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More is different

by Michael Nielsen on August 12, 2005

What’s the difference between neon and ammonia?

In its most common isotope, a single neon molecule (one atom, in fact) contains 10 neutrons, 10 electrons, and 10 protons. A single ammonia molecule also contains 10 neutrons, 10 electrons, and 10 protons. It’s the same stuff! I think this is very cool.

Update: Well, I can’t count. Ammonia only has 7 neutrons. I know this kind of phenomenon is possible, because I set it as a problem once in a mini-course I gave on metals and superconductors, and people came back with several solutions. Unfortunately, I don’t remember what they were.

Update II: Potassium Bromide (K Br) and Calcium Selenide (Ca Se) appear to do the trick, assuming no more silly mistakes. Can anyone find a simpler example?

Update III: Helium and Deuterium both have 2 protons, 2 neutrons, and 2 electrons. It’d still be nice to have examples involving two more familiar substances.

Update IV: Commenter Kurt points out a better example: Nitrous Oxide (laughing gas) and Carbon Dioxide, both with 22 electrons, protons, and neutrons. Any better? I think salt and nickel 58 (the most common isotope) also provide an example.

From → General

4 Comments
  1. Kurt permalink

    Well, let’s not forget about good old water, or methane, while we’re at it. (Does that pattern carry on further up the periodic table?) And imagine the complexity of trying to figure out from first principles that there would be these different stable configurations for 10 neutrons, electrons and protons, and that the barrier between them would be high enough to keep water and methane from spontaneously collapsing into neon (or at least, not very often)?

    Kind of makes one’s head spin. Gee, things couldn’t have turned out this way by chance, must be the work of some intelligent designer…

  2. Kurt permalink

    Ugh, can I withdraw my earlier comment? In my defense, I was lead astray by Michael’s numbers!

    Okay, as an attempt to redeem myself, how about carbon dioxide and nitrous oxide? I think those both have 22 each of protons, neutrons and electrons.

  3. >Update III: Helium and Deuterium both have 2 protons, 2 neutrons, and 2 electrons. It’d still be >nice to have examples involving two more familiar substances.

    Erm, Michael, Deuterium has 1 proton, 1 neutron and 1 electron. The Deuterium molecule, D_2 (or more correctly ^2H_2 ) has two of each. At STP, this is Deuterium gas.

  4. I was referring to the molecule. I thought of stating that explicitly, but thought it’d be pretty obvious, for exactly the reason you describe.

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