Electrons & Protons


bohr-modelI remember asking my high school chemistry teacher why the curriculum covered Bohr’s solar-system-like model of the atom that we’re all so familiar with but never ventured into the more accurate quantum model.

Our conversation went something like this… “Quantum mechanics is too complicated, it will only confuse students.”

To which I replied, “How do you know that? How do you know you’re not confusing them by not teaching a more accurate model? Perhaps the Bohr model is inadvertently misrepresenting the situation and making it more difficult than it ought to be.”

He countered with, “It’s too hard to picture electrons as a wave and probabilities collapsing into a particle.”

“Like rain condensing from a cloud?” I replied, “Or drops of water forming on a window when it’s foggy outside?”

And that’s the thing about quantum mechanics, sure it’s difficult to understand, but it’s made even harder by the insistence that it is too difficult. Instead of giving up on public understanding, we should be looking at ways to make this remarkable field of science easier to grasp.

Have you ever played with a slinky spring? Or have you held a skipping rope with a friend and shook it up and down to form a standing wave? If so, you have a practical understanding of what waves are and how they perpetuate, and that’s a good place to start when considering subatomic particles.

Standing_wave_on_a_slinky

Atoms are made up of electrons, protons and neutrons.

In the simplistic Bohr model, -ve electrons orbit the +ve protons and neutrons in the nucleus, but the obvious question that arises is, why don’t these negative electrons spinning around positive protons collide and form lots and lots of neutrons? In other words, why to electrons and protons exist at all? Why haven’t they collided to cancel each other out and form neutrons?

It’s a good question, because according to classical physics, electrons should collide with protons to form neutrons. That they don’t was a significant clue that lead to our modern understanding of quantum mechanics.

I put this question to a friend of mine, scientist and fellow science fiction writer, Brian Wells. Here’s his response…

There are two answers to this question.

PARTICLE ANSWER:

It’s the electron/proton pair merging to form a neutron that is the culprit. At least when thought of in “particle form.” You’d think that, just like gravity, attractive charge would make two objects collide under circumstances that should be fairly common (like when they’re heading right for one another). However, when gravity makes things collide, you end up with exactly the same mass/energy you started with (if Earth is struck by an asteroid you end up with Earth plus the asteroid).

But when a proton and electron collide, they don’t form a neutron because neutrons are a bit heavier than the proton and electron you started out with. So for a proton and electron to collide and “stick,” there has to be energy added and converted into mass in order to form the resultant neutron. And even at the levels we’re talking about, that’s a LOT of energy.

Earth + asteroid === asteroid mushed into Earth
Proton + electron =/= neutron (as a neutron is more than simply a proton & electron stuck together)

When neutrons decay, which they do all the time when not bound in a nucleus, they don’t simply form a proton and an electron, they form a proton and and electron and a whole bunch of energy.

Ah, but we also have the electron’s added relativistic mass to work with, right? So how much mass does the electron need to add in order to have the necessary heft to form a neutron with a proton? Alas, it turns out that an electron must increase its mass by 250%, which is unlikely under any circumstance.

Of course, this raises the question: are the electrons colliding with the nucleus and just bouncing off because they have neither the mass nor the energy to form a neutron with the proton they’re colliding with? Or is something else at play?

Okay, short answer: something else is probably at play. Get ready for it… wait for it… wait…

stone-arch-swiss-river

WAVEFORM ANSWER:

It seems electrons in the inner shell form a charge around the nucleus that prevents electrons (even from within the inner shell) from reaching the nucleus. It’s like a stone arch — every stone wants to fall to the ground, but the pressure of the surrounding stones prevents any of them from falling.

But what about a simple hydrogen atom, you ask? How can you have an arch made of just one stone? Again, quantum mechanics. In wave form, the single electron forms a quantum probability cloud around a hydrogen nucleus, thereby suspending itself, effectively causing the single orbiting electron to interfere with itself and prevent itself from falling, just as a single photon of light interferes with itself in a double-slit experiment. It’s a case of strange, but true.

And scientists have just this week imaged the single electron “orbiting” a hydrogen atom. As the theory predicts, the electron exists as a wave surrounding the nucleus.

orbital-590x330

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7 thoughts on “Electrons & Protons

  1. Oh, that’s cool.One of the advantages of going to Chem engineering college is that I learn a bunch of advanced chemistry, including a little of what you told.I do agree that the general idea of quantum mechanics when applied to a problem like this one should taught more often. But, the whole concept is impossible to pass on because requires a lot of mental models that a lay person doesn’t have (a lot of math too), making the subject a couple of steps away in terms of inferential distance. It’s a fascinating topic, indeed. Sent from my BlackBerry 10.

    • Paulo, yeah, the maths and the models are not what we’d ordinarily expect based on what we see in the macro-world, which can make it a little mind bending, and yet it’s important to understand at least the broad concepts. I really like Brian’s analogy with the stone arch, where every section wants to collapse and that keeps the whole from collapsing, as it helps to grasp what’s going on at that level.

  2. In one of the articles you linked, it mentions that the electron “passes through” the atom’s nucleus. While language like this is common and, in the context of quantum mechanics, isn’t wrong, it’s more accurate to say that there is a non-zero probability that the electron can be found inside the atom’s nucleus at any given time. However, while it’s fun to note that such probabilities are non-zero (there’s also a non-zero probability that the electron can be found on the other side of the universe), that doesn’t mean we expect to observe such improbable things happen often, if ever.

    It’s like trying on new bowling shoes after playing peek-a-boo with a crocodile. Wait, is that even a metaphor? I dunno, I’ll read it again after I’ve had my coffee.

    Cowabunga. (Wait, is “cowabunga” a metaphor?)

    • Yeah, I did wonder about that… and that’s part of the challenge when it comes to QM, the concept is so abstract it’s difficult to know quite how accurate various articles are.

  3. Pingback: Introduction To Quantum No Jargons | Ramani's blog

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