Keith S. Taber
Amy was a participant in the Understanding Science Project. When I talked to her near the start of her GCSE 'triple science' course in Y10 she told me that ionic bonding was "atoms which have either lost or gained electrons so they are either positively or negatively charged" and that chemical bonding was "like in a compound, where two or more elements are joined together", but she seemed unsure how the two concepts were related.
I followed up on Amy's use of the term 'compound' to explore how she understood the term:
How would you define a compound?
Erm …Something which has erm two or more elements chemically bonded.
… So you give me an example of that, compound?
Erm, sodium oxide.
Sodium oxide, okay, so there are two or more elements chemically bonded in sodium oxide are there?
Uh hm
And what would those two or more elements be?
Sodium and oxygen.
Okay. Erm, so when we say sodium oxide is chemically bonded, what we are saying there is?
[pause, c 2s]
Erm – a sodium atom has been bonded with a oxygen atom to form erm a new substance.
So Amy's example of a compound was sodium oxide, which would normally be considered essentially an ionic compound, that is a compound with ionic bonding. So this gave me an opportunity to test out whether Amy saw the bonding in sodium chloride and sodium oxide as similar.
Okay, so that was chemical bonding,Mm.
and that occurs with compounds?
Yeah.
And what did you say about ionic bonding?
Erm, it's the outer electrons they are transferred from one element to another.
Now what does that occur in? You gave me one example, didn't you?
Uh huh
Sodium chloride?
Yeah
…Erm. Would sodium chloride be er an element?
[pause, c.2s]
Sodium chloride, no.
No?
It would be a compound.
You think that would be a compound?
Yeah.
And a compound is two or more elements joined together by chemical bonding?
Yeah.
So Amy had told me that sodium chloride, which had ionic bonding, was (like sodium oxide) a compound, and she had already told me that a compound comprised of "two or more elements chemically bonded", so it should be follow that sodium chloride (which had ionic bonding) had chemical bonding.
Do you think sodium chloride has chemical bonding?
Er – I think so
And it also has ionic bonding, or is that the same thing?
Erm,
[pause, c.2s]
I dunno, I've never thought about it that way, erm,
[pause c.3s]
I'm not sure, erm
[pause, c.2s]
I dunno, it might be.
Clearly, whatever Amy had been taught (and interviewing students reveals they often only recall partial and distorted versions of what was presented in class) she had learnt
- (1) that ionic bonding was transfer of electrons (an alternative conception) as in the example of sodium transferring an electron to chlorine; and that
- (2) a compounds was where two or more elements chemically bonded together, and an example was sodium oxide where the elements sodium and oxygen were chemical bonded.
Yet these two pieces of learning seemed to have been acquired as isolated ideas without any attempt to link them. Initially Amy seemed to feel ionic bonding and chemical bonding were quite separate concepts.
When taken through an argument that led to her telling me that sodium chloride, that she thought had ionic bonding, was a compound, which therefore had chemical bonding, there should have been a logical imperative to see that ionic bonding was chemical bonding (actually, a kind of chemical bonding – as the logic did not imply that chemical bonding was necessarily ionic bonding). Despite the implied syllogism:
- sodium chloride has ionic bonding
- sodium chloride is a compound
- compounds have elements chemically bonded together
- therefore ionic bonding …
Amy was unsure what to deduce, presumably because she had seen the two concepts of ionic bonding and chemical bonding as discrete notions and had had given no thought to a possible relationship between them. However explicit teaching had been on this point, it is very likely that the teacher had expected students to appreciate that ionic bonding was a type of chemical bonding – but Amy had not integrated these ideas into a connected conceptual structure (i.e., there was a learning bug that could be called a fragmentation learning impediment).
