Former school and college science teacher, teacher educator, research supervisor, and research methods lecturer. Emeritus Professor of Science Education at the University of Cambridge.
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.]
Some molten iron would evaporate but not all of it, 'cause it's not like water and it's more heavy
Keith S. Taber
Sophia was a participant in the Understanding Science Project. In her first interview near the start of Y7, Sophia told me that she had learnt "about the particles…all the things that make – the actual thing, make them a solid, and make them a gas and make them a liquid" (i.e. the states of matter). All solids had particles, including (as examples) ice and an iron clamp stand. There would be the same particles in the ice as the iron.
"because they are a solid, but they can change , 'cause if erm they melted they would be a liquid so they would have different particles in…Well they are still the same particles but they are just changing the way they act".
Sophia's suggestion that particles in ice and the iron were the same types of particles as both were solid seems to be 'carving nature' at the wrong joints – that is in this model the particles in ice and (solid) iron would be of one type, whilst those of water and liquid iron would be of another type (that is she had an alternative ontology). Sophia quickly corrected this, so it is not clear if this reflected some intuitive idea or was just 'a slip of tongue'.
According to Sophia the ice could be melted "with something that's hot, like a candle" but for the iron "you need more heat, 'cause it's more, it's a lot more stronger…because it's got more particles pushed together".
Sophia's explanation suggested a causal path (right-hand side) quite different from a canonical causal path (left-hand side)
Strictly the difference is more about the strength of the interactions between particles, than how many were pushed together – although strong bonding forces would tend (all other factors being equal) to lead to particles being bound more tightly and being closer. We might argue here that Sophia seemed to confuse cause and effect – that a higher density of particles was an effect of strong bonding, which would also mean more energy was needed to overcome that bonding. (However, we should also be aware that when students use 'because' (which formally implies causality) they sometimes mean little more than 'is associated with'.)
If the water obtained from melting ice was heated more "it will evaporate into the sky". However, if the molten iron was heated Sophia thought that "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:
"No, I think that water all of it goes, but other material, other liquids some of it will go, not all of it". The rest "if it's cold enough, it will go back into a solid, but if not it really just stays as a liquid".
Sophia's idea that no matter how much liquid iron was heated it would not completely evaporate so some would remain liquid, which seemed to be linked in her mind to its density, seems to be evidence of an alternative conception. Students may not expect that something as (apparently) inherently solid as iron could evaporate (everyday experience may act as a grounded learning impediment), and so may not readily accept that the basic model of the states of matter and changes of state (i.e., a heated liquid will evaporate or boil) can apply to something like iron. Sophia seemed to have formed a hybrid conception – applying the taught model, but with a modification reflecting the counter-intuitive notion that iron could become a vapour.
Conceptual change can be a slow progress, although hybrid conceptions may be 'stepping stones' towards more scientific understandings. However, when I spoke to Sophia in Y8 she did not seem to have progressed further. [See 'Liquid iron stays a liquid when heated'.]
One of the things I have noticed in recent news reports about the current pandemic is the tendency to justify our susceptibility to the COVID-19 coronavirus by praising the virus. It is an intelligent and sneaky foe, and so we have to outwit it.
But no, it is not. It is a virus. It's a tiny collection of nucleic material packaged in a way that it can get into the cells which contain the chemical resources required for the virus to replicate. It is well suited to this, but there is nothing intelligent about the behaviour. (The virus does not enter the cell to reproduce any more than an ice cube melts to become water; or a hot cup of coffee radiates energy to cool down; or a toddler trips over to graze its knee rather than because gravity acts on it.) The virus is not clever nor sneaky. That would suggest it can adapt its behaviour, after reflecting upon feedback from its interactions with the environment. It cannot. Over generations viruses change – but with a lot of variations that fail to replicate (the thick ones in the family?)
Yet any quick internet search finds references to the claimed intellectual capacities of these deadly foes. Now of course an internet search can find references to virtually anything – but I am referring to sites we might expect to be authoritative, or at least well-informed. And this is not just a matter of a hasty response to the current public health emergency as it is not just COVID 19, but, it seems, viruses generally that are considered intellectually superior.
Those smart little viruses
The site Vaccines Today has a headline in a posting from 2014, that "Viruses are 'smart', so we must be smarter", basing its claims on a lecture by Colin Russell, Royal Society University Research Fellow at Cambridge University. It reports that "Dr Russell says understanding how 'clever' viruses are can help us to outsmart them". (At least there are 'scare quotes' in some of these examples.)
An article from 2002 in an on-line journal has the title "The contest between a clever virus and a facultatively clever host". Now I have moaned about the standard of many new internet journals, but this is the Journal of the Royal Society of Medicine, and the article is in volume 95, so I think it is safe to apply the descriptor 'well-established' to this journal.
A headline in Science news for Students (published by Society for Science & the Public) from 2016 reads "Sneaky! Virus sickens plants, but helps them multiply". I am sure it would not take long to find many other examples. An article in Science refers to a "nasty flu virus".
Sneaky viruses
COVID-19 is a sneaky virus according to a doctor writing in the Annals of Internal Medicine. Quite a few viruses seem to be sneaky – the the human papillomavirus is according to an article in the American Journal of Bioethics. The World Health Organisation considers that a virus that causes swine fever, H1N1, is sneaky according to an article in Systematic Reviews in Pharmacy, something also reported by the BMJ.
There are many references in the literature to clever viruses, such as Epstein‐Barr virus according to a piece in the American Journal of Transplantation. The Hepatitis C virus is clever according to an article in Clinical Therapeutics.
Science communication as making the unfamiliar, familiar
Science communication is a bit like teaching in that the purpose of communication is often to be informative (rather than say, social cohesion, like a lot of everyday conversation {and, by the way,it was another beautiful day here in Cambridgeshire today, blue sky – was it nice where you are?}) and indeed to make the unfamiliar, familiar. Sometimes we can make the unfamiliar familiar by showing people the unfamiliar and pointing it out. 'This is a conical flask'. Often, however, we cannot do that – it is hard to show someone hyperconjugation or hysteresis or a virus specimen. Then we resort to using what is familiar, and employing the usual teacher tricks of metaphor, analogy, simile, modelling, graphics, and so forth. What is familiar to us all is human behaviour, so personification is a common technique. What the virus is doing, we might suggest, is hijacking the cell's biochemical machinery, as if it is a carefully planned criminal operation.
Strong anthropomorphism and dead metaphors
This is fine as far as it goes – that is, if we use such techniques as initial pedagogic steps, as starting points to develop scientific understanding. But often the subsequent stage does not happen. Perhaps that is why there are so many dead metaphors in the language – words introduced as metaphors, which over time have simple come to be take on a new literal meaning. Science does its fair share of borrowing – as with charge (when filling a musket or canon). Dead metaphors are dead (that is metaphorical, of course, they were never actually alive) because we simply fail to notice them as metaphors any more.
There are probably just as many references to 'clever viruses' referring to computer viruses as to microbes – which is interesting as computer viruses were once only viruses metaphorically, but are now accepted as being another type of virus. They have become viruses by custom and practice, and social agreement.
Whoever decided to first refer to the covalent bond in terms of sharing presumably did not mean this in the usual social sense, but the term has stuck. The problem in education (and so, presumably, public communication of science) is that once people think they have an understanding, an explanation that works for them, they will no longer seek a more scientific explanation.
So if the teacher suggests an atom is looking for another electron (a weak form of anthropomorphism, clearly not meant to be taken too seriously – atoms are not entities able to look for anything) then there is a risk that students think they know what is going on, and so never seek any further explanation. Weak anthropomorphism becomes strong anthropomorphism: the atom (or virus) behaves like a person because it has needs and desires just like anyone else.
Perhaps in our current situation this is not that important – the public health emergency is a more urgent issue than the public understanding of the science. But it does matter in the long term. Viruses are not clever – they have evolved over billions of years, and a great many less successful iterations are no longer with us. The reason it matters is because evolution is often not well understood.
As an article in Evolution News and Science Today (a title that surely suggests a serious science periodical about evolution) tells us again that "Viruses are, to all appearances, very clever little machines" and asks "do they give evidence of intelligent design" (that is, rather than Darwinian natural selection, do they show evidence of having an intelligent designer?) After exploring some serious aspects of the science of viruses, the article concludes: "So it seems that viruses are intelligently designed" – that is, a position at odds with the scientific understanding that is virtually a consensus view based on current knowledge. Canonical science suggests that natural processes are able to explain evolution. But these viruses are so clever they must surely have been designed (Borg technology, perhaps?)
This is why I worry when I hear that viruses are these intelligent, deliberate agents that are our foes in some form of biological warfare. It is a dangerous way of thinking. So, I'm concerned when I read, for example, that the cytomegalovirus is not just a clever virus but a very clever virus. Indeed, according to an article in Cell Host & Microbe "CMV is a very clever virus that knows more about the host immune system and cell biology than we do". Hm.
1. The subheading was amended on 4th October 2021, after it was quite rightly pointed out to me that the original version, "COVID-19 is not a clever or sneaky virus (but it is not dumb either)", incorrectly conflated the disease with the virus.
In a sponge, the particles are spread out more, so it can absorb more water
Keith S. Taber
Morag was a participant in the Understanding Science Project. In her first term of secondary school, she told me that he had learnt about particles. Morag had explained, and simulated through role play for me, the arrangements of particles in the different states of matter (See: So if someone was stood here, we'd be a solid.) She had also emphasised just how tiny the particles were, "little, little-little-little things", and so how many there were in a small object: "millions and millions and millions". This suggested she had accepted and understood the gist of the scientific model of submicroscopic particles.
Yet as the conversation proceeded, Morag suggested the macroscopic behaviour of sponge in absorbing water could be explained by the arrangement of particles leaving space for the water. This is perhaps a reasonably, indeed quite imaginative, suggestion at one level, except that the material of a sponge is basically solid (where, as Morag recognised, that the particles would be very close together). A sponge as whole is more like a foam, with a great volume of space between the solid structure (where air can be displaced by liquid) and an extensive surface area.
Do you think it is important to know that everything is made of particles?
No.
It's not important?
Well it could be important, but it's not that important. Well, you see, like that [indicating the voice recorder used to record the interview] has got like lots and lots of particles pushed together this [Morag gestures]…But a sponge, the particles are like, the particles are more kind of like, they're still the same, but it's just spread out more, so it can absorb more water.
Oh I see, so are you saying that the same particles are in my little recorder, as in the sponge.
Yeah, they're the same, but there's just more of them in one than there would be in the other.
The failure here is perhaps less Morag's inappropriate explanation, than the tendency to teach about the ideals of solids, liquids and gases, which strictly apply only to single substances, where most real materials students come across in everyday life are actually mixtures or composites where the labels 'solid', liquid' and 'gas' are – at best – approximations.
Teaching has to simplify complex scientific ideas to make them accessible to students of different ages, so often teaching models are used. But sometimes simplifications can cause misunderstandings, and so the development of alternative conceptions. If 'everything is a solid, liquid or gas' is used as a kind of teaching model, or even presented as a slogan or motto for students to echo back to the teacher, when lots of things students come across in everyday life (e.g., butter, clouds, the pet cat – a bathroom sponge) do not easily fit these categories, and this is likely to lead to students overgeneralising.
Although it is often not possible to assign a single simple cause to a student's flawed thinking, this could be considered likely to be an example of a pedagogic learning impediment (a type of grounded learning impediment) in chemistry: a case where an approach to teaching can lead students' thinking in unhelpful directions.
Mohammed was a participant in the Understanding Science Project. When Mohammed was near the end of his first term of upper secondary science (in Y10) he told me that in his chemistry lessons he had been studying atoms and ionic bonding. When I asked him what an atom was, he suggested that an atomis the smallest amount of matter you can get[*] as well as being "it's the building block of all matter".
The notion that atoms are the smallest components of matter has a strong historical pedigree – but the modern idea of the atom is unlike the solid and indivisible (= atomos: uncuttable) elementary particles imagined by some Greek philosophers. Modern atoms are considered complex structures, and may be dismantled.
It is not unusual for students to suggest that atom is the smallest thing that one can get, and then go on to describe atomic structure in terms of smaller components! The idea that the atom is the smallest thing possible (a kind of motto or slogan) is commonly adopted and then retained despite learning about subatomic particles.
Mohammed, however, justified his suggestion that an atom was "the smallest amount of matter you can get" by arguing that "matter is something that is built out of protons, neutrons and electrons". So Mohammed's notion of what counted as 'matter' (an ontological question) was at odds with the scientific account
Mohammed did not suggest that matter had to have overall neutrality, and his suggestion that matter is something that is built out of protons, neutrons and electrons had to be amended when he realised it would exclude hydrogen atoms as being matter:
So what if I had a balloon full of hydrogen gas, would that, would the hydrogen be matter?
Yeah.
So would that consist of protons, neutrons and electrons?
No it wouldn't. Sorry, can I take away the neutrons
Okay, so matter's what then? What's our new definition of matter?
Protons, electrons.
Mohammed presented his responses with confidence and without hesitation, which seemed to suggest he was offering well established ideas. However, he did not seem to have fully thought through these ideas, and perhaps was constructing a rationale in situ in the interview. The logical consequences of Mohammed's new definition was that atoms and ions would be considered matter but not nuclei or electrons.
What if I had sodium. Do you think that would be matter?… if I had a lump of sodium, would that be matter?
Yeah
And why is that matter?
Because it has, it has a full atom, it has protons, neutrons, electrons, even though you can have no neutrons.
Okay, but it has to have the protons and the electrons?
Yeah.
Now what if I just had one atom of sodium, would that still be matter?
Yeah.
…so let's say I've got my atom, with my eleven protons, and my probably twelve neutrons I think usually. And I've got eleven electrons round the outside. If I take take one of the electrons off this atom, it's not an atom any more is it?
It's an ion.
Now is it still matter?
Yeah.
Because I've still got protons and electrons. What if I took a second electron off, could I take a take second electron off?
Yeah.
What have I got then, then?
You've still got matter.
What if I took a third one off?
Well if you, if you just take all of them off, then you'd stop having matter.
So if I've got eleven electrons, can I take ten of them off?
Yeah.
And I'd still have matter?
Yeah.
The idea of what counts as matter here seems a rather idiosyncratic alternative conception (rather than being a common alternative conception that is widely shared). Science teachers would probably consider that all material (sic) particles are matter, and – perhaps – that this should be obvious to students. However, the submicroscopic realm is far from everyday experience so perhaps it is not surprising that students often form their own alternative conceptions.
Sophia was a participant in the Understanding Science Project. Sophia (then in Y7) had been burning materials in science. She had burnt some paraffin in a small burner (a glass burner with a wick). Her understanding of the process was not in terms of a chemical reaction, but at a more 'phenomenological' level:
So what happens to paraffin when it burns then?
It keeps on burning… but you, you can put it out easily as well…. we just blew it out…
I see, but otherwise it just carried on burning, did it? Did it carry on burning for ever, if you don't blow it out?
No, 'cause it would run out.
What would it run out of?
The paraffin.
So where does the paraffin go then?
(There was a pause, of about 4 seconds. Sophia laughs, but does not offer answer.)
And what happens to the level of the paraffin in the burner?
It gets lower and lower.
So why's that, what's happened to it?
'cause you are using all of it up, when it's burning.
So it get all used up does, it – so what happens when it's all used up?
You have to refill it.
So for Sophia the burning of paraffin is not seen in terms of basic chemistry (what happens to the substance paraffin during the process of burning?), but rather she seems to interpret what she has seen in terms of everyday ideas – stuff, such as fuels, get used up – if we use it, we no longer have it.
The final question in this sequence ('what happens when it's all used up') is not treated in scientific terms (e.g., from the perspective of the conservation of matter, there is an issue of where the 'stuff' what was the paraffin has gone), but in practical terms: when we use up the fuel in the burner, we need to refill it to do more burning.
Here, understanding in 'everyday' or 'lifeworld' terms seems to dominate her thinking: the familiar idea that things get used-up obscures the scientific question of what happens to the matter in the fuel. Presumably, her teacher wanted her to focus on the scientific perspective, where burning is combustion, a type of chemical change, but it appears her life-world perspective acted as a grounded learning impediment – an existing way of thinking about a phenomenon that is taken for granted and obscures the scientific perspective.
The everyday way of understanding the world could be called the natural attitude. It seems that for Sophia it is 'just natural' that fuels get used up, and so there is nothing there to explain. Arguably, the work of a science teacher sometimes involves persuading students to seek explanations for things they had considered 'just natural', and so not in need of explanation.
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.
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, she told me that in biology she was studying respiration which she suggested was "converting glucose and oxygen into energy…through anaerobic respiration and aerobic respiration". This involved "converting glucose into energy, glucose and oxygen into energy and either carbon dioxide and lactic acid, or just carbon dioxide. Something like that".
In physics lessons she had been studying the topic of electricity, and she recognised that energy was an idea which appeared in both topics:
The work in physics on electricity and the work in biology on respiration, is there any connection there?
Well, in respiration energy is produced, and in physics energy is stored in a battery or a power supply and that then travels round – the circuit.
When I spoke to her again, some weeks later, Amy repeated that respiration was "converting oxygen and glucose into energy and carbon dioxide". She told me that this was important "because it produces energy which like in humans your body needs, well in anything, your body needs and to grow and move and things like that". She also told me that trees were "living and they need to produce energy and when they photosynthesise they produce like energy anyway" but that she obtained energy "through food which is then broken down and converted into energy".
It is a basic principle in science, that energy cannot be created or destroyed. (Since Einstein, is has become clear that strictly matter can be considered as if a form of energy, and interconversion can take place, for example in nuclear processes, but this effect is negligible in normal chemical systems.) What Amy took away from her biology classes, though, was that energy could be produced in respiration and photosynthesis, and that indeed glucose and energy were converted into energy in respiration (i.e., an alternative conception). Amy did not seem to be applying the principle of energy conservation here – although it transpired (see here) that she had recently studied this in her physics lessons.
Carbon electrons will have more mass and charge than chlorine electrons
Keith S. Taber
Annie was a participant in the Understanding Chemical Bonding project. She was interviewed near the start of her college 'A level' course (equivalent to Y12). She was shown a representation of a tetrachlomethane molecule.
When Annie was asked about the diagram, she was not sure if the differently represented electrons would actually be different from each other, She suggested that perhaps electrons from different atoms would actually contain some of the particular element. Annie seemed unsure where one could tell the difference between electrons from different atoms, but her intuition seemed to tell her they should be different,
Under further questioning, Annie was able to suggests ways in which carbon electrons would be different from chlorine electrons. Most science teachers may expect it would be quite obvious that one electron is much like another one in terms of essential properties (e.g., charge, rest mass). We probably assume students will readily appreciate this, and perhaps that it is not a point that needs to be emphasised. We might expect a student would immediately reject any suggestion that electrons from different atoms should be fundamentally different.
Do you think they would be the same size, electrons from carbon and electrons from chlorine?
No.
Which ones will be bigger, do you think?
The carbon ones.
Do you think they're the same charge? The same electrical charge?
No.
(pause, c.5)
No, which one do you think will have a bigger charge?
(pause, c.2s)
The carbon.
…
Yeah, what about colour. What colour do you think they will be?
Colours. What of the actual electrons?
Mm.
Mm, (pause, c.5s) I don't think they'd really have a colour, but I think if they had to have a colour, then they'd pick out the colour from the element.
A teacher is likely to expect an A level student to appreciate that all electrons are intrinsically the same. Annie seemed to think that the electrons of different atoms were different, somehow reflecting the particular element, and open to the idea they may differ in mass and charge, and possibly even colour.
Whilst Annie's comments are at odds with canonical science, they reflect thinking that is quite common among learners who often fail to appreciate the core principle of sub-microscopic models of matter, i.e., that the emergent properties of matter at macroscopic scale are explained in terms of the different properties of the tiny particles (i.e., quanticles) from which matter is conjectured to be constituted at a much finer scale. She was not keeping clearly distinguished macroscopic properties (such as colour) and properties that sub-atomic particles could have.
Electrons from different elements would be different – perhaps because they would actually contain some of the element in the electron?
Keith S. Taber
Annie was a participant in the Understanding Chemical Bonding project. She was interviewed near the start of her college 'A level' course (equivalent to Y12). She was shown a representation of a tetrachlomethane molecule.
When Annie was asked about the diagram, she noted that (following a representational convention) the electrons were represented differently. Using different symbols like this is quite common, but is little more that a bookmaking tool – to help keep count of the number of electrons in the molecule in relation to those that would be present in discrete atoms.
…are there any bonds [shown] in that diagram do you think?
Yes.
How many?
Four.
Four bonds, so we've got four bonds there. Erm, are the bonds actually shown?
Yeah.
So how are they represented on the diagram?
By the circles that overlap, and they're showing it by the electrons, the outer-shell electrons in the chlorine have got black dots and the ones from carbon have got just circles.
Okay. So the carbon electrons and the chlorine electrons are signified in a different way
Yeah.
I followed up this point to check Annie understood that the convention did not imply that there was any inherent difference between the electrons.
So what would be the difference between a carbon electron and a chlorine electron?
(pause, c.5s)
The expected answer here was 'no difference', but the pause suggested Annie was not clear about this. So I set up an imaginary scenario, a kind of thought experiment:
If I gave you a bottle of electrons – which I can't do – how would you be able to tell chlorine electrons from carbon electrons – in what ways would they be different?
They would be different because, erm, I don't know if they would actually contain some of the element in the electron.
Do you think they might have little labels on some with "C"s and some with "Cl"s or
Yeah, I don't know if you got an electron, and you could sort of if you took one single one you could say, right that's chlorine and that one's carbon.
You are not sure, you are not sure if you could, or not?
No.
The idea that an electron might contain some of the element seems to miss the key idea that macroscopic phenomena (samples of element) are considerer to energy from extensive ensembles of submicroscopic particles ('quanticles').
Annie did not seem too sure here – perhaps her intuition was that a carbon electron would be different to a chlorine electron, but she could not suggest how. Electrons have no memories, and there is no way of knowing whether an electron has previously been part of a particular atom (or ion or molecule). A free electron is not meaningfully a chlorine electron or a carbon electron. However, students do not always appreciate this, and may consider that free electrons in some sense belong to an atoms they they derived form, and even that this may later have consequences (as with the 'history' conjecture in thinking about ionic bonding).
In my work I've spent a lot of time analysing the things learners say about science topics in order to characterise their thinking. Although this work is meant to have an ethnographic feel, and to be ideographic (valuing the thinking of the individual in its own terms), there is always an underlying normative aspect: that is, inevitably there is a question of how well learners' conceptualisations match target curricular knowledge and canonical science. We all have intuitions which are at odd with scientific accounts of the world, and we all develop alternative conceptions – notions which are inconsistent with canonical concepts.
Peter and Patricia started seeing each other at this local fence earlier this year.
Soon passion got too much for them and they (publicly) consummated their relationship on this very fence (some birds have no shame).
It is easier to spot this in others (you think what?!) than it is in ourselves. But occasionally you may reflect on the way you think about a topic and recognise aberrations in your own thinking. One of these examples in my own thinking relates to bird's nests. I know that birds build nests as a place to lay and hatch eggs. Using the ground would be very dangerous due to vulnerability to predators. Simply using branches would be precarious – especially as eggs are hardly best shaped to be balanced on a tree branch. I also know that once the young are fledged have fled the nest, it has outlived its purposes.
They quite liked the area, and decided to look for a place nearby.
Soon they had identified a nice place to build their new home in some nearby ivy.
Yet it was only a few years ago – I think when came across discarded nests in the garden – that I released I have carried around with me since quite young the metaphor that a nest is a bird's home – it is where the bird family lives. Perhaps I made up that idea as a child. More likely I was told that or heard it on a children's programme. If so, perhaps it was not meant to be taken too literally – it was just meant to compare the nest with something that would be familiar to a child. But I think well into adulthood I had this notion of that birds lived in trees – not explicitly, but insidiously in the back of my mind: as if a bird had a home in a tree and that was where it was based – unless and until perhaps it could afford to move upmarket to a better tree!
They decided to do their own build, which involved Peter in the tiring work of going out to get building materials.
Peter set about the serious business of setting up their new dream home.
Peter was quite confident, and would often return which rather large pieces of nesting material.
"Oh, that seems to have got caught up."
Over time Peter started to be more realistic in selecting material he could get through the front door.
Although I was well aware (at one level) that birds do not have permanent family homes to which they return at the end of a hard day's exertions, I also had this nest=home identity at the 'back of my mind' giving the impression that this is how birds live. As humans we take for granted certain kinds of forms of life (perhaps home, work, family, etc.), and these act as default templates for understanding the world. This makes anthropomorphising nature seem quite a natural thing to do.
Peter heading out to work, again.
And getting home with his latest acquisition – landing on his feet.
Watching this process develop was quite entertaining. Peter would spend ages pecking at pieces of plant that were firmly fixed in the ground, ignoring nearby loose material. His early attempts to take material back to the nest were troubled. He would take material that was too large to get through the foliage into the secluded nesting area. He would also fly close to 'home' and then abort as found he could not land with his goods. However, he soon seemed to learn what worked, and developed a technique of first flying onto the fence or the roof the ivy was growing on to, so he would not be flying up to the nesting place from the ground in a single stage.
The sequences below show the pigeon flying out from, and back to, the nest.
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The jumping/diving action is clear in the sequence below:
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The fourth and fifth frames in the sequence below show the 'landing gear' coming into position (reminiscent of a bird of prey taking its prey):
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The landing action is also clear near the end of the sequence below:
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Another take off. catching the first few flaps:
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My favourite sequence – quite extended for my hand-held camera work! – in the 11th frame our pigeon is just entering frame right. But notice a sparrow sitting on top of the foliage to the left. The sparrow has presumably seen/heard the much larger bird comings it way, and in the next frame can be seen to be moving its wings ready to take off. The next three frames have the sparrow heading right as the pigeon moves to the left (the sparrow is a smudge beneath the pigeon's left wing in the third of these frames), and the sparrow appears to have disappeared from view in the next, but must have been obscured by the pigeon as it seen to the right of the next frame. The sequence ends with the pigeon in landing mode.
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 an atom which he identified as showing "electron configuration…of an element, sodium".
Focal figure shown to Brian
Brian identified the electrons and nucleus, and was asked about the arrangement of the electrons:
Can you tell me why the electrons stay there, in these positions, why they don't fly off into space?
'Cause they're held by the nucleus.
In what way does the nucleus hold them, any idea?
It's got a positive charge, and so attracts the electrons, which are negatively charged.
Okay, so, it's got an electrical attraction there.
Yeah.
Why don't they just go into the nucleus then, if they're attracted, why don't they just get pulled into the nucleus?
Because, 'cause there's more than one electron, they repel each other, and keep them out.
Ah, so what about these ones [on opposite sides of the nucleus] though, these repel each other do they, even though they
Yeah.
are drawn on opposite sides?
Yeah.
So that's what stops them actually falling into the nucleus, that they repel each other?
Yeah.
It seems that Brian recognised electrical interaction between the nucleus and the electrons in an atomic structure. He also recognised that electrons would repel each other, but did not seem to have considered that in itself that was an insufficient explanation for the structure of the atom (as, for example, the sole electron in a hydrogen atom does not fall into the nucleus).
Although Brian's explanation was based on sound principles (negative electrons repel each other), it is an alternative conception. Coulombic forces are proportional to charges and diminish with separation – inspection of the figure should suggest that the two inner electrons (tending to be pushed inwards by outer electrons) at least must experience net force towards the nucleus.
The stability of atoms – the failure of electrons to spiral into the nucleus leading to atoms collapsing – was one of the phenomena which led to the development of quantum theory. In classical physics the stability of electron orbits was a puzzle to be solved, as orbiting electrons 'should' have acted as electrical oscillators, and emitted energy as their orbits decayed into the nucleus whilst the atom (very quickly) collapsed. Quantum theory posited limited allowed energy states, rather than a continuum of possibilities – but learners new to the topic do not know about this.
