Tag: submicrosopic level

Electrons would contain some of the element

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.

Understanding Chemical Bonding project – Focal figure 3

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).

Annie went on to suggest that carbon electrons would be bigger than chlorine electrons.

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.

Quantile ontology

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