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 gendral experience, and inappropriately applied in the context of atomic interactions.
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Dr Keith S Taber kst24@cam.ac.uk
University of Cambridge Faculty of Education
© Keith S Taber, 2012