Sandstone looks like it's made out of a load of sand stuck together
Sophia was a participant in the Understanding Science Project. Sophia (when a Y8 pupil) had been learning in class about different kinds of rocks, including
rocks that erupt from volcanoes,
rocks that are formed underground, and
rocks that 'come from mountains' that 'get worn away':
When rocks … come from mountains, they like get worn away.
Mm, so what happens when you wear away the rock then?
Does it go like into a river, like a spring, and then gets carried – down, and gets smaller….when it gets tiny, tiny would it turns into sand?
And then what happens to the sand, it just stays as sand does it?
Prob¬ [Probably]… Yeah. …
Have you heard of a kind of rock called sandstone?
Yeah.
Any idea, what sandstone is?
It's sand like, on the rock, it just looks like it's made out of a load of sand stuck together.
Despite having been taught about the three categories of rock formed in different ways, Sophia had apparently only remembered the erosion stage in formation of the sedimentary rocks.
Erosion leads to rocks being broken down into sand. And sandstone 'looked like' it was made of a lot of 'sand stuck together', but for Sophia this seemed to be little more than a coincidence. She did not make the expected connection.
This seems to be an example of a fragmentation learning impediment, where the learner does not perceive the relevance of prior learning, and so does not use it to interpret teaching in the way intended by the teacher. So, here there was a lack of conceptual integration with material that was meant to be related being learnt as discrete facts.
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.
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?
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.
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.
Energy can be made, but only in biology: Amy had learnt that respiration was converting glucose and oxygen into energy – but had learnt in physics that energy cannot be made
Amy was a participant in the Understanding Science Project. Amy was a Y10 (14-15 year old) student who had separate lessons in biology, chemistry and physics. When I spoke to her (see here), she had told me that respiration was "converting glucose into energy and either carbon dioxide and lactic acid, or just carbon dioxide". When I spoke to her again, some weeks later, Amy repeated that respiration was "converting oxygen and glucose into energy and carbon dioxide…it produces energy" ; that trees "need to produce energy and when they photosynthesise they produce like energy"and that food is "broken down and converted into energy".
Later in the same interview I asked her about her physics lessons, where she had been told that "there's like different types of energy" and that it "cannot be made or destroyed, only converted". Amy did not seen to have recognised any conflict between how she understood the role of energy in biology, and what she was taught in physics.
However, on further questioning, she seemed able to recast her biology knowledge to fit what she had been taught in physics:
So in physics, they tell you (that) you cannot make or destroy energy.
Yeah.
And in biology, they tell you that you can make energy from oxygen and glucose?
(No response – Pause of c.2 seconds)
But only in biology, not in physics?
Oh, erm, I suppose the energy, erm well in respiration, erm the energy must be converted from stored energy in food.
So in an interview context, once the linkage was explicitly pointed out, Amy seemed to recognise that the principle learnt in physics should be applied in biology. However, she did not spontaneously make this link, without which the nature of respiration was misunderstood (in terms of energy being created from matter). This would appear to be an example of a fragmentation learning impediment, as although Amy had learnt about the conservation of energy she did not immediately how this related to what she had studied in biology, about respiration.
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.
Bill was a participant in the Understanding Science Project. Bill (a Year 7 pupil) told me that "solids they stay same shape and their particles only move a tiny bit". He explained that the 'particles' were "the bits that make it what it is", although "you can't see them" as "they're very, very tiny". Later he commented that "they are microscopic".
Although it is very common for such particles to be said to be 'microscopic', a better term would be 'nanoscopic'. Microscopic suggests visible under a microscope, and the particles referred to here ('quanticles') are actually submicroscopic." The term microscopic could therefore be misleading, and it is known that often when students first learn about particles in science they often have in mind small grains of powder or dust.
Bill explained that "there is particles in everything". Bill was able to talk a lot about particles in solids, liquid and gases and explain what happened during melting.
Later in the same interview Bill talked about how in his primary school he had studied "a lot about plants, and – inside them, how they produce their own food", and how "inside, it has leaves, inside it, there is chlorophyll, which stores [sic] sunlight, and then it uses that sunlight to produce its food."
I asked Bill if plants had anything to do with particles:
Well in the plant, there is particles….'cause it's a solid…. 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.
Bill explained that "…in the leaves it is chlorophyll which is a green substance, so that would make, give it its colour".
Do you think chlorophyll is made of particles?
Hm, don't know.
So it seemed that although 'there is particles in everything', Bill did not seem to feel this meant that he could apply the particle idea to all substances. This could be an example of a fragmentation learning impediment: that is, where learning in one area is not recognised as relevant in studying other subjects or topics.
