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. She was shown a representation of a benzene molecule, with a circle inside the hexagon (a convention intended to symbolise the aromatic nature of the compound, due to the delocalisation in the pi-system around the carbon ring). Annie suggested a different meaning for the symbol:
Now do you know what compound that is? Any idea?
(pause, c.3s)
Looks like a benzene ring.
Yeah, that’s right. Any idea what this, er, strange looking circle in the middle is? Or what it’s meant to represent?
Shows where the electrons are, because it’s electron rich.
Electron rich, so that shows where the electrons are. So all the, where, all the electrons are what? In the middle of the circle, or what?
(pause, c.6s)
Yeah, sort of they’re denser in the circle.
They’re denser in the circle, so,
Yeah,
in here there’s a lot of electrons are there?
Yeah.
So right in the centre of the picture, in the middle of the circle we’ve got a lot of electrons. Are, is it all of the electrons in the molecule are in there?
No.
No?
Just the, just the ones from the carbons.
Just the ones from the carbons.
Yeah.
Okay, so why do you say it’s electron rich, what does that mean exactly?
Erm, not really sure, but I wrote it down yesterday.
(Both laugh)
We use a lot of conventional symbols in science, and often once we are familiar with them we tend to take their meaning for granted. Yet in teaching we need to regularly revisit and reiterate these conventions as they may not be obvious to students, who may, like Annie, look to interpret the symbols in ways that make sense to them.
Later in the interview, there was an opportunity to check that Annie did not appreciate the nature of delocalisation in the benzene system:
…this is the one, you said it was benzene, didn’t you? …And we decided, did we, that these were single bonds,
Yes.
but they’re also covalent bonds.
Yes.
But there’s no double bonds.
No.
Return to ECLIPSE homepage
List of science topics
Dr Keith S Taber kst24@cam.ac.uk
University of Cambridge Faculty of Education
© Keith S Taber, 2012