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.
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.
