Hi. This is Mr. Andersen and today I'm going to be talking about atoms
and elements. This here is a picture of helium. And if we look at helium right here, you know
that this is the nucleus here in the center. To give you an idea of scale the nucleus,
which is going to be the tiny bit down here is actually measured in fentometers. So that
is 10 to the negative 15th meters. In other words this is really small. The angstrom unit
here. But atoms are incredibly small. And so in this podcast what I'm going to talk
about is the history of atoms, how it came to be known that there exists an atom and
then finally we'll talk about what are protons, neutrons, electrons. And then how are they
organized. Okay. So let's start a little bit with history. And so when we get into the
modern day science, I love this guy. This right here is Mendeleev. And so what Mendeleev,
a Russian scientist, was doing is he took playing cards and we would put information
about each of the known atoms that we have. So maybe the atomic mass, and properties of
it. He'd write that on the playing cards. And then he just laid them out on a table.
And what he finally figured out is that you put them in a certain areas or certain order
according to their atomic number. And kind of what we had was the modern day periodic
table came out of that. If you really want to waste some time, this is a wonderful website
to go to. This is periodictable.com. This was developed by a person by the name of Theodore
Gray. I think he also started mathematica. But the cool thing about it is that you can
click on certain things. So this carbon for example and what you can get are these wonderful,
he's collected all these different atoms, excuse me all these different elements. And
he has real world examples of it and then a bunch of properties of that as well. And
so you could waste a lot of time looking at that. And I have an app for this on my iPad
that is just really really cool. And so I love this picture here, because it shows you
all the different things. And what you find on here is that there's all these relationships.
So if we look for example right here, copper, silver and gold are all organized at the same
point on here. And so as you start to play around with the periodic table you find all
this cool stuff. So let's go back in time a little bit. And so if we go through the
important people in the history of the atom, in my class I don't think it's super important
that you memorize all of these, but it is important to give us a little bit of context.
And so let's first start with this guy. His name is Democritus. And he was greek and so
what he essentially did is said, imagine if we take everything and then we divide everything
in half. So let's say a block of wood. And then we divide it in half again. And we divide
it in half again, divide it in half again, divide it in half again, divide it in half
again, divide it in half again, divide it in half again. If we just kept doing that
over and over and over again, we eventually get something that's really, really small.
And that really small thing he called atomos. And that just means, atomos I think that's
right, undivisible. In other words we can't break it down anymore. And so he's the first
guy to come up with this idea of atoms. But he wasn't a scientist. So then we fast forward
a little bit and this here is, quite a bit actually, this right here is John Dalton.
And John Dalton was doing studies. So he was measuring the mass of things. And he came
up with our modern atomic theory. And so the modern atomic theory is this. He knew that
hydrogen for example, there would be two hydrogens for every one, let's see, one oxygen. And
so he thought they were hooked together. They were like the little hooks in them that would
hook those together. And he knew that you were going to have two hydrogen for every
one oxygen that you're going to have. There was a specific ratio. But that first theory
is that elements are made up of specific atoms and they come together in a certain ratio
to make a compound. So that sounds a lot like what we think of today. How's that different
from our modern theory? Dalton thought they were just these round balls. So they weren't
made up of a different things. And so let's go forward a little bit. So who's up next?
This guy right here. His name is JJ Thomson. And JJ Thomson discovered the electron. Let
me show you how he did that. He used something called a cathode ray tube. So a cathode ray
tube looks like this. You essentially have gas and then you run electricity through it.
And what you get is a ray that goes right through the middle of it like that. Now we
have things in our house, like a CRT, like your television, most of the televisions that
we have are a cathode ray tube. It's a little bit different than the new tvs that we have
today. But essentially what JJ Thomson found is if you held a magnet up here, so if we
put a magnet right here, what it did is it bent the cathode ray. So it bent that ray
of electrons. And so he used magnets and he also used electric fields. And what he found
is that since we're pushing that, when there is a like charge, he discovered, I think he
called them corpuscles or something like that. But we call this today the electron. So he
discovered the electron. What else did he come up with? Well he came up with what we
call the plum pudding. In other words he thought that atoms, instead of just being that ball
that Dalton believed is that you had a positive charge inside it. But then you had all these
negative charges inside here as well. So you had negative electrons that were kind of embedded
in this positive ball. Okay. So let's go forward a little bit. And tweak that. So this is Ernest
Rutherford. Ernest Rutherford is famous for his gold foil experiment. And essentially
what he did is took a bit of gold, so this is gold foil. And then he shot alpha particles
out of it. And so alpha particles were shooting out through here and they would travel through
the gold. He had a little sensor on this side that would sense where the alpha particles
go. Now what is an alpha particle? Alpha particle is essentially like the, it's two protons
and two neutrons. And so it's the nucleus of a helium. And so what happened is as these
alpha particles came shooting through, some of them would kind of be turned to the side.
But occasionally one of these alpha particles would come shooting right back. And when it
came shooting right back it kind of freaked out Rutherford. And Rutherford said it was
like shooting a giant shell. Or a bullet at a piece of tissue paper and occasionally one
of those bullets comes flying back at you. So what did he discovered was the nucleus.
And he knew that it had a positive charge because those positive alpha particles were
being shot back. So he discovered the nucleus. And so let's go to the Rutherford model. Rutherford
model said that we had a positive charge in the middle and then we had these negative
electrons going around the outside. And so they went kind of zipping around the outside
like that. And he had realized that most of that space on the inside was that. It was
mostly just space with a tiny little nucleus. Because just a few of those alpha particles
actually came shooting back out. Alright. Let's go next. Next, this is Niels Bohr. Niels
Bohr, let's circle him down here, Niels Bohr is Danish. He works in Rutherford's lab. And
the problem with Rutherford's lab is that they discovered this positive charge on the
inside and this idea that you have electrons going around the outside. But physics predicts
that if you have a negative charge here and a positive charge out here, that quickly that
negative charge is going to be attracted to it and so the whole Rutherford model didn't
really work. And so what did Bohr figure out? Bohr figured out that we've got this positive
charge on the inside. We've got electrons going around the outside. But they go in specific
orbits around the outside. So those electrons were not traveling here, but they had to travel
in this specific orbit. And so that's the Bohr model. That you got a positive nucleus
and then electrons going around the outside in specific obits. Okay. Let's go next. Next
we get into the weird world of quantum physics. And so this right here is a man by the name
of Schrodinger. Schrodinger is famous for Schrodinger's cat, if you've ever heard of
that. And so what Schrodinger said is that electrons aren't particles. That they're actually
waves. And so there's this duality. And so now we had this kind of competition between
those people like Bohr who said electrons are particles. Schrodinger said it was more
like a wave. And so we had to sort out this. And so we eventually get to Heisenberg. But
first we've got this guy. Chadwick. And what Chadwick discovers is the neutron. It's weird
but it took us way longer to discover the neutron. That's because it has no charge.
But it accounted for that mass. And then finally we have his guy. This is Werner Heisenberg.
And why Heisenberg figured out is that both Rutherford, excuse me. Both Bohr and Schrodinger
were right. In other words what does an atom look like? It's got a positive charge which
we now know neutrons on the inside. But there's kind of this wave of probability out here.
And so is an electron a particle? Yeah. But it's described by Schrodinger's idea of a
wave. So we got pretty deep. But what is this? This is this quantum theory that we have today.
It describes how electrons move.