Bill was a year 7 student who participated in the Understanding Science project. He told me that previously when in primary science "we did a lot about plants, and – inside them, how they produce their own food". As he had been talking to me about learning about particles (e.g. Gas particles try to spread out and move apart), I asked if there was any link between these two topics.
Okay. What about particles, we were just talking about particles, do you think that’s got anything to do with particles?
Well in the plant, there is particles.
Are there?
’cause it’s a solid.
Ah. So there’ll be particles in that then?
Yeah.
Is it all solid, do you think?
Inside the stem is, ‘cause going up the stem there would be water, so that’s a liquid. And, it also uses oxygen, which is a gas, to make its food, so. I think so.
So it would be solids, liquids and gases?
Mm, I think some.
But they’ve all got some particle in them, they are all made up of particles.
Yeah.
Okay.
As Bill had talked to me earlier about ther being particles in a gas when ice was melted, and then boiled, I wanted to see if he though the particles in different substances were the same:
Erm. Do you think that the particles in the, oxygen’s a gas isn’t it?
Yeah.
Do you think the particles in the oxygen gas, are the same as the particles in the steam that you said was a gas, in your experiment you did earlier?
Erm, I don’t think so, no.
You think they’d be different sort of particles?
Yeah, they’re different gases.
Okay. And in the solid part of the plant, do you think the particles that make up the solid part of the plant, are the same as the particles that make up this table, that’s a solid?
Well, the particles, plants are soft, some plants are soft, and you, when you squeeze them they’re, they feel soft and erm, but the table is hard so I think that the particles would be slightly different, but they would have, because they hold this different shape, and they would, they would be {pause} erm {pause} then they would, ob¬, then they would be softer as well.
So the softer, the plant which is softer,
Yeah.
would have softer particles?
I think so yeah
And the harder wood, made of harder particles?
I think so.
That’s interesting, okay.
Here Bill offered evidence of a very common alternative conception about the particle theory. A key feature of particle theory is that chemists use particle models to explain the properties of substances macroscopically (what can be observed directly) in terms of the very different nature and properties of conjectured 'particles' (quanticles) at a submicroscopic level. Yet aftre learning about these 'particles', students commonly 'explain' macroscopic properties of substances and materials by suggesting that the particles of which they are made up themselves have the property to be explained - being hard, sharp, colourless, conducting, etc.*
* An article that discusses this alternative conception ( Building the structural concepts of chemistry: some considerations from educational research) can be found in the open-access journal, Chemistry Education Research and Practice. The article can be accessed either by signing in through an Institutional login (e.g. for Universities) or through a personal login that anyone can obtain by registering with the journal for free.
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Dr Keith S Taber kst24@cam.ac.uk
University of Cambridge Faculty of Education
© Keith S Taber, 2012