Hi. It's Mr. Andersen and this is chemistry essentials video 8. It's on atomic
models. What is a model? A model is essentially a theoretical construct. And so it exists
in our brain and we use it to explain how phenomena works. And so phenomena, let's say
gravity for example, is almost like a black box. We don't get to touch it, but we get
to essentially develop models that help to predict it. So let me find a scientist that's
a little brighter than me. And how would Albert Einstein look at gravity? Well what he was
doing, he was looking at the constructs, the models already developed by Sir Isaac Newton.
But then he as able to improve on that based on data that he had received. So why does
an apple fall to earth? It's not that there's some magical force pulling it there. What
Einstein said is that they're both warping space time and these objects are traveling
the closest path. And so light would travel along the same path. And he was able to confirm
that using data. And so if we look at the atom, the atom is very similar. Atoms are
so small. I think in a human body we have 10 to the 14th cells. And then if we were
to look inside the cells we have 10 to the 14th atoms in every cell. And so it's incomprehensible
how small atoms are and how many of them we have. And so we can use data to predict what
an atom looks like. So the Dalton model that there were just these spheres that would connect
was a model. As we discovered the nucleus we came up with the Rutherford model. And
then we used spectra to come up the Bohr model. And then quantum physics gave us more of this
quantum mechanical model developed by Erwin Schrodinger. And so we're improving this theoretical
construct of what an atom is like. And so we've got an atom, which is phenomena. And
then we have an atomic model which is just a construct of what we think that looks like.
And what we're able to do is gather data from the phenomena. And as long as that fits our
model then everything is good. But once we start to conflict with that model then we
have to develop a new atomic model. And we play that against the data. As long as everything
fits we use that model. But if it doesn't then we develop a new atomic model. And that's
really how science works. And so an example, if we're looking at the atom. The atom, they
used to, once they discovered the nucleus and the electrons, this was our model. It's
our theoretical construct of what an atom was like. But once the data didn't fit, once
we got spectral data that said that these electrons aren't just moving everywhere, that
they're confined to orbits, then we came up with the Bohr model. And that worked until
we started to look at ionization energy. Learn more about quantum mechanics. And then we
developed the model that we have today. And so as long as that works, as long as it fits
the data, that's the model that we're going to use. And so let's look at that one transition.
How did we go from this Bohr model to more of a quantum mechanical model? Well let's
look at ionization energy. Remember ionization energy is the amount energy it takes to pull
an electron away. And so if this is our model, you've got 2 electrons in the first shell.
Then we'd go 8 in the next shell. And then we move out like that. Ionization energy should
be like this. Hydrogen to helium. That works great. That would be the first subshell. But
it should be really smooth as we move all the way from lithium to neon. But it simply
isn't. And so we had to develop a new model. And that model consists of shells and now
subshells. And then those subshells are further divided into orbitals. In other words why
would the ionization increase and then drop down again? It's because of the shielding
effect of this 2s orbital. And why would it change here? It has to do with electron-electron
repulsion. And so again, a model is simply a theoretical construct. And what we can do
is as long as the data fits, we'll use it. But once the data changes we have to adopt
a new model. And so what you should have learned is how to determine that evidence is consistent
with the model. And so I would point you back to this. The data coming in from ionization
energy didn't fit the model, that Bohr model that we had. So we had to modify it. And we'll
probably modify our current model in the future as well. And it will give us a better and
better and better understanding of an atom and what an atom is like. But I hope that
was helpful.