Thomson's Plum Pudding Model of the Atom

So the word atom means uncuttable, so the Greeks were thinking of it as a tiny hard sphere.

Phil: That's right.

Derek: And even up until the eighteen hundreds, that was the idea of an atom, the smallest piece of matter, a tiny hard sphere. But then we find out that that's not quite right, not quite. There were experiments in the eighteen hundreds that discovered the electron. JJ Thomson's experiments really worked out the electron was smaller than an atom, about 1000 times smaller than a hydrogen atom, and it was in all atoms.

Phil: That's right, not just hydrogen.

Derek: Whatever material he did his experiments on, he found there were electrons in them. There are electrons in all atoms. So I guess when you find something smaller than an atom, you need to propose a new model for the atom that actually has something smaller in it, some substructure.

Phil: That's right. So something like this. This is our model of the atom.

Phil: This is our model of the atom - in his day, it was known as the plum pudding model, but uh... here we have cherry tart.

Phil: Cherry tart, ok. So the idea being that we have an overall atom, usually pictured as spherical rather than 2D, but uh... but imbedded within it – and this is the important part – there are negative electrons represented by cherries, and they can come out. The overall atom is neutral, so that means that pudding part must be positive.

Derek: Now how would you get one of these electrons out of our pudding here? So electrons are negatively charged, so we'll need to put something very positive, which attracts electrons – a high voltage.

Derek: And that would have the effect of, say, like plucking a cherry out of the pudding.

Phil: That's pretty much it, yeah. You could do it kind of like that, so we're simulating what it would be like to put a positive charge up here.

Phil: That's right, that's right.

Derek: Pulling the electrons out of the atom, that's quite delicious.

Phil: Yeah! Well, that is the most delicious model of the atom, I've gotta say. So shall we uh, split the atom? Why don't you go ahead?

Phil: You want me to do it?

Derek: Yes! Who knows what could happen; a whole bunch of energy could be released.

Phil: Yeah, one, two, three...