Edward was a participant in the Understanding Chemical Bonding project. he was interviewed at the end of the first year of his A level chemistry course. He was asked about an electron orbiting the nucleus of a hydrogen atom that he thought would "move within a spherical…area".
If you had your hydrogen atom, and the electron was happily moving round in this spherical, erm, orbital or whatever, and suddenly the proton were removed by magic - which obviously couldn’t happen - but if it were, would the electron continue to move as it did before?
No. They’d be no force acting on it.
So, would it be at rest?
It would remain at rest.
It would suddenly come to a halt?
(pause, c.3s)
No it wouldn’t. On taking the neutron (proton) away, the speed that it has, ignoring frictional forces, it would continue to maintain.
Right, do you think it is fair to, to ignore frictional forces? - We’re talking about an electron moving around an orbital in a hydrogen atom.
(pause, c.8s)
Well it’s got a very small mass, so I don’t think it would effect it that, that much.
So Edward, a student studying Advanced Level chemistry and physics seemed to think an electron would be influenced by friction, although not greatly because of its small size. The notion of friction is applicable at the familiar macroscopic scale, but is not meaningful at the submicroscopic scale of individual atoms, ions and molecules.
What is a frictional force?
Air resistance, or erm, friction between, a body and a plane.
Right, do you think the electron, in a hydrogen atom, undergoes air resistance?
Yes.
This was a surprising response, as Edward should have realised there could not be any air (a mixture of gases, composed of molecules) inside an atom, although younger children have often been found to talk of air between the atoms or molecules making up a material.
Yeah? - How does it do that? What, what exactly - if you could see a sort of erm, a picture of it undergoing this air resistance, what would it look like?
Mm, that’s a difficult one that. Erm.
(pause, c.3s)
Thinking about it, if it’s a hydrogen atom, then nothing can exist between that electron and the nucleus, because air molecules are made of atoms and you can’t have an atom in a hydrogen molecule.
So would it experience air resistance?
No, it wouldn’t.
At this point Edward had reasoned himself to the scientific perspective. It seems Edward understood the molecular realm well enough to realise that concepts like air resistance do not apply, but had initially not thought things through, and presumably simply applied an assumption that frictional forces are ubiquitous so would apply to any situation we was questioned about.
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Dr Keith S Taber kst24@cam.ac.uk
University of Cambridge Faculty of Education
© Keith S Taber, 2013