Category: alternative conception

A tangible user interface for teaching fairy tales about chemical bonding

Keith S. Taber

Image by S. Hermann & F. Richter from Pixabay
Once upon a time there was a nometal atom that was an electron short of a full outer shell. "I wish I had an octet" she said, "if only I knew a nice metal atom that might donate their extra electron to me"… Image by S. Hermann & F. Richter from Pixabay

 

Today I received one of those internet notifications intended to alert you to work that you might want to read:

"You wrote the paper A common core to chemical conceptions: learners' conceptions of chemical…. A related paper is available on Academia.

Tangible interaction approach for learning chemical bonding"

an invitation to read
An invitation to read

I was intrigued. Learning (and teaching) about chemical bonding concepts has been a long-standing interest of mine, and I have written quite a lot on the topic, so I clicked-through and downloaded the paper.

The abstract began

"In this paper we present ChemicAble, a Tangible User Interface (TUI) for teaching ionic bonding to students of grade 8 to 10. ChemicAble acts as an exercise tool for students to understand better the concepts of ionic bonding by letting them explore and learn…."

Ionic bonding – an often mislearnt topic

This led to mixed feelings.

Anything that can support learners in making sense of the abstract, indeed intangible, nature of chemical bonding offered considerable potential to help learners and support teachers. Making the abstract more concrete is often a useful starting point in learning about theoretical concepts. So, this seemed a very well-motivated project that could really be useful.

It is sometimes argued that educational research is something of an irrelevance as it seldom impacts on classroom practice. In my (if, perhaps, biased) experienced, this is not so – but it is unrealistic to expect research to bring about widespread changes in educational practice quickly, and arguments that most teachers do not read research journals and so do not know who  initiated particular proposals has always seemed to me to be missing the point. We are not looking for teachers to pass tests on the content of research literature, and it is quite natural that the influence of research is usually indirect through, for example, informing teacher education and development programmes, or through revisions of curriculum, recommended teaching schemes, or formal standards.

This study by Agrawal and colleagues was not a theoretical treatise but a report of the implementation of a tool to support teaching and learning – the kind of thing that could directly impact teaching. So this was all promising.

However,I  also knew only too well that ionic bonding was a tricky topic. When I started research into learners' developing understanding of chemical bonding (three decades ago, now) I read several studies suggesting there were common alternative conceptions, that is misunderstandings, of ionic bonding found among students (e.g., Butts & Smith,  1987).

My own research suggested these were not just isolated notions, but often reflected a coherent alternative conceptual framework for ionic bonding that I labelled the 'molecular' framework (Taber, 1994, 1997). Research I have seen from other contexts since, leads me to believe this is an international phenomenon, and not limited to a specific curriculum context (Taber, 2013).

(Read about 'the Understanding Chemical Bonding project')

Ionic bonding – an often mistaught topic?

Indeed, I feel confident in suggesting:

  • secondary level students very commonly develop an alternative understanding of ionic bonding inconsistent with the scientific account…
  • …which they find difficult to move beyond should they continue to college level chemistry…
  • … and which they are convinced is what they were taught

Moreover, I strongly suspect that in quite a few cases, the alternative, incorrect model, is being taught. It is certainly presented, or at least implied, in a good many textbooks, and on a wide range of websites claiming to teach chemistry. I also suspect that in at least some cases,  teachers are teaching this, themselves thinking it is an acceptable approximation to the scientific account.

(Read about 'The molecular framework for ionic bonding')

A curriculum model of ionic bonding

So, I scanned the paper to see what account of the science was used as the basis for planning this teaching tool. I found this parenthetical account:

"{As stated in the NCERT book on Science for class X, chapter 3, 4, the electrons present in the outermost shell of an atom are known as the valence electrons. The outermost shell of an atom can accommodate a maximum of 8 electrons. Atoms of elements, having a completely filled outermost shell show little chemical activity. Of these inert elements, the helium atom has two electrons in its outermost shell and all other elements have atoms with eight electrons in the outermost shell.

The combining capacity of the atoms of other elements is explained as an attempt to attain a fully-filled outermost shell (8 electrons forming an octet). The number of electrons gained, lost or shared so as to make the octet of electrons in the outermost shell, gives us directly the combining capacity of the element called the valency. An ion is a charged particle and can be negatively or positively charged. A negatively charged ion is called an 'anion' and the positively charged ion, a 'cation'. Metals generally form cations and non-metals generally form anions. Atoms have tendency to complete their octet by this give and take of electron forming compounds. Compounds that are formed by electron transfer from metals to non-metals are called ionic compounds.}"

Agrawal et al., 2013 (no page numbers)

There are quite a few ideas here, and quite a lot of his account is perfectly canonical, at least at the level of description suitable for secondary school, introductory, chemistry. However, sprinkled in are some misleading statements.

So,

Curriculum statement Commentary
"…the electrons present in the outermost shell of an atom are known as the valence electrons."

 Fine
"The outermost shell of an atom can accommodate a maximum of 8 electrons."

This is only correct for period 2.

It is false false for period 1 (2 electrons), period 3 (18 electrons), period 4 (32 electrons), etcetera.
"Atoms of elements, having a completely filled outermost shell show little chemical activity. Of these inert elements, the helium atom has two electrons in its outermost shell and all other elements have atoms with eight electrons in the outermost shell."

Fine – apart from the reference to  "completely filled outermost shell"

Of the noble gases, only helium and neon have full outer shells.

'Atoms' of the heavier noble gases with full outer shells would not atoms, but ions, and these would be extremely unstable – i.e., they could not exist except hypothetically under extreme conditions of very intense electrical fields.
"The combining capacity of the atoms of other elements is explained as an attempt to attain a fully-filled outermost shell (8 electrons forming an octet). The number of electrons gained, lost or shared so as to make the octet of electrons in the outermost shell, gives us directly the combining capacity of the element called the valency."

Hm –  generally the valency can be identified with the difference between an atom's electronic configuration and the 'nearest' noble gas electronic configuration – which would be an octet of valence shell electrons, except in period one.

However,  the equivalence suggested here "a fully-filled outermost shell (8 electrons forming an octet)" is only true for period 2. An octet does not suffice for a full outer shell in period 3 (full at 18  electrons), or in period 4 (full at 32 electrons), etcetera.

And, in the statement, valency is described as being related to the intentions of atoms: "is explained as an attempt to attain…" (and "…electrons gained, lost or shared so as to…") which encourages student misconceptions. [Read about 'Learners' anthropomorphic thinking'.]
"An ion is a charged particle and can be negatively or positively charged. A negatively charged ion is called an 'anion' and the positively charged ion, a 'cation'. Metals generally form cations and non-metals generally form anions." Fine.
"Atoms have tendency to complete their octet by this give and take of electron forming compounds."

This is a common notion, but actually suspect. Some elements have an electron affinity such that the atoms would tend to pick up an electron spontaneously.

However, for an element with a valency of -2, such as oxygen, once it has become a singly charged anion (O–), it will not attract a second electron, so apart from the halogens, this is misleading. The negatively charged O– ion will indeed spontaneously repel/be repelled by a (negatively charged) electron.

Metallic elements have ionisation enthalpies showing that energy has to be applied to strip electrons from them – they certainly do not have a "tendency to complete their octet by this giv[ing]" of electrons.
"Compounds that are formed by electron transfer from metals to non-metals are called ionic compounds."

This is not usually how ionic compounds are formed. Although it is possible in the lab. to use binary synthesis (e.g., burning sodium in chlorine – not for the faint-hearted), that is not how ionic compounds are prepared in industry, or how the NaCl in table salt formed naturally.

(And even when burning sodium in chlorine, neither of the reactants are atomic, so even here there is no simple transfer of electrons between atoms.)

So this account is a mixture of the generally correct; the potentially misleading; and the downright wrong.

Agrawal and colleagues describe an ingenuous apparatus they had put together so that students can physically manipulate tokens to see ionic bond formation represented. This looks like something that younger secondary children would really enjoy.

They also report a small-scale informal evaluation of a classroom test of the apparatus with an unspecified number of students, reporting very positive responses. The children generally found the apparatus easy to use, the information it represented easy to understand, and they thought it helped them learn about chemical [ionic] compound formation.  So this seems very successful.

However, what did it help them learn?

The teaching model

"For example, when a token representing [a] sodium atom is placed on the table top, its valence shell (outermost shell) with 1 revolving valence electron is displayed around the token. When the student places a chlorine atom on the table, its valence shell along with 7 revolving valence electrons is displayed. The electron from the sodium atom gets transferred to the chlorine atom. +1 charge appears on the sodium atom due to loss of electron and -1 charge appears on the chlorine atom due to gain of electron. Both form a stable compound. The top bar on the user interface turns green to show success and displays the name of the stable compound so formed (sodium chloride, in this case). The valence shell of the atoms also turns green to show a stable compound."

Agrawal et al., 2013 (no page numbers)

Which sounds impressive, except NaCl is not formed by electron transfer, and with the ChemicAble the resulting structure is a single Na+-Cl– ion pair, which does not represent the structure of the NaCl compound, and indeed would not be a stable structure.

Does it matter if children are taught scientific fairy tales?

The innovation likely motivated learners. And the authors seem to be basing their 'ChemicAble' on the curriculum models set out in the model science books produced by the Indian National Council of Educational Research and Training. So, the authors have produced something that helps children learn the science curriculum in that context,and so presumably what students will subsequently be examined on. Given that, it seems churlish to point out that what is being taught is scientifically wrong.

So, I find it hard to be critical of the authors, but I do wonder why governments want children to learn scientific fairy tales that are nonsense. The electron transfer model of ionic bonding seems to be popular with teachers, and received well by learners, so if the aim of education is to find material to teach that we can then test children on (so they can be graded, rated, sequences, selected), what is the problem? After all, I am a strong advocate for the idea that what we teach in school science is usually, necessarily, a simplification of the science – and indeed is basically a set of models – and not some absolute account of the universe.

Here the children, the teacher and the researchers have all put a lot of effort into helping learners acquire a scientifically incorrect account of ionic bonding. We think children should learn about the world at the molecular, naometre scale as this is such an important part of chemistry as a science. Yet, to my mind, if we are going to ask children to put time and effort into learning abstract models of the structure of nature at submicroscopic levels, even though we know this is challenging for them, then, although we need to work with simplified models, these should at least be intellectually honest models, and not accounts that we know are completely inauthentic and do not reflect the science. This is why I have been so critical of the incoherence and errors in the chemistry in the English National Curriculum (Taber, 2020).

Otherwise, education is reduced to a game for its own sake, and we may as well ask students to learn random Latin texts, or the plots of Grimms' Fairy Tales, or even the chemical procedures obscured by disguised reagents and allegorical language in alchemical texts, and then test them on how much they retain.

Actually, no, this learning of false models is worse than that, because learning these incorrect accounts confuses students and impedes their learning of the canonical scientific models if they later go on to study the subject further. So, if it is important that children learn something about ionic bonding, let's teaching something that is scientifically authentic and stop offering fairly tales about atoms wanting to fill their shells.

Sources cited:
 
 

 

Chlorine atoms share electrons to fill in their shells

Umar was a participant in the Understanding Chemical Bonding project. When I spoke to him in the first term of his course he was unsure whether tetrachloromethane (CCl4) would have ionic or covalent bonding.

When I spoke to him near the start of his second term, I asked him again about this. Umar then thought this compound would have polar bonding, however he seemed to have difficulty explaining what this meant ⚗︎ . Given his apparently confused notion about the C-Cl bond I decided to turn the conversation to a covalent bond which I knew, well certainly believed, was more familiar to him.

Is it possible for chlorine to form a bond with another chlorine?

[Pause, c.2s]

Yeah.

What substance would you get if two chlorine atoms formed a bond?

[Pause, c.2s]

You get, it still, you get, if you had like two chlorines it depends what groups are attached to it, to see how electronegative or electropositive they are.

What about if you just had two chlorine atoms joined together and nothing else, is that possible?

[Pause, c.3s]

No.

No?

On their own.

Not on their own?

No.

Umar's response here rather surprised me, as I was pretty confident that Umar had met chlorine as an element, and would know it was comprised of diatomic molecules: Cl2.

So you couldn’t have sort of Cl2, a molecule of Cl2?

[Pause, c.1s]

Yeah, you could do.

Could you?

[Pause, c.2s]

They might be just, they might be like, be covalently bonded.

Perhaps the earlier context of talking about polar bonds and the trichloroethane molecule somehow acted as a kind of impediment to Umar remembering about the chlorine molecule. It seemed that my explicit reference to the formula, Cl2, (eventually) activated his knowledge of the molecule bringing to mind something he had forgotten. Although he suggested the bond was (actually "might be") covalent, this seemed less something that he confidently recalled, than something he was inferring from what he could remember – or perhaps even guessing at what seemed reasonable: "they might be just, they might be like, be covalently bonded".

As often happens in talking to learners in depth about their ideas it becomes clear that thinking of students 'knowing' or 'not knowing' particular things is a fairly inadequate way of conceptualising their cognition, which is often nuanced and context-dependent. This suggests that what students respond in written tests should be considered only as what they were triggered to write on that day in response to those particular questions, and may not fully reflect their knowledge and understanding of science topics. Other slightly different questions may well have cued the elicitation of different knowledge. Now Umar had recalled that chlorine comprises of covalent molecules, I asked him about the nature of the bond:

So what would that be, covalently bonded?

They share the electrons.

So how many electrons would they have then?

They’ll have

[Pause, c.7s – n.b., quite a long pause]

like the one on it, the one of the chlorines shares electrons with the other chlorine to fill in its shell on the other one, and the same does it with the other.

In thinking about covalent bonding, Umar (in common with many students) drew upon the full shells explanatory principle that considered bonding to be driven by the needs of atoms to 'fill' their outer electron shells. (The outer shell of chlorine would only actually be 'full' with 18 electrons, but that complication is seldom recognised, as octets and full shells are usually considered synonymous by students).

So how many electrons does each chlorine have to start with?

In the outer shell, seven.

And how many have they got after this?

They’ve got seven, but they share one.

[Pause, c.1s]

Maybe.

So that’s a covalent bond, is it?

Yeah.

So how many electrons are involved in a covalent bond?

[Pause, c.3s]

Erm,

[Pause, c.3s]

Two.

Two electrons.

So where do those two electrons come from?

They like, one that fills up the gap, fills up the – last electron needed in one of the chlorine shells, and the other chlorine shell fills it up in the other one.

So where do they come from?

Each chlorine. Outer shell.

One from each chlorine?

Yeah.

Okay, and that’d be a covalent bond?

Yeah.

Here, again, Umar is using the full shells explanatory principle as the basis for explaining the bond in terms of electrons 'filling up the gaps' in the electron shells, rather than considering how electrical interactions can hold the structure together. Umar's suggestion that the sharing of electrons "fills up the – last electron needed in one of the chlorine shells" demonstrates the anthropomorphic language (e.g., what an atom wants or needs) commonly used when learners have acquired aspects of the common octet rule framework that is developed from the full shells explanatory principle and used by many learners to explain bonding reactions, chemical reactions, patterns in ionisation energy, and chemical stability.

Responding to a misconception about my own teaching

Keith S. Taber

There are many postings here about things that learners said, and so presumably thought, about curriculum topics that would likely surprise, if not shock, the teachers who had taught them those topics. I am certainly not immune from being misunderstood. Today, I reflect on how someone seems to have understood some of my own teaching, and indeed seriously objected to it.

When I have called-out academic malpractice in this blog the targets have usually been conference organisers or journal administrators using misleading (or downright dishonest) techniques, or publishers mistreating authors. I feel somewhat uneasy about publicly contradicting a junior scholar. However, I also do not appreciate being publicly described as deliberately misleading a student, as has happened here, and my direct challenge to the blog author was rejected.

The accusation

A while back some Faculty colleagues referred me to a blog that included the following comments:

In the Faculty of Education students pursuing the MPhil or PhD take a research ethics lecture that presents the Tuskegee Syphilis Study as ethically sound, but only up to the year 1947 when penicillin was actively being used to treat syphilis. According to the Cambridge lecturer, that's the point when the study became unethical.

When I interrupted his lecture to object to his presentation, I was told by that lecturer that he'd never received any objections in his many, many years of teaching the same slides on the same course. That was not true. He knew and the Faculty knows and yet that false information continues to be disseminated to students, many of whom will go on to complete research in developing countries where their only reference for their ethical or unethical behavior is this lecture.

I am not named, but virtually anyone in my Faculty, or having taken graduate studies there in the last few years, would surely know who was being discussed. As is pointed out in our Educational Research course, and the Research Methods strand of other graduate courses, if you want to avoid someone being identified in your writing, it is not enough to not name them. I can be fairly confident the author of the comments above should have known that: it is a point made in the very lecture being criticised.

This blog posting seems to have received quite a lot of attention among students at the University Faculty where I worked. Yet the two claims here are simply not correct. The teaching is seriously misrepresented, and I certainly did not lie to this student.

The blog invited me to 'Leave a Reply', so I did. My comments were subject to moderation – and the next morning I found a response in my email in-box. My comments would not be posted, and the claims would not be amended: I was welcome to post my reply elsewhere, but not at the site where I was being criticised. So, here goes:

The (rejected) reply

I hope you are well.

I was directed to your blog by a group of scholars in the Faculty (Of Education at Cambridge). It is an impressive blog. However, I was rather surprised by some of what you have posted. I was the lecturer you refer to in your posting who taught the lecture on research ethics. I do indeed remember you interrupting me when I was presenting the Tuskagee syphilis study as an example of unethical research. I always encouraged students to participate in class, and would have welcomed your input at the end of my treatment of that example.

However, having read your comments here, I do need to challenge your account. I do not consider that the Tuskegee syphilis study was initially ethically sound, and I do not (and did not) teach that. I certainly did make the point that even if the study had been ethical until antibiotics were widely available, continuing it beyond that point would have been completely unjustifiable. But that was certainly not the only reason the study was unethical. Perhaps this would have been clearer if you had let me finish my own comments before interjecting – but even so I really do not understand how you could have interpreted the teaching that way.

Scheme (an annotated version of 'the ethical field', Taber, 2013a, Figure 9.1) used to summarise ethical issues in the Tuskegee syphilis study in my Educational Research lecture on ethical considerations of research.

The reference to 1947 in the posting quoted above relates to the 'continue' issue under research quality – the research (which involved medical staff periodically observing, but not treating, diseased {black, poor, mostly illiterate} men who had not been told of the true nature of their condition) was continued even when effective, safe treatment was available and any claims to the information being collected having potential to inform medical practice became completely untenable.

I may well have commented that no one had ever raised any objections to the presentation when I had given the lecture on previous occasions over a number of years – because that is true. No one had previously raised any concerns with me regarding my teaching of this example (or any aspect of the lecture as far as I can recall). I am not sure why you seem to so confidently assume otherwise: regarding this, you are simply wrong.

Usually in that lecture I would present a brief account of the Milgram 'learning' experiment, which would often lead to extended discussion about the ethical problems of that research in relation to its motivation and what was usefully learnt from it. Then, later in the session, I would talk about the Tuskegee study, which normally passed without comment. I had always assumed that was because the study is so obviously and seriously problematic that no one would see any reason to disagree with my critique. Then I would go on to discuss other issues and studies. I can assure you that no one had previously, before you, raised any concerns about my teaching of this example with me. If anyone in earlier cohorts had any concerns about this example they would have been welcome to talk to me about them – either in class, or privately afterwards. No one ever did.

I have no reason to believe that colleagues at Cambridge are deliberately disseminating false information to students, but then I do not audit other teaching officers' lectures, and I cannot speak for them. However, I can speak for myself, just as you rightly speak up for yourself. I have certainly always taken care to do my best not to teach things that are not the case. Of course, as a school and college science teacher I was often teaching models and simplifications, and not the 'whole' truth, but that is the nature of pedagogy, and is something we should make clear to learners (i.e., that they are being taught models and simplifications that can later in their studies be developed through more sophisticated treatments).

In a similar way, I used simplifications and models in my research methods lectures at Cambridge – for example, in terms of the 'shape' of a research project, or contrasting paradigms, or types of qualitative analysis, and so on, but would make explicit to the class that this is what they were: 'teaching models'. I entered the teaching profession to make a positive difference; to help learners develop, and to acquire new understandings and perspectives and skills; not to misinform people. I very much suspect that on occasions I must have got some things wrong, but, if so, such errors would always have been honest mistakes. I have never knowingly taught something that I thought was untrue.

So, whilst I admire your courage in standing up for what you believe, and I certainly wish you well, what you have written is not correct, and I trust my response will be posted so that your inaccurate remarks will not go unchallenged. I suspect that you are not being deliberately untruthful (you accuse me of telling you something I knew was not true: I try to be charitable and give people the benefit of doubt, so I would like to think that you were writing your comments in good faith), but I do not understand how you managed to come to the interpretation of my teaching that you did, and wish that you would have at least heard me out before interrupting the class, as that may have clarified my position for you. The Tuskegee syphilis study was a racist, unethical study that misled and abused some of those people with the lowest levels of economic and political power in society: people (not just the men subjected to the study, but also their families) who were betrayed by those employed by the public health service that they trusted (and should have been able to trust) to look after their interests. I do not see how anyone could consider it an ethically sound study, and I struggle to see why you would think anyone could.

Your claim that I lied about not having previously received complaints about my teaching of this topic before is simply untrue – it is a falsehood that I hope you will be prepared to correct.

What should a 'constructivist' teacher make of this?

I should be careful about criticising a student for thinking I was teaching something quite different from what I thought I was teaching. I have spent much of my career telling other teachers that learners will make sense of our teaching in terms of the interpretive resources they have available, and so they may interpret our teaching in unexpected ways. Learners will always be biased to understand in terms of their expectations and past experiences. We see it all the time in science teaching, as many of the posts here demonstrate.

I have described learning as being an incremental, interpretive, and so iterative, process and not a simple transfer of understanding (Taber, 2014). Teaching (indeed communication) is always a representation of thinking in a publicly accessible form (speech, gesture, text, diagrams {what sense does the figure above make out of the context of the lecture?}, models, etc.) – and whatever meaning may have informed the production of the representation, the representation itself does not have or contain meaning: the person accessing that presentation has to impose their own interpretation to form a meaning (Taber, 2013b). After teaching and writing about these ideas, I would be a hypocrite to claim that a learner could not misinterpret my own teaching as I can communicate perfectly to a room full of students from all around the world with different life experiences and varied disciplinary backgrounds!

Even so, I am still struggling to understand the interpretation put on my teaching in this case, despite going back to revisit the teaching materials a number of times. Most of the points I was making must have been completed disregarded to think I did not consider the study, which ran from 1932 to 1972 (Jones, 1993) unethical until 1947. So, even for someone who claims to be a constructivist teacher and knows there is always a risk of learners misconceiving teaching, this example seems an extreme case.

The confident claim that it was not true that I had not received previous complaints about my teaching of this example is even harder to understand. It is at least a good reminder for me not to assume I know what students are thinking or that they know what I am thinking, or can readily access the intended meaning in my teaching. I've made those points to others enough times, so I will try to see this incident as a useful reminder to follow my own advice.

Sources cited:

The cell nucleus is probably bigger than an atomic nucleus

A cell is about ten times larger than an atom

Keith S. Taber

Dividing cell image by  ar130405 from Pixabay

Bert was a participant in the Understanding Science Project. Bert was interviewed in Y10 and asked about the topics he had been studying, which included circulation in biology, static electricity in physics, and oxidation in chemistry.

He talked about protons, electrons and atoms in both chemistry and physics, and was asked if this could also link with biology. Bert suggested that the nucleus comes up in chemistry (in the context of atomic structure) and physics (in the context of static electricity), and in biology in the context of cells (see 'The nucleus is the brain of the cell'). From the perspective of the science teacher, there is little basis for confusing the nucleus of an atom with that of a cell: obviously a cell is a complex entity with many components, each of which has itself a complex supra-molecular structure – so clearly the atomic nucleus is on a scale many orders of magnitude smaller than a cell nucleus.

However, the expert perspective is based on relating a lot of knowledge that the novice may not yet have, or at least, may not yet be coordinating. In Bert's case, he was only just starting to coordinate these ideas, as became clear when Bert was asked about the relative sizes of atomic and cell nuclei:

Which do you think is bigger, an atom or a cell, or are they both about the same size?

I'd say a cell.

A correct, but hardly confident and definitive, response. I followed up:

Which do you think is bigger, an atom or a cell, or are they both about the same size?

I'd say a cell.

So which do you think is bigger, the nucleus of a cell or the nucleus of an atom, or do you think they're both about the same size?

I think they're both about, well I should, oh. (Laughs) I'd say the one in the cell is probably bigger.

Why do you think that?

Well it's a cell, I'd have thought it was bigger than the atom. And you know, if the nucleus is kind of the main part of it, then it would probably be about, it would be the • same sort of – If the atom was brought to the size of the cell then the nucleus would be the same size I would have thought. So if the atom is smaller then the nucleus is a lot smaller.

I see, so you are sort of like scaling it, accordingly?

Yeah.

I see. So any idea roughly, just very roughly, how much bigger a cell is than an atom?

Erm oh, it's, they're both really microscopic so, I couldn't really say how much bigger they are than each other.

So it seems that Bert would "have thought [the cell] was bigger than the atom", but he did not seem entirely certain of this, whereas from the scientific perspective the difference in scale is considered vast and highly significant. Although cells are generally microscopic entries, they are more like familiar macroscopic objects that we can handle in everyday life than quanticles such as atoms which do not behave like familiar objects. (So, there is sense in which it is meaningless to talk about the size of atoms as they have no edges or surfaces but rather fade away to infinity.)

Erm oh, it's, they're both really microscopic so, I couldn't really say how much bigger they are than each other.

Mm. No, okay. So if I said a cell was ten times bigger than an atom, a hundred times bigger than an atom, a thousand times bigger than an atom?

I wouldn't say that, I'd say, I'd probably go with the first one you said, ten times bigger.

So roughly ten times bigger than an atom. So a nucleus of a cell you'd expect to be roughly ten times bigger than the nucleus of an atom?

Yeah.

But you're not really sure?

Well no, there are a lot more parts in a cell than there is in an atom. So I'd say the nucleus is… if they're both brought to the same size again, I'd say the nucleus of the atom would be bigger than the cell. But I could be totally wrong.

Oh I see, so you've got two arguments there. That because they, because they both have a nucleus in the middle, that in terms of scale, if the cell is quite a bit bigger than the atom, you'd expect the nucleus of the cell would be quite a bit bigger than the atom. But an atom is quite a simple structure, whereas a cell has a lot more things in it, it's a lot more complex.

Yeah.

So maybe there's not so much room for the nucleus of the cell as there is for an atom because you've got to fit so much more in.

Yeah.

Is that what you're thinking?

Yeah.

Bert's thinking here is quite reasonable, within the limits of his knowledge. He suggests that a cell nucleus will be larger than an atomic nucleus, because a cell is larger than an atom. However, he only think the cell nucleus will be about ten times the size of the atomic nucleus as he suspects the cell is only about ten times the size of an atom – after all they are both "really microscopic".

However, he also points out that a cell seems to have a more a lot more components to be fitted in, which would suggest that perhaps there is less space to fit the nucleus, so perhaps it would not be as much as ten times bigger than the atomic nucleus.

So Bert is able to consider a situation where there may be several factors at work (the size of the cell versus the size of the atom; the multitude of cellular components versus the sparsity of atoms) and appreciate how they would operate in an opposite sense within his argument so one could compensate for the other. (This type of thinking is needed a lot in studying science. One example is comparisons of ionisation enthalpies between different atoms and ions. I also recall physics objective examination questions that asked students to compare, say, the conductance of two wires with different resistivity, length and area.)

It is not reasonable to expect Bert to know just how much larger a typical cell nucleus is to an atomic nucleus, however, it is likely the science teacher would expect Bert to be aware that the nucleus is one small part of the atom, which is a constituent of the molecules and ions that are the chemical basis for the organelles such as nuclei found in cells. Bert had told me "there are lots of atoms in you", but he did not seem to have understood the role those atoms played in the structure of all tissues. This would seem to be an example of a fragmentation learning impediment, where a learner has not made the connections between topics and ideas that a science teacher would have intended and expected.

Some stars are closer than the planets

Stars look so little because they are a long way away, but some stars are closer than the planets

Keith S. Taber

Sophia was a participant in the Understanding Science Project. When I interviewed her in her first year of secondary school (Y7 in the English school system). I asked her about what she remembered about the science she had studied in primary school. She told me about she had studied the topic of space, and had learnt about the nine planets. When I asked her if she could name the planets she produced a list of planets including both the moon and sun: "Pluto, Jupiter, Venus, Uranus, Earth, the Sun, the Moon".

[Read 'The sun is the closest of the eleven planets']

As Sophia thought the sun might be a planet, I asked her what a planet was:

Do you know what a planet is?

Erm, it's like – a round – a sphere, in space, kind of. Though we don't know if people live, animals live there or not.

…If I say someone was going through space, in a spaceship, and they are a long, long way away from earth, they've gone a long way across space, and they came across something in space…And er one of the crew said 'oh that's a planet'. And another one of the crew said 'no, that's not a planet'. And you were in charge, you were the captain. How would you decide who was right, whether that was a planet or not in space?

Er

(pause, c.5s)

I'd look if it was all the things that you thought a planet was.

Good, and what would that be?

If it was round, if it was a bit lumpy, a bit – if it was quite big, not like a little star, well there's no stars that little…

It seemed that Sophia (reasonably) thought stars would be larger than planets, which invited an obvious question, that I assumed would have an almost-as-obvious answer.

Why do they [the stars] look so little?

Because they are a long way away.

Oh, I see. So they are big really?

Yeah.

Okay. What's the difference between a star and a planet then?

A star's made up of different things, but planets – can't – cause you don't really see a planet, so you just see stars quite lot.

That's true, there is lots and lots of stars up there, isn't there? So how can you see the stars and not the planets, do you think?

I think the stars, some stars are closer, maybe, than planets.

There seemed to be something of a contradiction here. Sophia thought that 

  • stars were not as 'little' as planets
  • but they seemed little because they were a long way away.
  • but the stars were easier to see than planets
  • so they might be closer to us than the planets.

Both these arguments are logical enough suggestions (things seem smaller, and may be harder to see, if they are a long way off), but there was a lack of integration of ideas as her two explanations relied on seemingly inconsistent premises (that the stars are "are a long way away" but could be "closer, maybe, than planets").

It seemed that Sophia was not aware, or was not bringing to mind, that stars were self-luminous whereas planets were only seen by reflected light. Lacking (or not considering) that particular piece of information acted as a 'deficiency learning impediment' and led to her explaining why the planets could be more difficult to see by suggesting they might not be as close as some stars.

Not considering luminosity as a criterion also seemed to explain why she was not clear that the (self-luminous) sun was not a planet.

[Read 'The sun is the closest of the eleven planets']

The sun is the closest of the eleven planets

Keith S. Taber

Sophia was a participant in the Understanding Science Project. When I interviewed her in her first year of secondary school (Y7 in the English school system). I asked her about what she remembered about the science she had studied in primary school. She told me about she had studied the topic of space.

So what did you learn about space?

All the planets, and – 

(pause, c.2 s)

So how many planets are there?

Nine.

Nine, okay. Do you know them all?

No (laughs)

Do you know some of them?

Erm. Pluto, Jupiter, Venus, Uranus, Earth, the Sun, the Moon – (pause, c.2s) hm.

[This was a few years back, and I think was before Pluto was demoted from full planet status in the scientific community.] So, Sophia seemed to have an alternative conception of what would be considered a planet, and she was counting both the moon and the sun among the planets. After a little further conversation about other candidates we came up with a list of more than nine planets.

So how many does that make?

(Sophia laughs)

(Pause, c.6s)

Is there eleven?

Well you said there was nine, didn't you?

Yeah. (laughing)

How could that be, how could we get these extra two?

(Pause, c.4s)

… So, Mercury, is that a planet?

Hm.

Okay, Venus?

Yep.

Earth?

Uh hm.

Mars?

Yeah.

The Moon?

Hm, yeah.

Yeah, Jupiter?

(Pause, 2.s)

Saturn?

(Pause, 2.s)

The Sun?

I'm not sure about the Sun.

Not sure about the Sun.

I think so.

Neptune?

Uranus?

Yep.

Pluto?

Uh hm.

So Sophia was not entirely sure the sun should be considered as planet, although she seemed more confident about the moon. The earth and moon are not technically considered as a double planet system, even though the moon is unusually large satellite compared the the planet it orbits, as the system's centre of mass is within the earth. (Strictly, the earth, as well as the moon, orbits their joint centre of mass.)

As Sophia thought the sun might be a planet, I asked her what a planet was, and the difference between planets and stars. She suggested that some stars are closer to us than the planets.

[Read 'Some stars are closer than the planets']

Not considering luminosity to be a factor, Sophia did not consider the sun to be a star:

What's the closest planet to you?

Erm – the Sun?

Yeah?

If it is a planet.

I think that might there might have been a trick question there. Which is the closest planet to you?

To me?

Yeah.

Earth.

Is mass conserved when water gets soaked up?

Setting up a thought experiment on plant growth and mass

Keith S. Taber

Image by truthseeker08 from Pixabay 

Sophia was a participant in the Understanding Science Project.

I was aware that research has suggested that children often do not appreciate how carbon obtained from the carbon dioxide in the air is a key source of matter for plants to build up tissue, so learners may assume that the mass increase during growth of a plant will be balanced by a mass reduction in the soil it is growing in.

"The extra [mass of a growing tree] comes from the things it eats and drinks from the ground. It's just like us eating and getting larger."

Response of 15 year old student in the National science survey carried out the Assessment of Performance Unit of the Department of Education and Science, as reported in Bell and Brook, 1984: 12.

During an interview in her first year of secondary education (Y7), Sophia reported that she had been studying plants in science, and that generally a plant was "a living thing, that takes up things from soil, to help it grow" (although some grew in ponds). Sophia was therefore asked a hypothetical question about weighing a pot of soil in which a seed was planted, with the intention of seeing if she thought that the gain in mas of the seed as it grew into a mature plant would be balanced by a loss of mass from the soil.

Sophia was asked about a pot of soil (mass 400g) in which was planted a seed (1g), and which was then watered (adding 49g of water).

The scenario outlined to Sophia

There seemed two likely outcomes of this thought experiment:

  • A learner considers that the mass of pot, seed and water is collectively 450g, and assumes that as the mass of plant grows, the mass of soil decreases accordingly to conserve total mass at 450g.
  • A learner is aware that in photosynthesis carbon is 'captured' from carbon dioxide in the air, so the mass of the plant in the soil will exceed 450g once the plant grows.

Of course, a learner might also invoke other considerations – the evaporation of the water, or the acquisition of water due to condensation of water from cold air (e.g., dew); that soil is not inert, but contains micro-organisms that have their own metabolism, etc.

I first wanted to check that Sophia appreciated we had (400 + 1 + 49 =) 450g of material at the point the seed was first watered. That was indeed her initial thought, but she soon 'corrected' herself.

Any idea how much it would weigh now?

[Four] hundred and fifty, no, cause, no cause it will soak it up, wouldn't it, so just over four hundred (400).

So we had four hundred (400) grammes of soil plus pot, didn't we?

Uh hm.

…And we had one (1) gramme of erm, of plant seed. Just one little seed, one (1) gramme. And forty nine (49) grammes of water. But the water gets soaked up into the soil, does it? So when it's soaked up, you reckon it would be, what?

Erm, four hundred and twenty (420).

Sophia's best guess at the mass of the pot with soil (initially 400g) after planting a 1g seed and adding 49g of water was 420g, as the water gets soaked up.

So, Sophia suggests that although 49g of water has been added to a pot (with existing contents) of mass 401g , the new total mass will be less than 450g, as the water is soaking into the soil. Her logic seems to be that some of the water will have soaked into the soil, so it's mass is not registered by the balance.

If you poured the water in, quite quickly, not so quickly that it splashes everywhere, but quite quickly. Before it had a chance to soak up, if you could read what it said on the balance before it had a chance to soak up, do you think it would say four hundred and twenty (420) grammes straight away?

No, it would probably be just under, erm, four hundred and fifty (450).

And it would gradually drop down to about four twenty (420) say, would it?

Yeah.

Might be four hundred and fifteen? (415) Could be four hundred and twenty five (425)?

Yeah.

Not entirely sure,

No

but something like that?

Yeah.

It appears Sophia recognises that in principle there would be a potential mass of 450g when the water is added, but as it soaks up, less mass is registered.

Sophia recognises that mass is initially conserved, at least before the water soaks into the soil.

In other words Sophia in the context of water soaking into soil is not conserving mass.

This is a similar thought experiment to when students are asked about the mass registered during dissolving, where some learners suggest that as a solid dissolves the total mass of the beaker/flask plus its contents decreases, as if the mass of the dissolved material is not registered (Taber, 2002). In that case it has been mooted that ideas about buoyancy may be involved – at least when it is clear that the learners recognise the dissolved material is still present in the solution.

However, that would not explain why Sophia thinks the balance would not register the mass of water soaked into the soil in this case. Rather, it sees more a notion that 'out of sight' is out of mass. Sophia's understanding of what is happening to mass here would be considered an alternative conception or misconception, and is likely based on her intuition about the scenario (acting as a grounded learning impediment) rather than something she has been told.

Sources cited:

Sleep can give us energy

Sleep, like food, can give us a bit more energy

Keith S. Taber

Image by Daniela Dimitrova from Pixabay 

Jim was a participant in the Understanding Science Project. When I was talking to students on that project I would ask them what they were studying in science, rather than ask them about my own agenda of topics. However, I was interested in the extent to which they integrated and linked their science knowledge, so I would from time to time ask if topics they told me about were linked with other topics they had discussed with me. The following extract is taken from the fourth of a sequence of interviews during Jim's first year in secondary school (Y7 in the English school system).

And earlier in the year, you were doing about dissolving sugar. Do you remember that?

Erm, yeah.

Do you think that's got anything to do with the human body?

Erm, we eat sugar.

Mm. True.

Gives us energy…It powers us.

Ah. And why do we need power do you think?

So we can move.

This seemed a reasonable response, but I was intrigued to know if Jim was yet aware of metabolism and how the tissues require a supply of sugar even when there is no obvious activity.

Ah what if you were a lazy person, say you were a very lazy rich person? And you were able to lie in bed all day, watch telly, whatever you like, didn't have to move, didn't have to budge an eyelid, … you're rich, your servants do everything for you? Would you till need energy?

Yes.

Why?

I dunno, 'cause being in bed's tired, tiring.

Is it?

When I'm ill, I stay off for a day, I just feel tired, and like at the end of the day, even more tired than I do when I come to school some times.

Jim's argument failed to allow for the difference in initial conditions

Staying in bed all day and avoiding exercise could indeed make one feel tired, but there seemed something of a confound here (being ill) and I wondered if the reason he stayed in bed on these days might be a factor in feeling even more tired than usual.

So maybe when you are ill, you should come to school, and then you would feel better?

No.

No, it doesn't work like that?

No.

Okay, so why do you think we get tired, when we are just lying, doing absolutely nothing?

Because, it's using a lot of our energy, doing something.

Hm, so even when we are lying at home ill, not doing anything, somehow we are using energy doing something, are we?

Yes.

What might that be, what might we use energy for?

Thinking.

I thought this was a good response, as I was not sure all students of his age would realise that thinking involved energy – although my own conceptualisation was in terms of cellular metabolism, and how thinking depend on transmitting electrical signals along axons and across synapses. I suspected Jim might not have been thinking in such terms.

Do you think it uses energy to think?

(Pause, c.3s)

Probably.

Why do you think that?

Well cause, like, when you haven't got any energy, you can't think, like the same as TV, when it hasn't got any energy, it can't work. So it's a bit like our brains, when we have not got enough energy we feel really tired, and we just want to go to sleep, which can give us more energy, a bit like food.

So Jim here offered an argument about cause and effect- when you haven't got any energy, you can't think. This would certainly be literally true (without any source of energy, no biological functioning would continue, including thinking) although of course Jim had clearly never experienced that absolute situation (as he was still alive to be interviewed), and was presumably referring to experiences of feeling mentally tired and not being able to concentrate.

He offered an analogy, that we are like televisions, in that we do not work without energy. The TV needs to be connected to an electrical supply, and the body needs food (such as sugar, as Jim had suggested) and oxygen. But Jim also used a simile – that sleep was like food. Sleep, like food, according to Jim could give us energy.

So sleeping can give us energy?

Yeah.

How does that work?

Er, it's like putting a battery onto charge, probably, you go to sleep, and then you don't have to do anything, for a little while, and you, then you wake up and you feel – less tired.

Okay so, you think you might need energy to think, because if you have not got any energy, you are very tired, you can't think very well, but somehow if you have a sleep, that might somehow bring the energy back?

Yeah.

So where does that energy come from?

(Pause c.2s)

Erm – dunno.

So here Jim used another analogy, sleeping was like charging a battery. When putting a battery on change, we connect it to a charger, but Jim did not suggest how sleep recharged us, except in that we could rest. When sleeping "you don't have to do anything, for a little while", which might explain a pause in depletion of energy supplies, but would not explain how energy levels were built up again.

[A potentially useful comparison here might have been a television, or a lap top used to watch programmes, with an internal battery, where the there is a buffer between the external supply, and the immediate source for functioning.]

This was an interesting response. At one level it was a deficient answer, as energy is conserved, and Jim's suggestion seemed to require energy to be created or to appear from some unspecified source.

Jim's responses here offered a number of interesting comparisons:

  • sleep is a bit like food in providing energy
  • not having energy and not being able to think is like a TV which cannot work without energy
  • sleeping is like putting a battery on charge

Both science, and science teaching/communication draw a good deal on similes, metaphors and analogies, but they tend to function as interim tools (sources of creative ideas that scientists can then further explore; or means to help someone get a {metaphorical!} foothold on an idea that needs to later be more formally understood).

The idea that sleeping works like recharging a battery could act as an associative learning impediment as there is a flaw in the analogy: putting a battery on charge connects it to an external power source; sleep is incredibility important for various (energy requiring) processes that maintain physical and mental health, and helps us feel rested, but does not in itself source energy. Someone who thought that sleeping works like recharging a battery will not need to wonder how the body accesses energy during sleep as they they seem to have an explanation. (They have access to a pseudo-explanation: sleep restores our energy levels because it is like recharging a battery.)

Jim's discourse reflects what has been called 'the natural attitude' or the 'lifeworld', the way we understand common experiences and talk about them in everyday life. It is common folk knowledge that resting gives you energy (indeed, both exercise and rest are commonly said to give people energy!)

In 'the lifeworld', we run out of energy, we recharge our batteries by resting, and sleep gives us energy. Probably even many science teachers use such expressions when off duty. Each of these notions is strictly incorrect from the scientific perspective. A belief that sleep gives you energy would be an alternative conception, and one that could act as a grounded learning impediment, getting in the way of learning the scientific account.

Yet they each also offer a potential entry point to understanding the scientific accounts. In one respect, Jim has useful 'resources' that can be built on to learn about metabolism, as long as the habitual use of technically incorrect, but common everyday, ways of talking do not act as learning impediments by making it difficult to appreciate how the science teacher is using similar language to express a somewhat different set of ideas.

Sodium and chlorine don't actually overlap or anything

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 of the English school system). Annie was shown, and asked about, a sequence of images representing atoms, molecules and other sub-microscopic structures of the kinds commonly used in chemistry teaching. She was shown a representation of part of a lattice in sodium chloride.

Focal figure (Fig. 5) presented to Annie

Any idea what that's meant to be?

(pause, c.6s)

Just sodium and chlorine atoms

That's sodium and chlorine atoms, erm would you say that there was any kind of bonding there?

No.

Although the image included the standard '+' and '-' symbols to signify that ions were shown, Annie referred to "atoms". It transpired that Annie had an idiosyncratic understanding of what was meant by charge. (Read: Na+ has an extra electron in its outer shell and Cl- is minus an electron and K-plus represents a potassium atom that has an extra electron.)

Annie had already identified chemical bonding in representations of molecules of hydrogen , tetrachloromethane , and oxygen, so she was asked why she though there was no bonding in this example:

No bonding. Why do you say that? What is the difference between that and the ones we've seen before?

Well the other ones electrons were shown, and these no electrons are shown and they don't actually overlap or anything they just go in rows.

They go in rows. Okay. … but unlike (the images) we've seen previously they've had bonds in,

Yeah.

chemical bonds, whereas this, we don't have chemical bonds?

No.

So Annie did not interpret the representation of NaCl as portraying bonding. However, on further probing she did recognise that the structure could get held together by forces.

When Annie was asked if what was shown in the figure would would fall apart or hold together, Annie suggested that If you heated it, or reacted it in some way, it would hold together, and it would probably get held together by just forces. However, she did not consider that (i.e., even after reacting) amounted to chemical bonding. (Read: Sodium has one extra electron in its outer shell, and chlorine is minus an electron, so by force pulls they would hold together.)

The canonical interpretation of the figure is that it is a slice through a three dimensions structure of ions, where the attractive forces between cations pull the ions into a bound structure (to the point where attraction and repulsions are in equilibrium), and that this kind of binding is called ionic bonding.

Annie did not see ions, but atoms. She thought there was no bonding because no overlap was shown. In chemistry a wide range of different types of representation are used to show structures at the submicroscopic level – bonds may sometimes be shown by lines or sometimes by overlap or (in the case of ionic structures) neither. This is a potential source of confusion for learners who may not appreciate why different conventions may be used to represent different, or even the same, structures.

Some particles are softer than others

Keith S. Taber

Image by Alexander Ignatov from Pixabay

Bill was a participant in the Understanding Science Project. Bill was a Year 7 student when he told me that previously, when he had been in primary school, "we did a lot about plants, and – inside them, how they produce their own food". As he had been talking to me about learning about particles (e.g. Gas particles try to spread out and move apart), I asked if there was any link between these two topics.

Okay. What about particles, we were just talking about particles, do you think that's got anything to do with particles?

Well in the plant, there is particles.

Are there?

'cause it's a solid.

Ah. So there'll be particles in that then?

Yeah.

Is it all solid, do you think?

Inside the stem is, 'cause going up the stem there would be water, so that's a liquid. And, it also uses oxygen, which is a gas, to make its food, so. I think so.

So it would be solids, liquids and gases?

Mm, I think some.

But they've all got some particle in them, they are all made up of particles.

Yeah.

Okay.

As Bill had talked to me earlier about there being particles in a gas when ice was melted, and then boiled, I wanted to see if he though the particles in different substances were the same:

Erm. Do you think that the particles in the – oxygen's a gas isn't it?

Yeah.

Do you think the particles in the oxygen gas, are the same as the particles in the steam that you said was a gas, in your experiment you did earlier?

Erm, I don't think so, no.

You think they'd be different sort of particles?

Yeah, they're different gases.

Okay. And in the solid part of the plant, do you think the particles that make up the solid part of the plant, are the same as the particles that make up this table, that's a solid?

Well, the particles, plants are soft, some plants are soft, and you, when you squeeze them they're, they feel soft and erm, but the table is hard so I think that the particles would be slightly different, but they would have, because they hold this different shape, and they would, they would be {pause} erm {pause} then they would, ob¬, then they would be softer as well.

So the softer, the plant which is softer, > > would have softer particles?

< Yeah. < I think so yeah

And the harder wood, made of harder particles?

I think so.

Here Bill offered evidence of a very common alternative conception about the particle theory. A key feature of particle theory is that chemists use particle models to explain the properties of substances macroscopically (what can be observed directly) in terms of the very different nature and properties of conjectured 'particles' (quanticles) at a submicroscopic level.

Yet after learning about these 'particles', students commonly 'explain' macroscopic properties of substances and materials by suggesting that the particles of which they are made up themselves have the property to be explained – being hard, sharp, colourless, conducting, etc.

Single bonds are different to covalent bonds

Single bonds are different to covalent bonds or ionic bonds

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 of the English school system). Annie was shown, and asked about, a sequence of images representing atoms, molecules and other sub-microscopic structures of the kinds commonl y used in chemistry teaching. She was shown a representation of the resonance between three canonical forms of BF3, sometimes used as away of reflection polar bonding. She had just seen another image representing resonance in the ethanoate ion, and had suggested that it contained a double bond. She had earlier in the interview referred to covalent bonding and ionic bonding, and after introducing the ideas of double bond, suggested that a double bond is different to a covalent bond.

Focal figure (14) presented to Annie

What about diagram 14?…

Oh.

(pause, c.13s)

Seems to be different arrangements. Of the three, or two elements.

Uh hm.

(pause, c.3s)

Which are joined by single bonds.

What, where, what single, what sorry are joined by single bonds?

All the F to the B to the F. Are single bonds they are not double like before. [i.e., a figure discussed earlier in the interview]

So are they covalent bonds? Or ionic bonds, or? Or are single bonds something different again?

Single bonds are different.

This reflected her earlier comment to the effect that a double bond is different to a covalent bond, suggesting that she did not appreciate how covalent bonds are considered to be singular or multiple.

However, as I checked what she was telling me, Annie's account seemed to shift.

They're different to double bonds?

Yeah.

And are they different to covalent bonds?

No 'cause you probably get covalent bonds which are single bonds.

So single bonds, just moments before said to different to covalent bonds, were now 'probably' capable of being covalent. As she continued to answer questions, Annie decided these were 'probably' just alternative terms.

So covalent bonds and single bonds, is that another word for the same thing?

Yeah, probably. But they can probably occur in different, things like in organic you talk about single bonds more than you talk about covalent, and then like in inorganic you talk about covalent bond, more than you talk about single bonding or double bonding.

So you think that maybe inorganic things, like sort of, >> copper iodide or something like that, that would tend to be more concerned with covalent bonds?

< Yeah. < Yeah.

But if you were doing organic things like, I don't know, erm, ethane, >> that's more likely to have single bonds in.

< Yeah. < Yeah.

So single bonds are more likely to occur in carbon compounds.

Yeah.

And covalent bonds are more likely to occur in some other type of compound?

Yeah. Sort of you've got different terminology, like you could probably use single bonds to refer to something in inorganic, but when you are talking about the structures and that, it's easier to talk about single bonds and double bonds, rather than saying that's got a covalent bond or that's got an ionic bond.

Annie's explanation did not seem to be a fully thought-out position. It was not consistent with the way she had earlier reported there being five covalent bonds and one double bond in an ethanoate ion.

It seems likely that in the context of the research interview, where being asked directly about these points, Annie was forced to make explicit the reasons she tended to label particular bonds in specific ways. The interview questions may have acted like Socratic questioning, a kind of scaffolding, leading to new insights. Only in this context did she realise that the single and double bonds her organic chemistry lecturer talked about might actually be referring to the same entities as the covalent bonds her inorganic chemistry lecturer talked about.

It would probably not have occurred to Annie's lecturers (of which, I was one) that she would not realise that single and double bonds were covalent bonds. It may well have been that if she had been taught by the same lecturer in both areas, the tendency to refer to single and multiple bonds in organic compounds (where most bonds were primarily covalent) and to focus on the covalent-ionic dissension in inorganic compounds (where degree of polarity in bonds was a main theme of teaching) would still have lead to the same confusion. Later in the interview, Annie commented that:

if I use ionic or covalent I'm talking about, sort of like a general, bond, but if I use double or single bonds, that's mainly organic, because sort of it represents, sort of the sharing, 'cause like you draw all the molecules out more.

This might be considered an example of fragmentation learning impediment, where a student does not make a link that the teacher is likely to assume is obvious.

Plants mainly respire at night

Plants mainly respire at night because they are photosynthesising during the day

Keith S. Taber

Image by Konevi from Pixabay 

Mandy was a participant in the Understanding Science Project. When I spoke to her in Y10 (i.e. when she was c.14 year old) she told me that photosynthesis was one of the topics she was studying in science. So I asked her about photosynthesis. She suggested that "respiration produces energy, but photosynthesis produces glucose which produces energy". (See 'How plants get their food to grow and make energy'). She told me that she respired to get energy.

How do you get your energy then?

We respire.

Is that different then [from photosynthesis]?

Yeah.

So what's respire then, what do you do when you respire?

We use oxygen to, and glucose to release energy.

Do plants respire?

Yes.

So when do you respire, when you are going to go for a run or something, is that when you respire, when you need the energy?

No, you are respiring all the time.

… What about plants? Do they respire all the time?

They mainly do it at night.

Why's that?

'cause they're photosynthesising during the day, cause they need the light.

I was not clear why Mandy thought that plants should respire less when they were photosynthesising.

So why do you need to respire all the time?

'cause you're making energy and you need energy to do everything.

So are you respiring at the same rate all the time, do you think?

No.

So sometimes more than others?

Yeah.

So when might you need to respire more?

When you are doing exercise. Running around a lot.

So are there time when you do not need to respire as much?

Yeah.

So when might you not need to respire very much?

When you 're sleeping or just sitting watching tele [television].

…Do you have to respire at all during the night – you are not doing anything are you?

You need a little bit of energy.

What for?

Erm, I don't [indistinct], well I suppose it's just to keep everything, cause if you did not have energy then your heart would not beat, and you need it to keep breathing, and your heart pumping.

Mandy recognised the need for people to respire continuously, although she associated this with functioning at the organism level (breathing, blood circulation) and did not seem to be thinking about cellular level metabolism.

Why do plants need to respire? What do they use it, the energy for?

Erm, to grow, and to fix cells that are – broken.

Oh right, like repair damage?

Yeah.

So, do you think they are like us then, that they sort of sleep sometimes and don't need to respire as much, or?

Not as much, I don't know. I don't know.

Do you think a plant sleeps, a tree has a good sleep?

No.

So when do you think plants need to respire the most, or do you think they respire the same all the time?

They respire more at night, because – they do it then instead of in the day because they do photosynthesis during the day, but they still respire a little bit.

So is it difficult to try and do both at the same time?

Probably.

Or just maybe they are too busy photosynthesising to do much respiration?

Yeah, erm, I don't know.

Not sure?

No.

Mandy was not offering any specific reason why a plant should need to respire less at night (and did not seem to have previously thought about this), but simply seemed to assume that when the plant was photosynthesising a lot it would only respire "a little bit". This seemed to be an intuition rather than a considered proposition. It was almost as if she implicitly assumed that the plant would be fully occupied photosynthesising, and so would put respiration 'on the back burner'.

It seemed Mandy's understanding of the roles of photosynthesis and respiration at that point in her learning was limited by not fully seeing how energy was involved in the two processes (i.e., respiration produces energy, but photosynthesis produces glucose which produces energy), and because she was not considering the need for respiration to support ongoing basic cell functions.