learning impediments - Science-Education-Research

Atoms within an element don't need to be bonded …

Atoms within an element don't need to be bonded because they're all the same sort

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. Annie was shown a representation of the close packing of 'atoms' in a metal (with the iron symbol, Fe, shown).

Okay, have a look at number 6…
• • • • • • (pause, c.6 s)
They are obviously iron atoms within an element.
Iron atoms within the element?
Yeah.
Okay. Can you say anything about the arrangement of the atoms?
They're all lined together. They're all close together.
They're closely together, yes, and they're all lined together, there's some sort of regular pattern there okay?
Yeah.
So you think that's in the element, that's a lump of iron, a sort of, a magnified view of a lump of iron.
Yes.

So Annie did recognise the image as representing particles ('atoms') in solid iron. The image showed the particles close together, and Annie was asked if they would hold together – the intention being to find out what, if anything, Annie knew about metallic bonding. Annie did think the atoms would be held together, but she did not suggest this was due to a bond or even a force (cf. "Sodium and chlorine don't actually overlap or anything and would probably get held together by just forces"*).

Do you think those atoms will hold together?
Yes.
Why do you think that is?
Because they're all the same sort.
Does that make them hold together?
Yeah.

So it seemed that Annie held an alternative conception that atoms of the same sort would hold together because they were of the same type. This interpretation was tested.

Yeah? Do you think there is any kind of bonds between the atoms?
• • • • • • • • • (pause, c.9s)
No, because they're all the same and they don't need to be bonded.
Right, okay so recapping…here we've got an example of something where the atoms are all the same, and that holds them together even though there's no chemical bonds.
Yeah.

So Annie held an alternative conception of atomic coherence – that atoms of the same type did not need bonding to hold them together, as being the same kind of atom was sufficient for them to hold together.

It is unlikely that Annie had been taught this idea, and it seems quite possible it is an intuitive idea that might be acting as an example of a 'grounded learning impediment': a notion based on general experience, and inappropriately applied in the context of atomic interactions.

Plants store sunlight

Keith S. Taber

Bill was a Y7 student participating in the Understanding Science project. He used the idea of energy in talking about some aspects of his science. So when considering melting "the particles in (a solid), would have the energy, to move about more, and then it would melt down, because of its melting point, and go into a liquid". Although he could not explain what energy was, he knew "it gives something – the energy to move, it will make something else move or something". He remembered having done some work "where we had to make elastic band powered, 'cause the elastic band stored the energy to make it move", so energy could be stored.

Bill also told me about how in his previous school "we did a lot about plants, and – inside them, how they produce their own food". He explained that "inside, it has leaves, inside it, there is chlorophyll, which stores sunlight, and then it goes, then it uses that sunlight to produce its food. It also uses water from the roots, and the soil, and oxygen in the air. So it needs sunlight, oxygen and water to make its food and live."

However, Bill did not relate this process to the notion of energy, and see that the 'storing sunlight' might have been like the energy stored in an elastic band:

Interviewer: We were talking about energy just now.
Bill: Yeah
I: Do you think that's got anything to do with energy? That process you just talked about?
B: Hm, erm, (pause, c.3 seconds) I'm not sure

So Bill did not make the connection between storing energy, and what he interpreted from his science lesson as 'storing sunlight'. This appears to be an example of a fragmentation learning impediment.

An element needs a certain number of electrons

An element needs a certain amount of electrons in the outer shell

Keith S. Taber

Bert was a participant in the Understanding Science project. In Y10 Bert was talking about how he had been studying electrolysis in class. Bill had described electrolysis as "where different elements are, are taken out from a compound", but it transpired that Bert thought that "a compound is just a lot of different elements put together"*. He seemed to have a tentative understanding that electrolysis could only be used to separate elements in some compounds.

if they're positive and negative then they would be able to be separated into different ones.
So some things are, some things aren't?
Yeah, it matters how many electrons that they have.
Ah. [pause, c.3s] So have you got any examples of things that you know would definitely be positive and negative?
Well I could tell you what happens.
Yeah, go on then.
Well erm, well if a, if an element gives away, electrons, then it becomes positive. But if it gains, then it becomes negative. Because the electrons are negative, so if they gain more, they just go a bit negative.
Yeah. So why would an element give away or gain some electrons? Why would it do that?
Because erm, it needs a certain amount of electrons in the outer shell. It matters on what part of the periodic table they are.
Okay, let me be really awkward. Why does it need a certain number of electrons in the outer shell?
[Pause, c.2 s]
Erm, well, I don't know. It just –

So Bert thought that an element "needs a certain amount of electrons in the outer shell" depending upon it's position in the periodic table, but he did not seem to recall having been given any reason why this was. The use of the term 'needs' is an example of anthropomorphism, which is commonly used by students talking about atoms and molecules. Often this derives from language used by teachers to help humanise the science, and provide a way for students to make sense of the abstract ideas. If Bert comes to feel this is a sufficient explanation, then talk of what an element needs can come to stand in place of learning a more scientifically acceptable explanation, and so can act as a grounded learning impediment.

References to atoms needing a certain number of electrons is often used as an explanatory principle (the full shells explanatory principle) considered to explain why bonding occurs, why reactions occur and so forth.

Bert's final comment in the short extract above seems to reflect a sense of 'well that's just the way the world is'. It is inevitable that if we keep asking someone a sequence of 'well, why is that' question when they tell us about their understanding of the world, they eventually reach the limits of their understanding. (This tendency has been labelled 'the explanatory gestalt of essence'.) Ultimately, even science has to accept the possibility that eventually we reach answers and can not longer explain further – that's just the way the world is. Research suggests that some students seem to reach the 'it's just natural' or 'well that's just the way it is' point when teachers might hope they would be looking for further levels of explanation. This may link to when phenomena fit well with the learner's intuitive understanding of the world, or tacit knowledge.

Bert's reference to an element needing a certain amount of electrons in the outer shell also seems to confuse description at two different levels: he explicitly refer to substance (element), when he seems to mean a quanticle (atom). Element refers to the substance, at the macroscopic level of materials that can be handled in the laboratory, whilst an atom of the element (which might better be considered to gain or lose electrons) is part of the theoretical model of matter at a submicroscopic level, used by chemists as a basis for explaining much macroscopic, observed behaviour of samples of substances.

Electrical resistance depends upon density

Keith S. Taber

Amy was a participant in the Understanding Science project.

Amy (Y10) suggested that a circuit was "a thing containing wires and components which electricity can pass through…it has to contain a battery as well". She thought that electricity could pass through "most things".

For Amy "resistance is anything which kind of provides a barrier that, which the current has to pass through, slowing down the current in a circuit", and she thought about this in terms of the analogy with water in pipes: "we've been taught the water tank and pipe running round it… just imagine the water like flowing through a pipe, and obviously like, if the pipe becomes smaller at one point, erm, the water flow has to slow down, and that's meant to represent the resistance of something".

So for Amy, charge flow was impeded by physical barriers effectively blocking its way. She made the logical association with the density of a material, on the basis that a material with densely packed particles would have limited space for the charge to flow:

So electricity would "not very easily" pass through a wooden bench "because wood is quite a dense material and the particles in it are quite closely bonded".

In air, however, the particles were "not as dense as a solid". When asked if that meant that electricity can pass through air quite easily, Amy replied: "yeah, I think so".

Amy's connection between the density of particles and the ease with which charge could flow is a logical one, but unfortunately involves a misunderstanding of how charge flows through materials, i.e., from a canonical scientific perspective, thinking about the charge flowing through gaps between particles is unhelpful here. (So this can be considered an alternative conception.) This seems to be a creative associative learning impediment, where prior learning (here, the spacing of quanticles in different materials) is applied, but in a context beyond its range of application.

A dusty analogy – a visual demonstration of ionisation in a mass spectrometer

Keith S. Taber

Amy was a participant in the Understanding Science project. She was interviewed when she had just started her 'A level' (i.e., college) chemistry, and one of the topics that the course had started with was mass spectrometry. She gave me a very detailed account of what she had been taught, despite both casting doubt on the logic of parts of the account, and of the accuracy of her own recollection (see Amy's account of mass spectrometry *). One of the unconvincing aspects of the new topic seemed to be the way positive ions were produced by bombarding atoms with (negative) electrons – although she had clearly picked up the point.

She reported that her teacher had demonstrated this point with an analogy. She told me that the teacher was using a lot of analogies, and she seemed to find them a little silly, implying that this analogy was not helpful. This particular example involved a board duster and two matchboxes. One matchbox sat on the duster, and was knocked off by the other matchbox being projected at it.

I thought this was quite interesting, as Amy did think the formation of positive ions was counter-intuitive, but had remembered that this is what happened, and seemed to both remember and understand the use of the analogy – even though she was somewhat dismissive of it. I didn't get the chance to explore the issue at the time, but wondered if this was an example of a student maybe not appreciating the role of models and analogies (and simulation) in science itself, and so feeling that using such a device in teaching science was a little 'naff'.

Amy's explanation of the stupid-sounding bit

Amy was dismissive of the teacher's analogical teaching model, even though she seemed to have remembered what he was illustrating:

I mean there was a couple of bits there that you didn't seem too sure about like, like er you know you sort of, you seemed to almost disown the fact that this electron gun is going to make these things into positive ions, you didn't seem very convinced by that?
Erm – I dunno if it's that I'm not convinced it just sounds weird, because it's like erm (pause, c.2s) I dunno, well it's like it's not something which you can see,
No.
and it's like, I dunno, he did this sort of example using a duster and two matchboxes, and, which wasn't very good, so.(Amy was laughing at this point)
Tell me about that then, how does that work? You see I know a bit about this, I don't know about the duster and the matchboxes.
Like no disrespect to our teacher but he uses these analogies, a duster being an atom with matchboxes being the electrons and something, and them being knocked off, because, yeah.
So he threw a matchbox at a duster that had a matchbox and he knocked the matchbox off the duster?
Pretty much.
See, it works for me,
(Amy laughs)
and you've remembered it?
Well, yeah, but – yeah.
…
Erm, So you've got this neutral atom, and you're firing negative electrons at it?
Yeah.
Now if you say that to somebody who doesn't know anything about what's going to happen, what do you think might happen if you fire negative electrons at a neutral atom?, what might you get?
A negative ion.
That's what you'd expect I think, isn't it, … well obviously you are firing negative things at it, so you will get negative. But in fact that's not what seems to happen. So he was trying to explain to you why firing negative things, at something neutral, you might end up with something positive. 'cause that's not obvious and logical, is it?
Yeah.
So if you throw a matchbox at a duster that contains a matchbox, you might knock the match box off?
Yeah (Amy laughs).

There is clearly a 'cultural' difference here, between the interviewer (a science teacher by background) and the interviewee (the learner), in that the interviewer 'got' the use of the demonstration as a pretty neat physical analogy, whereas the student clearly was dismissive. In this case Amy's lack of engagement with the modelling process did not seem to limit her learning, but her attitude demonstrated a lack of awareness of the status and roles of models in science (and in learning science) which has potential to act as a deficiency learning impediment if she cannot see how teaching models and analogies can help form mental models of scientific systems.

A protein is something which is used for growth and repair

Keith S. Taber

Amy and the role of proteins: a slogan – "proteins are needed for…"

Amy was a participant in the Understanding Science project. Amy was in her first term of 'A level' biology. One of the things she was studying was proteins:

"because proteins do lots of things…they're used for growth and repair, and they form different things like apparently [sic] insulin is a protein"

Amy admitted to be surprised that insulin, which was "made in the pancreas which controls blood glucose levels" should be a protein. She had not expected this "just because you were never told". She has also now learnt that "apparently [sic] haemoglobin is a protein". Amy explained that

"it's just cause like, up until GCSE you're just told that like you know a protein is something which is used for growth and repair, and not that it can be used to make sort of something like insulin"

It seems that at GCSE level (i.e., up to age 16) Amy learnt a slogan relating to the role of proteins – proteins are needed for growth and repair, but a slogan that only related to a processes, without any suggestion of how this might relate to materials and structures. Insulin is considered to be linked to (processes of) sugar regulation, and haemoglobin to (processes of) supplying cells with oxygen. Neither of these processes are seen as growth or repair. It seems 'repair' is primarily understood in terms of damage at the level of tissues, not individual cells or molecules.

This could be considered as an example of a fragmentation learning impediment – the student has not made the link. However, if her school teaching was in terms of the slogan 'proteins are needed for growth and repair', then this could also be seen as a pedagogic learning impediment (a type of grounded learning impediment), as that way of teaching gave Amy a way of thinking about the roles of protein in the body which did not make her receptive to learning that molecules such as insulin and haemoglobin might be proteins.

A reaction is just something that happens?

Keith S. Taber

The term 'reaction' is used in at least two different technical senses in school science: in studying forces as one of the components of a interaction between two bodies such that they each experience a force ('action-reaction'), and as a chemical change which leads to a transformation of matter leading to a new substance(s).

Lomash was a participant in the Understanding Science project. Y7 student 'Lomash' reported that he had been heating materials in a Bunsen flame in his science lessons: "We were burning … coal and copper and things like that, metals."

When he heated copper "It went black…because the flame was too hot, and – it just went black , like paper." The copper stayed black after being removed form the flame, and this was because "it's something else, it's a reaction."

Lomash was using the term 'reaction' in the context of a chemical change – the copper had changed to 'something else', suggesting that he had acquired something of the technical meaning of the term as it is used in chemistry. However 'reaction' is used with a much more general meaning in everyday life, and on further questioning it seemed Lomash has not appreciated the special meaning given to the word in chemistry:

I: So what's a reaction?
L: It's like, a reaction is something that happens.
I: Okay, so if I fell off this stool, would that be a reaction?
L: Yeah.
I: And if you laughed at me falling off the stool, would that be a reaction?
L: Yeah.
I: Oh I see. So that's just another name for something that happens is it?
L: Yeah.

Where students already have meanings for words they come across in school science, they are unlikely to spontanously appreciate how the word is used in a specialised, nuanced way in this particular context. Perhaps Lomash's teacher had emphasised that in heating the copper 'something else' was produced, making the observed change a 'reaction'. Certainly Lomash happily accepted this was a reaction, but apparently only in his existing vague everyday sense of the term. His existing linguistic association for the term 'reaction' appeared to act as an associative learning impediment.

Read about learners' alternative conceptions

A molecule is a bit of a particle – or vice versa

Keith S. Taber

Tim was a participant in the Understanding Science project. When I talked to Tim during the first term of his 'A level' (college) course, he had been studying materials with one of his physics teachers. He referred to molecules in wood (suggesting the analogy that molecules are like a jigsaw)*, and referred to a molecule as "a bit of a particle",

I: So what's a molecule?
T: Erm it's like a bit of a particle, so, something that makes up something.

He then went on to refer to how malleability depended upon atoms "because it's just what they're made out of, it's different things to make it up, different atoms and stuff". His understanding of the relationship between atoms and molecules was probed:

Ah, so we've got atoms?
Yeah.
Not molecules?
(Pause, c.2s)
This is something different this time?
Yeah.
Oh, okay, tell me about atoms.
I think, I think atoms make up molecules, which make particles. Well there's them three things, but I'm not entirely sure what order they go in, and I think atoms are the smallest one.
So we've got, these three words are related, are they, atoms, molecules, particles?
Yeah.
You think there is a relationship there?
Yeah.
And, what, they are similar in some way, but not quite the same, or?
Erm, yeah I think it's like order of size.
You think atom's the smallest?
Yeah.
And bigger than an atom you might have?
A molecule. No a particle, then a molecule, I think.
Yeah, is that the same for everything do you think? Or, are some things molecules, and some things atoms, and some things particles?
(Pause, c.2s)
I think it's the same, I think it all goes – like that.

The term 'particle' is ambiguous in school science. Sometimes by particle we mean a very small, but still macroscopic objects, such as a salt grain or a dust speck. However, often, we are referring to the theoretical submicroscopic entities such as atoms, molecules, ions, neutrons etc, which are components of our theoretical models of the structure of matter. (These particles, behave in ways that are sometimes quite unlike familiar particle behaviour because of the extent to which quantum effects can dominate at their scale. The term 'quanticle' has been proposed as a collective term for these particles.) Students are expected to know which usage of 'particles' we might mean at any given time.

Tim assumes to have misunderstood how the term particle is used (as a collective term) when used to describe quantiles, and so has come to the understanding that at this level there are three different categories of quanticle based on relative size: the atoms (the smallest), and also molecules and particles which are larger than atoms, but which he is unsure how to relate.

The use of the everyday word particle to refer to theoretical submicroscopic entities by analogy with the more familiar everyday particles is very clear to scientists and science teachers, but can act as an associative learning impediment to learners who may think that quanticle particles are just like familiar particles, but perhaps quite a lot smaller. In Tim's case, however, it seems that a different 'learning bug' had occurred. Presumably he had commonly come across the use of the terms 'atom', 'molecule' and 'particle' in science lessons to describe the components of matter at the submicroscopic level, but had not realised that particle was being used as a generic term rather than describing something different to atoms and molecules.

During his years of school science Tim had constructed a different 'ontology' of the submicroscopic constituents of matter to that expected by his teachers.

Read about learners' alternative conceptions

A compound is just a lot of different elements put together

Keith S. Taber

Bert was a participant in the Understanding Science project. When interviewed in Y10 he reported that he had been studying electrolysis in chemistry:

"that's where different elements are, are taken out from a compound…there's a positive anode and a negative cathode. And what it does it attracts the positive part of the compound to the negative cathode, and the negative part goes to the positive , to, you know, so that they can erm get the different elements in the different places, so they can just have one element on its own".

To fully understand what this means from a chemical context the learner needs to appreciate the chemical distinction between elements, compounds and mixtures, so I asked Bert what he thought a compound was:

It's erm, it's er two, er you know, it's just a lot of different elements put together – to create just one.
So if I went and got some elements, let's say I went and got a little file of carbon, a little file of sulphur, a little file of copper, er a little file of magnesium and I were to mix them into a beaker, maybe get a glass rod, give it a good stir, er, give me a compound?
Erm, so it's carbon, erm, carbon, sulphur, magne¬. Carbon, er – What's the fourth one?
Carbon, sulphur, magnesium and copper I think I said.
And copper. All right, erm. Copper, copper sulphate and – and carbon, and I think carbon and magnesium might go just as elements.
Okay, so if I ignored the carbon and magnesium,
Yeah.
if I took some copper and some sulphur,
Yeah.
and mixed them up together,
Yeah.
then I'd get copper sulphate.
Yeah.
And that's a compound now?
Yeah.

In chemistry there is a crucial difference between a mixture and a compound: one which it appeared Bert had not at this point acquired. Presumably his chemistry teacher, in teaching the topic of electrolysis was assuming students in the class would apply prior learning about the difference between elements and compounds, so as to appreciate the significance of electrolysis as a technique which brings about an energetically unfavourable chemical change. This prerequisite knowledge appeared to be lacking for Bert, which provided a deficiency learning impediment when it came to understanding the teaching on electrolysis.

Read about learners' alternative conceptions