Hey Crazies.
I’m here to burst your bubble again.
This picture of the atom is wrong.
The real atom is far weirder than we could have ever imagined.
So weird, that we had to rule out everything else before we could accept it.
And, judging from the length of the video, you can see we’re going to take our time
with this.
Alright, we can’t really understand where we are, until we see where we’ve been.
To the timeline!
Debates about atoms have been going on since Ancient Greece.
Democritus first suggested that matter was made of tiny invisible bits.
He called them “atomos” because he thought they were “indivisible.”
This is why we call them “atoms” today.
Of course, Aristotle thought it was a stupid idea.
I still do!
Why did I make you?
Anyway, the debate raged on for over 2 thousand years.
Finally, the 20th century was fast approaching and we made some headway.
Thomson discovered the electron in 1897 and proposed a simple atom in 1904.
Negative electrons floating in a positive mist.
Rutherford proposed a better one in 1911 with an atomic nucleus, but he wouldn’t discover
the proton until 1919.
Unfortunately, that nucleus couldn’t be made of just protons. That wouldn’t predict
the masses on the Periodic Table.
We had to wait until 1932 for the discovery of the neutron to explain it.
Neutral particles are really hard to find.
Alright, what do we know so far?
Negative electrons are on the outside surrounding a positive nucleus.
That nucleus is made of protons and neutrons, but, by the time we even knew about neutrons,
we already knew electrons didn’t orbit like this.
This picture is wrong.
So what does it really look like?
Well, it looks like this, but that’s probably not what you were hoping for.
Isn’t there, like, a visual model or something?
Like this, but more accurate?
Ok, I’ll give it a shot, but be prepared to have your mind blown.
Things got really weird in the 1920s, so let’s try to keep this as concrete as possible.
You are all seeing me because light is emitted by your screens.
We saw in a previous video that individual atoms can emit light too.
It’s called an emission spectrum and it can tell us what kind of atom it is.
Whatever model we come up with for the atom must explain that.
Let’s start with the most obvious question: How do atoms emit light?
Energy levels!!
Say we have hydrogen gas in a closed glass tube.
If we run a bunch of electricity through it, the electrons will absorb some of the electrical
energy.
When those same electrons fall back down, the energy gets emitted as light.
Slight problem though!
If that electron could jump to any energy, it could emit any color of light, but we know
it only emits these four colors: one red, one blue-green, and two violets.
The only possible conclusion: The electron can’t have any energy it wants.
It can only have very specific energies called “energy levels” and jumps between those
levels emit or absorb very specific colors of light.
We number these levels: 1, 2, 3, 4, 5, etc.; all the way to infinity.
The electron isn’t allowed to be anywhere in-between them.
Not even for a moment while it jumps.
It must disappear from one and reappear on the other.
I know, crazy, right?!
Anyway, back to hydrogen.
The four jumps for hydrogen’s visible spectrum are: 3-to-2, 4-to-2, 5-to-2, and 6-to-2.
Any other jump emits light that isn’t visible.
But why though?
That’s the question that takes us straight into madness.
When a measurement can only have certain values, we say it’s “quantized” and the light
emitted or absorbed during a jump between those values is called a “quantum.”
That’s right!
We’re talking about quantum mechanics!
We know that when things orbit by gravity, they can have any energy they’d like.
“Classical mechanics” is the mechanism for how that works.
Electrons don’t seem to obey those rules though.
So we needed a “quantum mechanics,” a mechanism for quantum particles.
Back to the timeline!
In 1924, a French physicist named Louis de Broglie proposed an idea.
What if electrons had wave properties?
The electron can only exist in certain energy levels because there must be a whole number
of wavelengths present.
They’re not actually orbits at all!
This was some serious out-of-the-box thinking, but it solved a couple of problems:
One!
Why can electrons only be in certain energy levels?
Cutting a wavelength up would be like cutting an electron up. Ridiculous!
A jump from one level to another is just a gain or loss of whole electron wavelengths.
Two!
Accelerating charges must emit light.
Why don’t electron orbits collapse?
An orbit is accelerated motion.
Electrons should continuously lose energy to light and fall into the nucleus.
But they don’t.
Why not?
They’re not actually orbiting.
They’re just waves.
But, if a wave like light, can come in little packets like a particle and little packets
like electrons can look like waves.
Why stop at electrons?
In 1926, an Austrian physicist named Erwin Schrödinger ran with that thought.
If all particles are also waves, then we’re going to need a wave equation to predict their
behavior.
Maxwell’s equations gave us something like this for light so that’s that kind of thing
we want for ALL particles.
Using the total energy of a particle, what we call the Hamiltonian, we get something
that looks like this, which is designed to help us figure out this: the wave function,
an equation to contain all the wave properties of a particle.
Another slight problem though!
Even if we think of the electron itself as waving in space a wave is still accelerated
motion.
It should still be continuously emitting light and collapsing into the nucleus.
The only solution is that the electron isn’t waving.
Wait wait.
Didn’t you just say it was waving?
Well, yes and no.
Ok I think it’s time for a summary again.
The nucleus is made of protons and neutrons and there is a cloud of electrons surrounding it.
The behavior of all those particles is governed by wave functions.
But, if the particles themselves aren’t doing the waving, what is waving?
Later in 1926, a German physicist named Max Born butted into the conversation and suggested
maybe, just maybe, it’s a wave of probability.
I know, I know.
It’s nuts!
But it fixes all the problems.
I think Richard Feynman put it best when he said:
The wave function for an electron in an atom does not describe a smeared-out electron with
a smooth charge density.
The electron is either here, or there, or somewhere else, but wherever it is, it is
a point charge.
Huh?
Alright, here’s how it works:
Even though a particle itself isn’t a wave, its properties are.
Where it is, what it’s doing, how much energy it has; all these things are wave-shaped,
but they’re only waves of probability.
Say the position of an electron looks like this.
It’s not smeared out across all space.
It just doesn’t have a definite position.
It’s most likely to be here, but also pretty likely to be here or here and it’s probably
not going to be any of these places.
But it could be almost anywhere!
So what happens if I try to measure where it is?
It’ll only be one place.
You just can’t predict where that will be.
The act of measuring it, changes what the wave looks like.
It changes the wave from this to this but even then it’s not exactly known.
There’s still a little wiggle room.
That’s what the uncertainty principle is all about.
But the measurement doesn’t destroy the wave.
It just collapses it to a simpler shape.
Luckily, some measurements can be made together.
The energy, the magnitude of angular momentum and at least part of its orientation can all
be measured together, so those are allowed to be definite all at the same time.
Again though, there’s still a little spread.
A little wiggle room, which is what gives emission lines their thickness.
But the definiteness of these measurements gives us a lot of information about electrons
in atoms.
Information we use to categorize them into shells and orbitals.
Ok final summary.
The nucleus is made of protons and neutrons and there is a cloud of electrons surrounding it.
The behavior of all those particles is governed by wave functions.
But those are waves of probability, so everything is at least a little bit vague.
We’re not sure exactly what anything is doing or exactly where it is, but we can make
some great educated guesses.
And that’s enough to predict the entire periodic table.
So got any questions?
Please ask in the comments.
Thanks for liking and sharing this video.
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And until next time, remember, it’s ok to be a little crazy.
We tried out a new type of video and everyone seemed to love it.
But Jeremiah Pendley asked if it would take away from my other content.
That’s a solid “no” Jeremiah.
I just don’t want to do the same thing all the time.
I need variety, so I’m mixing into the line-up.