What Does An Atom REALLY Look Like?
https://www.youtube.com/watch?v=EOHYT5q5lhQ
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. Don’t forget to subscribe if you want to keep up with us. 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.
No comments:
Post a Comment