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## Why your kids’ model of the atom is completely wrong

When I was in elementary school, at some indeterminate age, I made a model of the atom with pipe cleaners and Styrofoam balls.  It probably looked something like this:

These models are about as accurate as depicting the Taj Mahal as a decrepit hovel:

The Taj Mahal, built from 1632–1653.

Sure, the atom has a nucleus; this nucleus has protons and (usually) neutrons.  And electrons “orbit” the atom (although quantum mechanics tells us that this “orbit” is a much more nebulous concept than Bohr would have us believe).  But—and here’s the main problem with 5th grade Styrofoam ball models—the scale is completely, totally, massively wrong.

Let’s do a simple calculation.  A typical atomic radius is one the order of 0.1 nm.  A typical nucleus, about 10 fm.  What is the ratio of these two lengths?

This bears repeating.  A nucleus is something like 10,000 times smaller than an atom, by length.  By volume, it’s even more dramatic:

A nucleus is 1,000,000,000,000 times smaller than an atom, by volume.

You don’t really get that impression from the Styrofoam ball model, do you?

A typical football stadium has a radius of maybe 120 m.  One ten-thousandth of this is 1.2 cm, about the size of a pea.  To get a sense of what an atom really looks like,  place a pea at the center of a field in the middle of a football stadium.  Then imagine, at the outskirts of the stadium, there are a few no-see-um gnats (biting midges, of the family Ceratopogonidae).  These bugs represent the electrons.  The atoms are the bugs and the pea.  That’s it.  The rest of the atom is empty space.

Another way to think about it is this:

In terms of volume, a nucleus is only 0.0000000001% of the volume of the atom.

That means, for those of you scoring at home, that 99.9999999999% of an atom is nothing.

That is, you are mostly nothing.  So am I.  So is Matt Damon.

So the next time you’d like to help your kids make a model of the atom, just forget it.  Whatever model you make will be about as accurate as the physics in The Core.  I’d recommend instead getting some nice casu marzu, having a strong red wine, and watching True Grit.  You’ll thank me for it.

There’s flies in this, too.

### 2 Responses

1. I often wonder what Leucippus and Democritus (the first Greek Atomists) would have said if they were ever told just how small an atom is, and that’s its mostly nothing but open space.

To be sure, if I ever come upon a time machine these two historical giants are getting a visit from me 🙂

2. As a Physics teacher I could not agree more. The nucleons are no more bonded together than the guests at a party are and they move around within the nucleus just as freely. And the electrons most certainly do not move around the nucleus in circular orbits. There are none of these things hanging in my Physics lab.

They do serve to start the discussion about what a model really is and what it does (explains particular aspects of an object) and these models explain chemical bonding well. It’s just a pity that too few teachers know how to lead the discussion.

Thanks for a valuable contribution to Science.