Wood (cork coaster captured with Veho Discovery USB microscope)
Bill was a participant in the Understanding Science Project. Bill (Y7) was explaining that he had been learning about the states of matter, and introduced the notion of there being particles:
So how do you know if something is a solid, a liquid or a gas?
Well, solids they stay same shape and their particles only move a tiny bit
So what are these particles then?
Erm, they're the bits that make it what it is, I think.
Ah. So are there any solids round here?:
Yeah, this table. [The wooden table Bill was sitting at.]
That's a solid, is it?:
Yeah
Technically the terms solid, liquid and gas refer to samples of substances and not objects. From a chemical perspective a table is not solid. A wooden table (such as those in the school laboratory where I talked to Bill) is made of a complex composite material that includes various different substances such as a lignin and cellulose in its structure.
Wood contains some water, and has air pockets, so technically wood is not a solid to a chemist. However, in everyday life we do thing of objects such as tables as being solid.
Yet if wood is heated, water can be driven off. Timber can be mostly water by weight, and is 'seasoned' to remove much of the water content before being used as a construction material. Under the microscope the complex structure of woods can be seen, including spaces containing air.
I think teaching may be a problem here, as when the states of matter are taught it is often not made clear these distinctions only apply clearly to fairly pure samples of substances. In effect the teaching model is that materials occur as solids, liquids and gases – when a good many materials (emulsions, gels, aerosols, etc.) do not fit this model at all well.
Bill was a participant in the Understanding Science Project. Bill was explaining that he had been learning about the states of matter, and introduced the notion of there being particles:
So how do you know if something is a solid, a liquid or a gas?
Well, solids they stay same shape and their particles only move a tiny bit
So what are these particles then?
Erm, they're the bits that make it what it is, I think.
Ah. So are there any solids round here?:
Yeah, this table.
That's a solid, is it?:
Yeah
Technically the terms solid, liquid and gas refer to samples of substances and not objects. From a chemical perspective a table is not solid. However, I continued, accepting Bill's suggestion of a table being solid as a reasonable example.
Okay. So is that made of particles?
Yeah. You can't see them.
No I can't!
'cause they're very, very tiny.
So if I got a magnifying glass?
No.
No?
No.
What about a microscope?
Yeah.
Yeah?
Probably
Possibly?
Yeah, I haven't tried it.
You haven't tried that yet?
No.
But they are very, very tiny are they?
Yeah.
Bill knew that the particles in a solid were very tiny. He seemed to be convinced of their existence, despite not being able to see them. He considered they were too small to be seem with a magnifying glass, but large enough to probably be seen with a microscope.
Bill, like a good scientist, qualified this answer as he had not actually undertaken the necessary observation to confirm this: but his intuition seemed to be that these particles could not be so small that they would not be visible through a microscope.
Later in the interview, Bill used the term microscopic to describe the particles in a solid, where a scientist would describe them as 'submicroscopic' (or 'nanoscopic'):
Tell me the bit about the solids again? Tell me what you said about the particles in the solids?
They move a very tiny amount, but we can't see that … because they are microscopic.
The term 'particle' used in introductory science classes is often used generically to cover atoms, molecules and ion. These entities are usually much too small to be see with an optical light scope (although other instruments such as scanning tunnelling 'microscopes' provide images showing electric potential profiles that can be interpreted as indicating individual atoms).
Students have no real basis on which to understand the scale of atoms and molecules, and often assume they are particles much like the specks and grains that can just be seen. Bill did not make this error, as later in the interview he told me that "the kind of specks of dust, has lots of particles in it, to make up the shape of it".
This becomes important later because much of chemistry supposes that many of the characteristics of substances as observed in the lab. are emergent properties that results from enormous numbers of molecule-scale 'particles' (or 'quanticles') that themselves have quite different behaviour individually.
Well there's three groups, solids, liquids and gases.
So how do you know if something is a solid, a liquid or a gas?
Well, solids they stay same shape and their particles only move a tiny bit.
This point was followed up later in the interview.
So, you said that solids contain particles,
Yeah.
They don't move very much?
No.
And you've told me that ice is a solid?
Yeah.
So if I put those two things together, that tells me that ice should contain particles?
Yeah.
Yeah, and you said that liquids contain particles? Did you say they move, what did you say about the particles in liquids?
Er, they're quite, they're further apart, than the ones in erm solids, so they erm, they try and take the shape, they move away, but the volume of the water doesn't change. It just moves.
Bill reports that the particles in liquids are "further apart, than the ones in … solids". This is generally true* when comparing the same substance, but this is something that tends to be exaggerated in the basic teaching model often used in school science. Often figures in basic school texts show much greater spacing between the particles in a liquid than in the solid phase of the same material. This misrepresents the modest difference generally found in practice – as can be appreciated from the observations that volume increases on melting are usually modest.
Although generally the particles in a liquid are considered further apart than in the corresponding solid*, this need not always be so.
Indeed it is not so for water – so ice floats in cold water. The partial disruption of the hydrogen bonds in the solid that occurs on melting allows water molecules to be, on average, closer* in the liquid phase at 0˚C.
As ice float in water, it must have a lower density. If the density of some water is higher than that of the ice from which it was produced on melting then (as the mass will not have changed) the volume must have decreased. As the number of water molecules has not changed, then the smaller volume means the particles are on average taking up less space: that is, they seem to be closer together in the water, not further apart*.
Bill was no doubt aware that ice floats in water, but if Bill appreciated the relationship of mass and volume (i.e., density) and how relative density determines whether floatation occurs, he does not seem to have related this to his account here.
That is, he may have had the necessary elements of knowledge to appreciate that as ice floats, the particles in ice were not closer together than they were in water, but had not coordinated these discrete components to from an integrated conceptual framework.
Perhaps this is not surprising when we consider what the explanation would involve:
Coordinating concepts to understand the implication of ice floating
Not only do a range of ideas have to be coordinated, but these involve directly observable phenomena (floating), and abstract concepts (such as density), and conjectured nonobservable submicroscopic/nanoscopic level entities.
* A difficulty for teachers is that the entities being discussed as 'particles', often molecules, are not like familiar particles that have a definitive volume, and a clear surface. Rather these 'particles' (or quanticles) are fuzzy blobs of fields where the field intensity drops off gradually, and there is no surface as such.
Therefore, these quantiles do not actually have definite volumes, in the way a marble or snooker ball has a clear surface and a definite volume. These fields interact with the fields of other quanticles around them (that is, they form 'bonds' – such as dipole-dipole interactions), so in condensed phases (solids and liquids) there are really not any discrete particles with gaps between them. So, it is questionable whether we should describe the particles being further apart in a liquid, rather than just taking up a little more space.
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.
Earlier in her interview she had suggested that plus and minus signs represent the charges on neutral atoms when discussing the Na-plus (Na+) and Cl-minus (Cl–) symbols, suggesting an alternative conception of electrical charge in relation to atoms, ions and molecules She gave similar interpretations in the case of K-pus (K+) and F-minus (F–):
Right, okay, so this one here where it's got a K and a plus, what does that represent?
Potassium…An atom that has an extra electron.
Potassium atom, and it's got one extra electron over a full shell
Yeah.
and that's what the plus means, one more electron than it wants?
Yeah.
And what about the F minus?
Represents fluorine which has one, it has an outer shell of seven which has one less electron.
So, for Annie:
K+ referred to the potassium atom (2.8.8.1), not the cation (2.8.8)
and
F– referred to the fluorine atom (2.7), not the fluoride anion (2.8)
Students often present incorrect responses in class (or in interviews with researchers) and sometimes these are simply slips of the tongue or memory, or 'romanced' answer guessed to provide some kind of answer.
When a student repeats the same answer at different times it suggests the response reflects a stable aspect of their underlying 'cognitive structure'. In Annie's case she not only provided repeated answers with the same examples, bit was consistent in the way she interpreted plus and minus symbols across a range of different examples, suggested this was a stable aspect of her thinking.
Physicists see electromagnetism as one of the fundamental forces in the universe, and physics often includes a topic or module on 'electricity and magnetism'. Magnetism can be considered an electrodynamic effect (i.e., due to the movement of charges), but this will not be obvious to students.
Sophia was a participant in the Understanding Science Project. I spoke to here in Y7 (of the English school system) when she told me about the things she had been learning in the topic of electricity. I asked her,
Anything else you've done on electricity?
The er, I don't know what, it's not that much to do with electricity but, yesterday or the day (before) we done magnets.
Oh right. So that's a new topic, is it, not to do with electricity, or?
Well, I think we're still doing electricity. I don't know if it was just something – so we know what might, er, so we know what, what electricity will flow through, and maybe it's something to do with – 'cause magnets like stick to other things, they might be – I'm not sure, I think we might just have had a break from it, I don't know, but.
So, Sophia came up with some suggestions for why magnets might be featured in the electricity topic, but she was not very convinced about this rationale, and considered it was quite possible that the teacher was just interspersing other material to give a 'break' from the main topic. So, instead, they "done magnets".
It is interesting that one of Sophia's suggestions was "what electricity will flow through". The constructivist theory of learning ( read about constructivism here) suggests that meaningful learning involves learners making sense of what they are taught by linking it to their existing ideas and wealth of past experiences. This is a creative process, and sometimes students make unhelpful associations, that can act as learning impediments. Although ceramic magnets are increasingly common, iron, a good conductor, and its alloys, are still used for bar and horseshoe magnets that children will often be familiar with – so this association has potential to be built on constructively.
Of course electricity and magnetism were at one time considered quite distinct phenomena by scientists – and James Clerk Maxwell is rightly remembered for his synthesising theoretical work showing that electricity, magnetism and light could all be understood as manifestations of a single underlying 'phenomenon' of electromagnetism. (Indeed it seems stretching then notion of phenomena to refer to electromagnetism as a single phenomenon, as no one would intuitively perceive its manifestations as being observations of the same phenomenon!) We can hardly expect students to appreciate why electricity and magnetism might be considered a unitary physics topic in school science.
To the science teacher, magnetism is an electrical effect, and electromagnetism is one of the fundamental forces in nature. The unification of electricity, magnetism, and electromagnetic radiation is seen as a major integrative step forwards in science–but our students are not going to see the connections without some help.
When I asked her to tell me what she learnt about magnets she told me that the north pole and the south poles go together because one of them is coming out and one is going in.
Light is actively bounced out of the eye towards objects, so we can see
Keith S. Taber
Sophia was a participant in the Understanding Science Project. Y8 pupil Sophia had been studying sound and light in her school science lessons. Her model of sight involved light entering the eye, but then reflecting out again.
Do you know how you hear and see?
Does the light come in your eye, and it reflects off so you can see. … Just reflects, does it, and bounces on.
So if I've got my eye, some light comes in, some light comes in, what does it do, it bounces where?
About.
Inside the eye?
No around … it bounces out.
And then what?
Then you can see…so you look where you want to see, so it bounces off like in that direction, …you've got to actually look over, …you've got to look that way.
One long-established historical model of sight was based on rays coming from the eyes to detect objects in the outside world. Sophia's model appears to be a hybrid of this historical model, and modern understandings. For Sophia, light does not originate form the eye, but bounds out of it towards the object of sight. The idea that something must come out of the eye for us to see seems to be an intuitive assumption some people make – perhaps because we actually turn out heads and direct out eyes at what we want to focus on. This intuition has potential to act as a grounded learning impediment to learning the scientific model for vision.
It's covalent bonding where the electrons are shared to create a full outer shell
Keith S. Taber
Brian was a participant in the Understanding Chemical Bonding project. He was interviewed during the first year of his college 'A level' course (equivalent to Y12 of the English school system). Brian 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. He was shown a simple representation of a covalent molecule:
Focal figure ('2') presented to Brian
Any idea what that's meant to be, number 2?
Hydrogen molecule.
Why, how do you recognise that as being a hydrogen molecule?
Because there's two atoms with one electron in each shell.
Uh hm. Er, what, what's going on here, in this region here, where these lines seem to meet?
Bonding.
That's bonding. So there's some sort of bonding there is there?
Yeah.
Can you tell me anything about that bonding?
It's covalent bonding.
So, so what's covalent bonding, then?
The electrons are shared to create a full outer shell.
Okay, so that's an example of covalent bonding, so can you tell me how many bonds there are there?
One.
There's one covalent bond?
Yeah.
Right, what exactly is a covalent bond?
It's where electrons are shared, almost, roughly equally, between the two atoms.
So that's what we'd call a covalent bond?
Yeah.
So according to Brian, covalent bonding is where "the electrons are shared to create a full outer shell". The idea that a covalent bond is the sharing of electrons to allow atoms to obtain full electron shells is a very common way of discussing covalent bonding, drawing upon the full shells explanatory principle, where a 'need' for completing electron shells is seen as the impetus for bonding, reactions, ion formation etc. This principle is the basis of a common alternative conceptual framework, the octet rule framework.
For some students, such ideas are the extent of their ways of discussing bonding phenomena. However, despite Brian defining the covalent bond in this way, continued questioning revealed that he was able to think about the bond in terms of physical interactions
Okay. And why do they, why do these two atoms stay stuck together like that? Why don't they just pull apart?
Because of the bond.
So how does the bond do that?
(Pause, c.13s)
Is it by electrostatic forces?
Is it – so how do you think that works then?
I'm not sure.
The long pause suggests that Brian did not have a ready formed response for such a question. It seems here that 'electrostatic forces' is little more than a guess, if perhaps an informed guess because charges and forces had features in chemistry. A pause of about 13 seconds is quite a lacuna in a conversation. In a classroom context teachers are advised to give students thinking time rather than expecting (or accepting) immediate responses. Yet, in many classrooms, 13 seconds of 'dead air' (to borrow a phrase from broadcasting) from the teacher night be taken as an invitation to retune attention to another station.
Even in an interview situation the interviewer's instinct may be to move on to a another question, but in situations where a researcher is confident that waiting is not stressful to the participant, it is sometimes productive to give thinking time.
Another issue relating to interviewing is the use of 'leading questions'. Teachers as interviewers sometimes slip between researcher and teacher roles, and may be tempted to teach rather than explore thinking.
Yet, the very act of interviewing is an intervention in the learners' thinking, in that whatever an interviewer tells us is in the context of the conversation set up by the interviewer, and the participant may have ideas they would not have done without that particular context. In any case, learning is not generally a once off event, as school learning relies on physiological process long after the initial teaching event to consolidate learning, and this is supported by 'revision'. Each time a memory is reactivated it is strengthened (and potentially changed).
So the research interview is a learning experience no matter how careful the researcher is. Therefore the idea of leading questions is much more nuanced that a binary distinction between those questions which are leading and those that are not. So rather than completely avoiding leading questions, the researcher should (a) use open-ended questions initially to best understand the ideas the learner most easily beings to mind; (b) be aware of the degree of 'scaffolding' that Socratic questioning can contribute to the construction of a learners' answer. [Read about the idea of scaffolding learning here.] The interview continued:
Can you see anything there that would give rise to electrostatic forces?
The electrons.
Right so the electrons, they're charged are they?
Yeah. Negatively.
Negatively charged – anything else?
(Pause, c.8s)
The protons in the nucleus are positively charged.
Uh hm. And so would that give rise to any electronic interactions?
Yeah.
So where would there be, sort of any kind of, any kind of force involved here is there?
By the bond.
So where would there be force, can you show me where there would be force?
By the, in the bond, down here.
So the force is localised in there, is it?
The erm, protons would be repelling each other, they'd be attracted by the electrons, so they're keep them at a set distance.
It seemed that Brian could discuss the bond as due to electrical interactions, although his initial ('instinctive') response was to explain the bond in terms of electrons shared to fill electron shells. Although the researcher channelled Brian to think about the potential source of any electrical interactions, this was only after Brian had himself conjectured the role of 'electrostatic forces.'
Often students learn to 'explain' bonds as electron sharing in school science (although arguably this is a rather limited form of explanation), and this becomes a habitual way of talking and thinking by the time they progress to college level study.
Iodine's got a larger force that lithium, so it will pull towards the lithium more
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.
When she was shown an image representing the electron cloud around an iodide ion polarised by an adjacent lithium ion Annie interpreted this as the iodine exerting a greater force on the lithium than vice versa.
Focal figure presented to Annie
What about this, any idea about this?
It's the same sort of thing again – the lithium combines with the iodine – to make a stable outer shell between the two, by sharing electrons, but the lithium has a smaller charge, or smaller pull than the iodine, so the actual shape of it goes in towards. It sort of goes inwards because its attracting the lithium, whereas if the lithium was attracting it, it would be like a reverse picture.
So, so the iodine's attracting what, sorry?
The lithium.
The iodine's attracting the lithium, and the lithium is not attracting the iodine?
Yeah, they're both attracting each other but because this one's got a larger force, then it will pull towards the lithium more.
The iodine's got a larger force,
Yeah.
so it will pull towards the lithium more?
Yeah.
Any image used to represented chemical bonding is necessarily a kind of model, and a partial representation – and there are a range of types of representations students meet. It is perhaps not surprising if students cannot always 'guess what the teacher (or textbook author or researcher) is thinking, and what they intend by a particular type of image.
Annie here demonstrates the common notion that chemical bonding can be based upon 'sharing' electrons (i.e., covalent bonding). At this point in her course Annie would not be expected to appreciate polar bonds or the polarisation of ions, but her prior learning that covalent bonding could be understood as 'sharing' of electrons could potentially act as an impediment to learning that the ionic-covalent bonding distinction should be seen as a spectrum, a continuous dimension, not a dichotomy.
The way forces are understood in physics is that they are interactions between two bodies, and that the same magnitude of force acts of both bodies (i.e., Newton's third law). However, students commonly consider that a 'larger' body (e.g., more massive, more highly charged) exerts a large force on the smaller body. Students do not clearly distinguish the force from its effect, and so this alternative conception seems to draw upon intuitions based on actual experience of the world (i.e., a grounded learning impediment) where larger sources (larger fires, bigger loudspeakers, larger lamps) often seem to have larger effects.
Adrian was a participant in the Understanding Science Project. When I spoke to him during the his first year (Y12) of his 'A level' course he told me he had been studying quantum theory, and I asked him about the name 'quantum theory'. He suggested that a theory is an idea that can be proven, but struggled to suggest any other scientific theories.
What about the theory of evolution? Would you count that as a theory?
Yes, but I am not familiar with it. Was it e=mc²?
That's relativity.
Relativity.
I was thinking evolution?
I don't know that one.
Not sure about evolution at all?
No.
Of course there is more than one theory of evolution, but natural selection was a compulsory topic in the school curriculum, and widely referred to as 'the theory of evolution'. Adrian, however, seemed to have no recollection of hearing about evolution at all. It is inconceivable that he had not met the term in school or elsewhere, but it was not something he was bringing to mind in response to my questioning.
Mohammed was a participant in the Understanding Science Project. When interviewed in the first term of his upper secondary (GCSE) science course (in Y10), he told me he had been learning about ionic bonding in one of his science classes. Mohammed had quite a clear idea about ionic bonding, which he described in terms of the interactions of two atoms where "they both want to get full outer shells", leading to salt which was "like two atoms joined together":
The "two atoms joined together" sounds much like a molecule (and it is very common for students to identify molecule like ion-pairs even in representations of extensive ionic lattices), so I asked Mohammed about this:
Can I see these atoms?
No. They're really small. Because the wavelength of visible light is actually too like large to see the atoms, they just pass over them.
Okay, so I can't see them. But I can imagine them, can I?
Yeah.
So if I could imagine a sodium atom and chlorine atom, and then they form salt, what would it look like afterwards? How could I imagine it afterwards.
Oh it's like two atoms joined together.
That sounds like a molecule to me?
It's not actually, like, joined.
No?
Because I know that whenever things of opposite charge, I know two rods, when they come together, they don't actually touch, so they don't exactly touch, but they are very close, two atoms close to each other
So a molecule would be different to that in some way, would it?
Yeah, a molecule's actually bonded
So how that different?
I think in a molecule, the electron actually slots into spaces.
I see, and it doesn't do that in this case?
No.
So Mohammed thinks that the interaction between the ions will be due to their electrical charges, but, for him, this may not count as a bond, as the forces just hold the ions ("atoms") close together, and do not actually join them. Mohammed's idea of the atoms not actually touching, "they don't actually touch, so they don't exactly touch", is transferring a notion from the familiar world of macroscopic phenomena (where things touch, or they do not touch) to the submicroscopic world of quanticles that do not have definitive size/volume, and do not actually have distinct surfaces, so touching is a matter of degree. There is no more (or less) 'touching' in a covalent bond than in ionic bonding. So according to Mohammed the ions do not form a molecule, as in a molecule there would some kind of more direct joining – he suggests something like an interlocking with electrons from one atom slotting into spaces on another.
Interestingly, Mohammed bases his notion that the ions would not touch on a general principle that he considers to apply whenever considering things of opposite charge – which he justifies on his knowledge that "two [charged] rods, when they come together, they don't actually touch". He may be misremembering something here – or he may have seen a demonstration of suspended charged rods of the same material (so either both negatively or both positively changed) that when one is moved closer to the other the rods repel. Whatever the source, Mohammed seems to feel he has a valid general principle that he can apply here that act as a grounded learning impediment channelling his thinking about the case under discussion along 'the wrong lines'.
Mohammed's notion of the ionic bonding as being just due to forces rather than being a proper bond is very similar to a common alternative conceptions of ionic bonding which sees ions in a lattice only having a limited number of ionic bonds depending upon valency (the valency conjecture) but bonded with other coordination counter-ions by 'just forces' (the just forces conjecture) – although here Mohammed suspected that all ionic bonding fell short of being proper chemical bonds.
This is a very mechanical model of the covalent bond, whereas the scientific model presents bonding as more of a process than a material mechanical link. However teaching models often present bonding this way, and sometimes molecules are modelled in terms of jigsaws with atoms or radicals as pieces to be slotted together. Although such models are only meant to provide a simple analogy for the bonding they may act as learning impediments if learners take them too 'literally' as realistic representations and transfer inappropriate associations from the model to their understanding of the system being modelled.
Mohammed also uses similar language when asked about salt dissolving in water, as the charge of the water forces the sodium and chlorine ions to slot into certain places within the water molecules *.
Mohammed was a participant in the Understanding Science Project. When interviewed in the first term of his upper secondary (GCSE) science course (in Y10), he told me he had been learning about ionic bonding in one of his science classes. Mohammed had quite a clear idea about ionic bonding, which he described in terms of the interactions of two atoms:
And you said in chemistry you've been doing about electron arrangements [electronic configurations], and ionic bonding.
Yeah.
So what's ionic bonding, then?
Ionic bonding is when, like let's say, a sodium atom and take a chlorine atom, which make salt if they react. What happens is – the sodium atom has one electron on its outer shell, and the chlorine atom has seven, now they both want to get full outer shells, so if I er let's say move the electron from the sodium to the chlorine, then the chlorine would have a full outer shell because it would have eight, and because it's lost that shell the sodium will also have eight.
This account of ionic bonding is a common one, although it is inconsistent with the scientific model. A key problem here is that the driving force for bond formation is seen in terms of atoms wanting to complete their electron shells (the 'full shells explanatory principle'). Mohammed's explanation here uses anthropomorphism, as it treats the individual atoms as though they are alive and sentient, acting to meet their own needs – "they both want to get full outer shells".
When Mohammed was probed, he related a full outer shell to atomic stability (a central feature of the full shells explanatory principle).
Okay. How do you know they want full outer shells?
Because it makes them more stable.
Why does it make them more stable?
(pause, c.1 s)
Erm. (Why do electrons?*) (* sotto voce – apparently said to himself)
(pause, c.2s)
Er, because they don't react as much with other elements if they have a full outer shell.
I see.
They don't react.
There is an interesting contrast here between Mohammed's instant response that full shells "makes them more stable", and the long pause as he thought about why this might be so.
His response reflects something quite common in students' explanations n that a student asked why X is the case may respond by explaining why they think X is the case. (That is, as if an appropriate answer to the question "why is it raining so heavily?" would be "because I got soaked through getting here", i.e. actually responding to the question "how do you know that it is raining heavily?")
Such responses seem to be logically flawed, but of course may be a mis-perception of the question being asked (so the learner is answering the question they thought was asked), or (possibly the case here) substituting a response to a related question as a strategy adopted when aware that one cannot provide a satisfactory response to the actual question posed.
The anthropomorphic aspect of his earlier answer was probed:
How do the atoms know that they need to get a full outer shell, they want to get a full outer shell? Do they know about this stability thing?
Not really.
No?
It's just what happens.
Oh, I see, it's just what happens?
Yeah.
So although Mohammed used an anthropomorphic explanation, it seemed he did not mean this literally. (It may seem strange to suggest a 14 year old might consider atoms alive and sentient, but research suggests this is sometimes so!) This has been described as weak anthropomorphism, where the anthropomorphism is only used as a figure of speech. However, such language can act as a grounded learning impediment because if it becomes habitual it can stand in place of a scientific explanation (thus giving no reason to seek a canonical scientific understanding).
Sophia was a participant in the Understanding Science Project. In Y7, Sophia had told me that if molten iron was heated "some of it would evaporate but not all of it, 'cause it's not like water and it's more heavy". She thought only "a little" of the iron would evaporate to give iron vapour: The rest "really just stays as a liquid". [See 'Iron is too heavy to completely evaporate'.]
Just over a year later (in Y8) Sophia had been studying "that different erm substances have different freezing and melting and boiling points, and some aren't like a liquid at room temperatures, some are a solid and some are a gas and things like that".
Give me an example of something else that's a solid at room temperature?
Iron.
Do you think iron would have a melting point?
Yeah.
Yeah, and if I, what would I get if I, if I heated iron to its melting point?
It would become a liquid.
And why would it do that?
Because it's got so hot that particles – they have spread out or something?
So what do you think would happen if I heated the iron liquid?
It would stay a liquid.
No matter how much I heated it?
It might, I don't know if it would become a vapour.
Can you get iron vapour?
No, I don't think so.
You don't think so?
No.
So it seems that Sophia had shifted from accepting that iron would partially evaporate (when learning about the particle model of the different states), to considering that iron (probably) can not become a vapour. The notion of iron as a gas is not something we can readily imagine, and apparently did not seem very feasible. In part this might be because we think of iron the material (a metal, which cannot exist in in the vapour phase) rather than as a substance that can take different material forms.
It seems Sophia's prior knowledge of iron the material was working against her learning about iron the substance, an examples of a grounded learning impediment where prior knowledge impedes new learning.
In Y7 Sophia had seemed to have a hybrid conception where having been taught a general model of the states of matter and changes of state, she accepted the counter-intuitive idea that iron could evaporate, but thought that (unlike in the case of water) it could not completely evaporate . This might have been a 'stepping stone' between not accepting iron could be in the gaseous state and fitting it within the general model that all substances will when progressively heated first melt and then evaporate (or boil) as long as they did not decompose first.
However, it seems that a year later Sophia was actually more resistant to the idea that iron could exist as vapour and so now she thought molten iron would remain liquid no matter how much it was heated. If anything, she had reverted to a more intuitive understanding. This is not that strange: it has been shown that apparent conceptual gains which are counter to strongly held intuitions that are brought about by teaching episodes that are not regularly reinforced can drop away as the time since teaching increases. Conceptual change does not always involve shifts towards the scientific accounts.
[Sophia was in lower secondary school when I talked to her about this: but I was also told by a much older student that the idea of iron turning into a gas sounds weird.]
