to get full outer shells", leading to salt which was "like two atoms joined together":
The "two atoms joined together" sounds much like a molecule (and it is very common for students to identify molecule like ion-pairs even in representations of extensive ionic lattices), so I asked Mohammed about this:
Can I see these atoms?
No. They're really small. Because the wavelength of visible light is actually too like large to see the atoms, they just pass over them.
Okay, so I can't see them. But I can imagine them, can I?
Yeah.
So if I could imagine a sodium atom and chlorine atom, and then they form salt, what would it look like afterwards? How could I imagine it afterwards.
Oh it's like two atoms joined together.
That sounds like a molecule to me?
It's not actually, like, joined.
No?
Because I know that whenever things of opposite charge, I know two rods, when they come together, they don't actually touch, so they don't exactly touch, but they are very close, two atoms close to each other
So a molecule would be different to that in some way, would it?
Yeah, a molecule's actually bonded
So how that different?
I think in a molecule, the electron actually slots into spaces.
I see, and it doesn't do that in this case?
No.
So Mohammed thinks that the interaction between the ions will be due to their electrical charges, but, for him, this may not count as a bond, as the forces just hold the ions ("atoms") close together, and do not actually join them. Mohammed's idea of the atoms not actually touching, "they don't actually touch, so they don't exactly touch", is transferring a notion from the familiar world of macroscopic phenomena (where things touch, or they do not touch) to the submicroscopic world of quanticles that do not have definitive size/volume, and do not actually have distinct surfaces, so touching is a matter of degree. There is no more (or less) 'touching' in a covalent bond than in ionic bonding. So according to Mohammed the ions do not form a molecule, as in a molecule there would some kind of more direct joining – he suggests something like an interlocking with electrons from one atom slotting into spaces on another.
Interestingly, Mohammed bases his notion that the ions would not touch on a general principle that he considers to apply whenever considering things of opposite charge – which he justifies on his knowledge that "two [charged] rods, when they come together, they don't actually touch". He may be misremembering something here – or he may have seen a demonstration of suspended charged rods of the same material (so either both negatively or both positively changed) that when one is moved closer to the other the rods repel. Whatever the source, Mohammed seems to feel he has a valid general principle that he can apply here that act as a grounded learning impediment channelling his thinking about the case under discussion along 'the wrong lines'.
Mohammed's notion of the ionic bonding as being just due to forces rather than being a proper bond is very similar to a common alternative conceptions of ionic bonding which sees ions in a lattice only having a limited number of ionic bonds depending upon valency (the valency conjecture) but bonded with other coordination counter-ions by 'just forces' (the just forces conjecture) – although here Mohammed suspected that all ionic bonding fell short of being proper chemical bonds.
This is a very mechanical model of the covalent bond, whereas the scientific model presents bonding as more of a process than a material mechanical link. However teaching models often present bonding this way, and sometimes molecules are modelled in terms of jigsaws with atoms or radicals as pieces to be slotted together. Although such models are only meant to provide a simple analogy for the bonding they may act as learning impediments if learners take them too 'literally' as realistic representations and transfer inappropriate associations from the model to their understanding of the system being modelled.
Mohammed also uses similar language when asked about salt dissolving in water, as the charge of the water forces the sodium and chlorine ions to slot into certain places within the water molecules *.
Sophia was a participant in the Understanding Science Project. In Y7, Sophia had told me that if molten iron was heated "some of it would evaporate but not all of it, 'cause it's not like water and it's more heavy". She thought only "a little" of the iron would evaporate to give iron vapour: The rest "really just stays as a liquid". [See 'Iron is too heavy to completely evaporate'.]
Just over a year later (in Y8) Sophia had been studying "that different erm substances have different freezing and melting and boiling points, and some aren't like a liquid at room temperatures, some are a solid and some are a gas and things like that".
Give me an example of something else that's a solid at room temperature?
Iron.
Do you think iron would have a melting point?
Yeah.
Yeah, and if I, what would I get if I, if I heated iron to its melting point?
It would become a liquid.
And why would it do that?
Because it's got so hot that particles – they have spread out or something?
So what do you think would happen if I heated the iron liquid?
It would stay a liquid.
No matter how much I heated it?
It might, I don't know if it would become a vapour.
Can you get iron vapour?
No, I don't think so.
You don't think so?
No.
So it seems that Sophia had shifted from accepting that iron would partially evaporate (when learning about the particle model of the different states), to considering that iron (probably) can not become a vapour. The notion of iron as a gas is not something we can readily imagine, and apparently did not seem very feasible. In part this might be because we think of iron the material (a metal, which cannot exist in in the vapour phase) rather than as a substance that can take different material forms.
It seems Sophia's prior knowledge of iron the material was working against her learning about iron the substance, an examples of a grounded learning impediment where prior knowledge impedes new learning.
In Y7 Sophia had seemed to have a hybrid conception where having been taught a general model of the states of matter and changes of state, she accepted the counter-intuitive idea that iron could evaporate, but thought that (unlike in the case of water) it could not completely evaporate . This might have been a 'stepping stone' between not accepting iron could be in the gaseous state and fitting it within the general model that all substances will when progressively heated first melt and then evaporate (or boil) as long as they did not decompose first.
However, it seems that a year later Sophia was actually more resistant to the idea that iron could exist as vapour and so now she thought molten iron would remain liquid no matter how much it was heated. If anything, she had reverted to a more intuitive understanding. This is not that strange: it has been shown that apparent conceptual gains which are counter to strongly held intuitions that are brought about by teaching episodes that are not regularly reinforced can drop away as the time since teaching increases. Conceptual change does not always involve shifts towards the scientific accounts.
[Sophia was in lower secondary school when I talked to her about this: but I was also told by a much older student that the idea of iron turning into a gas sounds weird.]
One of the things I have noticed in recent news reports about the current pandemic is the tendency to justify our susceptibility to the COVID-19 coronavirus by praising the virus. It is an intelligent and sneaky foe, and so we have to outwit it.
But no, it is not. It is a virus. It's a tiny collection of nucleic material packaged in a way that it can get into the cells which contain the chemical resources required for the virus to replicate. It is well suited to this, but there is nothing intelligent about the behaviour. (The virus does not enter the cell to reproduce any more than an ice cube melts to become water; or a hot cup of coffee radiates energy to cool down; or a toddler trips over to graze its knee rather than because gravity acts on it.) The virus is not clever nor sneaky. That would suggest it can adapt its behaviour, after reflecting upon feedback from its interactions with the environment. It cannot. Over generations viruses change – but with a lot of variations that fail to replicate (the thick ones in the family?)
Yet any quick internet search finds references to the claimed intellectual capacities of these deadly foes. Now of course an internet search can find references to virtually anything – but I am referring to sites we might expect to be authoritative, or at least well-informed. And this is not just a matter of a hasty response to the current public health emergency as it is not just COVID 19, but, it seems, viruses generally that are considered intellectually superior.
Those smart little viruses
The site Vaccines Today has a headline in a posting from 2014, that "Viruses are 'smart', so we must be smarter", basing its claims on a lecture by Colin Russell, Royal Society University Research Fellow at Cambridge University. It reports that "Dr Russell says understanding how 'clever' viruses are can help us to outsmart them". (At least there are 'scare quotes' in some of these examples.)
An article from 2002 in an on-line journal has the title "The contest between a clever virus and a facultatively clever host". Now I have moaned about the standard of many new internet journals, but this is the Journal of the Royal Society of Medicine, and the article is in volume 95, so I think it is safe to apply the descriptor 'well-established' to this journal.
A headline in Science news for Students (published by Society for Science & the Public) from 2016 reads "Sneaky! Virus sickens plants, but helps them multiply". I am sure it would not take long to find many other examples. An article in Science refers to a "nasty flu virus".
Sneaky viruses
COVID-19 is a sneaky virus according to a doctor writing in the Annals of Internal Medicine. Quite a few viruses seem to be sneaky – the the human papillomavirus is according to an article in the American Journal of Bioethics. The World Health Organisation considers that a virus that causes swine fever, H1N1, is sneaky according to an article in Systematic Reviews in Pharmacy, something also reported by the BMJ.
There are many references in the literature to clever viruses, such as Epstein‐Barr virus according to a piece in the American Journal of Transplantation. The Hepatitis C virus is clever according to an article in Clinical Therapeutics.
Science communication as making the unfamiliar, familiar
Science communication is a bit like teaching in that the purpose of communication is often to be informative (rather than say, social cohesion, like a lot of everyday conversation {and, by the way,it was another beautiful day here in Cambridgeshire today, blue sky – was it nice where you are?}) and indeed to make the unfamiliar, familiar. Sometimes we can make the unfamiliar familiar by showing people the unfamiliar and pointing it out. 'This is a conical flask'. Often, however, we cannot do that – it is hard to show someone hyperconjugation or hysteresis or a virus specimen. Then we resort to using what is familiar, and employing the usual teacher tricks of metaphor, analogy, simile, modelling, graphics, and so forth. What is familiar to us all is human behaviour, so personification is a common technique. What the virus is doing, we might suggest, is hijacking the cell's biochemical machinery, as if it is a carefully planned criminal operation.
Strong anthropomorphism and dead metaphors
This is fine as far as it goes – that is, if we use such techniques as initial pedagogic steps, as starting points to develop scientific understanding. But often the subsequent stage does not happen. Perhaps that is why there are so many dead metaphors in the language – words introduced as metaphors, which over time have simple come to be take on a new literal meaning. Science does its fair share of borrowing – as with charge (when filling a musket or canon). Dead metaphors are dead (that is metaphorical, of course, they were never actually alive) because we simply fail to notice them as metaphors any more.
There are probably just as many references to 'clever viruses' referring to computer viruses as to microbes – which is interesting as computer viruses were once only viruses metaphorically, but are now accepted as being another type of virus. They have become viruses by custom and practice, and social agreement.
Whoever decided to first refer to the covalent bond in terms of sharing presumably did not mean this in the usual social sense, but the term has stuck. The problem in education (and so, presumably, public communication of science) is that once people think they have an understanding, an explanation that works for them, they will no longer seek a more scientific explanation.
So if the teacher suggests an atom is looking for another electron (a weak form of anthropomorphism, clearly not meant to be taken too seriously – atoms are not entities able to look for anything) then there is a risk that students think they know what is going on, and so never seek any further explanation. Weak anthropomorphism becomes strong anthropomorphism: the atom (or virus) behaves like a person because it has needs and desires just like anyone else.
Perhaps in our current situation this is not that important – the public health emergency is a more urgent issue than the public understanding of the science. But it does matter in the long term. Viruses are not clever – they have evolved over billions of years, and a great many less successful iterations are no longer with us. The reason it matters is because evolution is often not well understood.
As an article in Evolution News and Science Today (a title that surely suggests a serious science periodical about evolution) tells us again that "Viruses are, to all appearances, very clever little machines" and asks "do they give evidence of intelligent design" (that is, rather than Darwinian natural selection, do they show evidence of having an intelligent designer?) After exploring some serious aspects of the science of viruses, the article concludes: "So it seems that viruses are intelligently designed" – that is, a position at odds with the scientific understanding that is virtually a consensus view based on current knowledge. Canonical science suggests that natural processes are able to explain evolution. But these viruses are so clever they must surely have been designed (Borg technology, perhaps?)
This is why I worry when I hear that viruses are these intelligent, deliberate agents that are our foes in some form of biological warfare. It is a dangerous way of thinking. So, I'm concerned when I read, for example, that the cytomegalovirus is not just a clever virus but a very clever virus. Indeed, according to an article in Cell Host & Microbe "CMV is a very clever virus that knows more about the host immune system and cell biology than we do". Hm.
1. The subheading was amended on 4th October 2021, after it was quite rightly pointed out to me that the original version, "COVID-19 is not a clever or sneaky virus (but it is not dumb either)", incorrectly conflated the disease with the virus.
In a sponge, the particles are spread out more, so it can absorb more water
Keith S. Taber
Morag was a participant in the Understanding Science Project. In her first term of secondary school, she told me that he had learnt about particles. Morag had explained, and simulated through role play for me, the arrangements of particles in the different states of matter (See: So if someone was stood here, we'd be a solid.) She had also emphasised just how tiny the particles were, "little, little-little-little things", and so how many there were in a small object: "millions and millions and millions". This suggested she had accepted and understood the gist of the scientific model of submicroscopic particles.
Yet as the conversation proceeded, Morag suggested the macroscopic behaviour of sponge in absorbing water could be explained by the arrangement of particles leaving space for the water. This is perhaps a reasonably, indeed quite imaginative, suggestion at one level, except that the material of a sponge is basically solid (where, as Morag recognised, that the particles would be very close together). A sponge as whole is more like a foam, with a great volume of space between the solid structure (where air can be displaced by liquid) and an extensive surface area.
Do you think it is important to know that everything is made of particles?
No.
It's not important?
Well it could be important, but it's not that important. Well, you see, like that [indicating the voice recorder used to record the interview] has got like lots and lots of particles pushed together this [Morag gestures]…But a sponge, the particles are like, the particles are more kind of like, they're still the same, but it's just spread out more, so it can absorb more water.
Oh I see, so are you saying that the same particles are in my little recorder, as in the sponge.
Yeah, they're the same, but there's just more of them in one than there would be in the other.
The failure here is perhaps less Morag's inappropriate explanation, than the tendency to teach about the ideals of solids, liquids and gases, which strictly apply only to single substances, where most real materials students come across in everyday life are actually mixtures or composites where the labels 'solid', liquid' and 'gas' are – at best – approximations.
Teaching has to simplify complex scientific ideas to make them accessible to students of different ages, so often teaching models are used. But sometimes simplifications can cause misunderstandings, and so the development of alternative conceptions. If 'everything is a solid, liquid or gas' is used as a kind of teaching model, or even presented as a slogan or motto for students to echo back to the teacher, when lots of things students come across in everyday life (e.g., butter, clouds, the pet cat – a bathroom sponge) do not easily fit these categories, and this is likely to lead to students overgeneralising.
Although it is often not possible to assign a single simple cause to a student's flawed thinking, this could be considered likely to be an example of a pedagogic learning impediment (a type of grounded learning impediment) in chemistry: a case where an approach to teaching can lead students' thinking in unhelpful directions.
Electrons from different elements would be different – perhaps because they would actually contain some of the element in the electron?
Keith S. Taber
Annie was a participant in the Understanding Chemical Bonding project. She was interviewed near the start of her college 'A level' course (equivalent to Y12). She was shown a representation of a tetrachlomethane molecule.
When Annie was asked about the diagram, she noted that (following a representational convention) the electrons were represented differently. Using different symbols like this is quite common, but is little more that a bookmaking tool – to help keep count of the number of electrons in the molecule in relation to those that would be present in discrete atoms.
…are there any bonds [shown] in that diagram do you think?
Yes.
How many?
Four.
Four bonds, so we've got four bonds there. Erm, are the bonds actually shown?
Yeah.
So how are they represented on the diagram?
By the circles that overlap, and they're showing it by the electrons, the outer-shell electrons in the chlorine have got black dots and the ones from carbon have got just circles.
Okay. So the carbon electrons and the chlorine electrons are signified in a different way
Yeah.
I followed up this point to check Annie understood that the convention did not imply that there was any inherent difference between the electrons.
So what would be the difference between a carbon electron and a chlorine electron?
(pause, c.5s)
The expected answer here was 'no difference', but the pause suggested Annie was not clear about this. So I set up an imaginary scenario, a kind of thought experiment:
If I gave you a bottle of electrons – which I can't do – how would you be able to tell chlorine electrons from carbon electrons – in what ways would they be different?
They would be different because, erm, I don't know if they would actually contain some of the element in the electron.
Do you think they might have little labels on some with "C"s and some with "Cl"s or
Yeah, I don't know if you got an electron, and you could sort of if you took one single one you could say, right that's chlorine and that one's carbon.
You are not sure, you are not sure if you could, or not?
No.
The idea that an electron might contain some of the element seems to miss the key idea that macroscopic phenomena (samples of element) are considerer to energy from extensive ensembles of submicroscopic particles ('quanticles').
Annie did not seem too sure here – perhaps her intuition was that a carbon electron would be different to a chlorine electron, but she could not suggest how. Electrons have no memories, and there is no way of knowing whether an electron has previously been part of a particular atom (or ion or molecule). A free electron is not meaningfully a chlorine electron or a carbon electron. However, students do not always appreciate this, and may consider that free electrons in some sense belong to an atoms they they derived form, and even that this may later have consequences (as with the 'history' conjecture in thinking about ionic bonding).
Dissolving salt is a chemical change as you cannot turn it back as it was before
Keith S. Taber
Sandra was a participant in the Understanding Science Project. When I interviewed Sandra about her science lessons in Y7 she told me "I've done changing state, burning, and we're doing electricity at the moment". I asked her about burning:
Well, tell me a bit about burning then. What's burning then? It's just when something gets set on fire, and turns into ash, or – has a chemical change, whatever. Has a chemical change: what's a chemical change? It means something has changed into something else and you can't turn it back. Oh I see. So burning would be an example of that. Yeah.
So far this seemed to fit 'target knowledge'. However, Sandra suggested that dissolving would also be a chemical change. Dissolving is not normally considered a chemical change in school science, but a physical change, the distinction is a questionable teaching model. (Chemical change is said to involve bond breaking/making, and of course dissolving a salt does involve breaking up the ionic bonding to form solvent-solute interactions.)
Are there other examples? Erm – dissolving. So give me an example of something you might dissolve? Salt. Okay, and if you dissolve salt, you can't get it back? Not really, not as it was before. No. Can you get it back at all? Sort of, you can like, erm, make the, boil the water so it turns into gas, and then you have salt, salt, salt on the, left there. Sometimes. But you think that might not be quite the same as it was before? No. No. Different in some way? Yeah How might it be different? Be much smaller. Oh I see, so do you think you'd have less salt than you started with? You'd have the same, but there would just be more particles, but they'd be smaller. Ah, so instead of having quite large grains you might have lots of small grains Yeah.
So Sandra was clear that one could dissolve salt, and then reclaim the same amount of salt by removing the solvent (water) which from the canonical perspective would mean the change was reversible – a criterion of a physical change.
Yet Sandra also thought that although the amount of salt would be conserved, the salt would be in a different form – it would have different grain size. (Indeed, if the water was boiled off, rather than left to evaporate, it might indeed be produced as very small crystals.)
So, Sandra seemed to have a fairly good understanding of the process, but because of the way she interpreted the criterion of a chemical change, something [salt] has changed into something else [solution] and you can't turn it back [with the same granularity]. Large grains will have changed into small grains – so this would, to Sandra's mind, be a chemical change.
Science teachers deserve a great deal of public appreciation. A teacher can teach something so that a student learns it well – and yet still form an alternative conception – here because of the inherent ambiguity in the ways language is used and understood. Sandra's interpretation – if you start off with large particles and end up with smaller particles then you have not turned it back – was a reasonable interpretation of what she had learnt. (It also transpired there was ambiguity in quite what was meant by particles.)
Amy was a participant in the Understanding Science Project. When I had talked to Amy when she was in Y10 she had referred to things being bonded: "where one thing is joined on to another thing, and it can be chemically bonded" and how "in a compound, where two or more elements are joined together, that's an example of chemical bonding".
The following year, in Y11, when she was studying fats she talked about "how they're made up and like with all the double bonds and single bonds" where a double bond was "where there are kind of like two bonds between erm carbon atoms instead of like one" and a bond was "how two atoms are joined together". Later in Y11, Amy told be that she did not know how to explain chemical bonding, but "in lessons like we've always been shown these kind of – things – where you kind of, you've got the atom, and then you've got the little, grey stick things which are meant to be the bonds, and you can just – fit them together."
As Amy had told me "everything is made up of atoms", I provocatively asked her if the chemical bond was made of atoms. Amy had "absolutely no idea" but she "suppose(d) it would have to be, wouldn't it".
Not only is this an alternative conception, but to a chemist, or science teacher, the idea that chemical bonds are themselves made up of atoms seems incongruous and offers a potential for infinite regress (are those atoms in the bonds, themselves bonded? If so, are those bonds also made of atoms?)
This alternative conception could be considered a kind of associative learning impediment – that is where a learner makes an unintended link and so applies an idea outside of its range of application. All material is considered to be made of atoms – or at least quanticles comprising one of more nuclei bound to electrons (i.e., ions, molecules). Even this is not an absolute: the material formed immediately after the big bang was not of this form, and nor is the matter in a neutron star, but the material we usually engage with is considered to be made of atom-like units (i.e., ions, molecules).
But to suggest that Amy has made an inappropriate association seems a little unfair. Had Amy thought "all matter was made of atoms" and then suggested that chemical bonding was made of atoms this would be inappropriate as chemical bonding is not material but a process – electrical interactions between quanticles. Yet it is hard to see how one can over-extend the range of 'everything', as in "everything is made up of atoms".
There is an inherent problem with the motto everything is made up of atoms. It is probably something that teachers commonly say, and think is entirely clear – that it is obvious what its scope is – but from the perspective of a student there is not the wealth of background knowledge to appreciate the implied limits on 'everything'.
Learners will readily pick up teaching mottos such as "everything is made of atoms" and take them quite literally: if everything is made of atoms then bonds must be made of atoms. So although she was wrong, I think Amy was just applying something she had learnt.
I followed up on Amy's use of the term 'compound' to explore how she understood the term:
How would you define a compound?
Erm …Something which has erm two or more elements chemically bonded.
… So you give me an example of that, compound?
Erm, sodium oxide.
Sodium oxide, okay, so there are two or more elements chemically bonded in sodium oxide are there?
Uh hm
And what would those two or more elements be?
Sodium and oxygen.
Okay. Erm, so when we say sodium oxide is chemically bonded, what we are saying there is?
[pause, c 2s]
Erm – a sodium atom has been bonded with a oxygen atom to form erm a new substance.
So Amy's example of a compound was sodium oxide, which would normally be considered essentially an ionic compound, that is a compound with ionic bonding. So this gave me an opportunity to test out whether Amy saw the bonding in sodium chloride and sodium oxide as similar.
Okay, so that was chemical bonding,
Mm.
and that occurs with compounds?
Yeah.
And what did you say about ionic bonding?
Erm, it's the outer electrons they are transferred from one element to another.
Now what does that occur in? You gave me one example, didn't you?
Uh huh
Sodium chloride?
Yeah …
Erm. Would sodium chloride be er an element?
[pause, c.2s]
Sodium chloride, no.
No?
It would be a compound.
You think that would be a compound?
Yeah.
And a compound is two or more elements joined together by chemical bonding?
Yeah.
So Amy had told me that sodium chloride, which had ionic bonding, was (like sodium oxide) a compound, and she had already told me that a compound comprised of "two or more elements chemically bonded", so it should be follow that sodium chloride (which had ionic bonding) had chemical bonding.
Do you think sodium chloride has chemical bonding?
Er – I think so
And it also has ionic bonding, or is that the same thing?
Erm,
[pause, c.2s]
I dunno, I've never thought about it that way, erm,
[pause c.3s]
I'm not sure, erm
[pause, c.2s]
I dunno, it might be.
Clearly, whatever Amy had been taught (and interviewing students reveals they often only recall partial and distorted versions of what was presented in class) she had learnt
(1) that ionic bonding was transfer of electrons (an alternative conception) as in the example of sodium transferring an electron to chlorine; and that
(2) a compounds was where two or more elements chemically bonded together, and an example was sodium oxide where the elements sodium and oxygen were chemical bonded.
Yet these two pieces of learning seemed to have been acquired as isolated ideas without any attempt to link them. Initially Amy seemed to feel ionic bonding and chemical bonding were quite separate concepts.
When taken through an argument that led to her telling me that sodium chloride, that she thought had ionic bonding, was a compound, which therefore had chemical bonding, there should have been a logical imperative to see that ionic bonding was chemical bonding (actually, a kind of chemical bonding – as the logic did not imply that chemical bonding was necessarily ionic bonding). Despite the implied syllogism:
sodium chloride has ionic bonding
sodium chloride is a compound
compounds have elements chemically bonded together
therefore ionic bonding …
Amy was unsure what to deduce, presumably because she had seen the two concepts of ionic bonding and chemical bonding as discrete notions and had had given no thought to a possible relationship between them. However explicit teaching had been on this point, it is very likely that the teacher had expected students to appreciate that ionic bonding was a type of chemical bonding – but Amy had not integrated these ideas into a connected conceptual structure (i.e., there was a learning bug that could be called a fragmentation learning impediment).
Amy was a participant in the Understanding Science Project. The first time I talked to Amy, near the start of her GCSE 'triple science' course in Y10 she told me that "in normal chemistry (i.e., the chemistry part of 'double science', as opposed to the optional additional chemistry lesson as part of 'triple science' that Amy also attended) we're doing about ionic bonding" which she understood in terms of "atoms which have either lost or gained electrons so they are either positively or negatively charged" because "in ionic bonding it's the electrons that are transferred".
When asked other examples of ionic bonding apart from sodium and chlorine Amy told me "That's the one I did".
To a teacher it seems inherently obvious that ionic bonding is type of bonding – in much the way that a snare drum is a kind of drum or a conscientious student is a type of student. However, this may not always be obvious to students (even the conscientious ones).
When I asked Amy about bonding she referred to things being chemically bonded, and when I asked if ionic bonding was the same as chemical bonding, she was not sure how these concepts were related:
So what exactly is bonding?
Erm, where er one thing is joined on to another thing, and it can be chemically bonded or, yeah {laughs}
So we can talk about chemical bonding?
Mm.
Are there other types of bonding then?
Erm, there must be, if there's chemical bonding, I'm not sure, erm
[pause, c.5s]
But we talk about chemical bonding,
Mm.
and we talk about ionic bonding. So is ionic bonding the same thing as chemical bonding or is there a difference?
Erm, in, well in chemical bonding, erm like in a compound, where erm – two or more elements are joined together, that's an example of chemical bonding, but in – erm – ionic bonding it's the erm electrons that are transferred. [pause, c.2s] I think.
It seems Amy had been taught about chemical bonding and had learn about this as "a compound, where two or more elements are joined together", and she had been taught about ionic bonding and had learnt that this was where "the electrons are transferred".
Ionic bonding is not (and need not be associated with) electron transfer. It is not possible form talking to Amy to now exactly what her teacher told her – clearly she could have misunderstood or forgotten material form class. It is possible that it was made clear that ionic bonding was one type of chemical bonding, but Amy either missed that point or did not now recall it. It is also possible is was not made explicit but was assumed to be obvious (especially if ionic bonding had been presented as part of a sequence on chemical bonding. Sadly, what is obvious to teachers is not always obvious to learners, and indeed I've seen in my interviews that students are not always clear when one topic has finished and another has started. There is no sense here that I wish to criticise the teacher (who for all I know gave an exemplary presentation of the chemical bonding), but would simply suggest that when teaching one can never assume what should be obvious is obvious and that it is probably difficult to be too explicit about key ideas, or to reiterate them too often!
So at this point it seemed Amy only knew one example of ionic bonding, sodium chloride, and did not associate this with compounds which had chemical bonding. This could be considered a fragmentation learning impediment – a failure to make a link that was expected from the teaching. I went on to ask her for an example of a compound, and a she told me about sodium oxide I thought this was an opportunity to probe at the association between ionic boding and chemical bonding a little more.
Amy was a participant in the Understanding Science Project. The first time I talked to Amy, near the start of her GCSE 'triple science' course in Y10 she told me that "in normal chemistry (i.e., the chemistry part of 'double science', as opposed to the optional additional chemistry lesson as part of 'triple science' that Amy also attended) we're doing about ionic bonding" which was "atoms which have either lost or gained electrons so they are either positively or negatively charged" and
"how the outer electron's transferred…to complete the outer shell of the erm chlorine, thing, ion…and the sodium atom loses erm, one electron is it, yeah one electron, erm, which the chlorine atom gains, and that yeah that completes its outer shell and makes the sodium positively charged and the chlorine negatively charged".
Amy told me that "in ionic bonding it's the electrons that are transferred, I think."
So Amy had acquired a common alternative conception, i.e. that ionic bonding involved electron transfer, and that this occurs to atoms to complete their electron shells.
Ionic bonding refers to the forces between ions that hold the structure of an ionic substance together, rather than a mechanism by which such ions might hypothetically be formed – yet often learners come away form learning about ionic bonding identifying it with a process of electron transfer between atoms instead of interactions between ions which can be used to explain the properties of ionic substances.
Moreover, the hypothetical electron transfer is a fiction. In the case of NaCl such an electron transfer between isolated Na and Cl atoms would be energetically unfavourable, even if reactants containing discrete atoms were available (which is unrealistic).
Whether students are taught that ionic bonding is electron transfer is a moot point, but often introductory teaching of the topic focuses not on the nature of the bonding, but on presenting a (flawed) teaching model of how the ions in the ionic structure could form by electron transfer between atoms. As this mechanism is non-viable, and so not an authentic scientific account, it may seem odd that teachers commonly offer it.
One explanation may simply be custom or tradition has made this an insidious alternative conception. Science teachers and textbooks have 'always' offered the image of electron transfer as representing ionic bonding. So, this is what new teachers had themselves been taught at school, is what they often see in textbooks, and so what they learn to teach.
Another possible explanation is in terms of what what is known as the atomic ontology. This is the idea that the starting pint for thinking about chemistry at the submicroscopic level is atoms. Atoms do not need to be explained (as if in nature matter always starts as atoms – which is not the case) and other entities such as ions and molecules do need to be explained in terms of atoms. So, the atomic ontology is a kind of misleading alternative conceptual framework for thinking about chemistry at the submicroscopic level.
Current only slows down at the resistor – by analogy with water flow
Keith S. Taber
Students commonly think that resistance in a circuit has local effects, and in part that is because forming a mental model of what is going on in circuits is very difficult. Often models and analogies can be useful. However when an analogy is used in teaching there is also the potential for it to mislead.
Amy was a participant in the Understanding Science Project. Amy (when in Y10) told me she had been taught to use a water flow analogy for electric current. However, because her visualisation of what happens in water circuits was incorrect, she used the analogy to inform an alternative conception about circuits:
Do you have any kind of imagined sort of idea, any little mental models, about what (the flow of electricity round the circuit) might look like? Do you have a way of imagining that?
Erm, yeah, we've been taught the water tank and pipe running round it. … just imagine the water like flowing through a pipe, and obviously like, if the pipe becomes smaller a one point, erm, the water flow has to slow down, and that's meant to represent the resistance of something.
So, so if I had my water, er, tank and I had a series of pipes, they'd be water flowing through the pipes, and if I had a narrower pipe at one point, what happens then?
The water would have to slow down.
So would it slow down just as it goes through the narrow pipe, or would it slow down all the way round?
Erm – just through that part.
(Amy does not appreciate the implications of conservation of mass {that is, the continuity principle} here – at steady state there cannot be a greater mass flow at different points in the circuit).
…
And so how do you imagine that's got to do with resistance, how does that help you understand resistance?
…well resistance, it slows the current down, but then erm, once it passes a resistor or something it, the current is free to flow through the wire again
Analogies can be very useful teaching tools, but when using them it is important to check that the students already understand the features of the analogue that are meant to be helpful. It is also important to ensure that they understand which features are meant to be mapped onto the target system they are learning about, and which are not relevant.
Analogies are only useful when the learner has a good understand of the analogue. In this case, as Amy did not appreciate that the water flow throughout the system would be limited by the constriction, she could not use that as a useful analogy for why a resistor influences current flow at all points in a series circuit. This is an example of where a teaching model meant to support learning, which actually misleads the learner. That is, for Amy, with her flawed understanding of fluid flow, the teaching model acted as a pedagogic learning impediment – a type of grounded learning impediment.
