Hi. It's Paul Andersen and this is chemistry essentials video 6. It's on periodicity.
In other words it's going to be the patterns that we see in the periodic table. Now what
determines that is going to be electron configuration. And we can figure that out using the aufbau
principle. Which is actually German and it means principle of building up. So we're building
up from lower to higher energy levels. And so what we can find is these trends that start
to emerge. But it's most important instead of just memorizing them that you really understand
what's going on inside the atom that determines those trends. And so periodicity remember
is going to be derived from the electron configuration. In other words where the electrons are. We
can determine that by using the aufbau principle. And if you were to watch the last video on
electron configuration I think that would help a lot. But what's the meaning behind
this? It all comes from Coulomb's Law which helps to explain electron configuration. And
also helps to explain these trends that explains changes in the ionization energy. Changes
in the atomic and ionic radii. How big the atom or ion is. Electronegativity. And finally
the ion charge. And so if you really understand Coulomb's Law you can kind of work your way
through this on the periodic table. Why is this important? We can use the periodic table
to make predictions, especially about things that we haven't even designed yet. And so
if we look at the periodic table, this on the right side is going to show us which of
these are going to be filled over time. But if you look at the periodic table, we'll find
trends. And so here's hydrogen. What we really need to do is take helium and then put it
over in this s block. It's going to make us, it's a little easier to understand. And so
what we're going to have are energy shells and then these would be subshells within that.
And so one thing you should understand about the periodic table is that this f block should
slide right in here. It would be hard to write a convenient periodic table, but that's really
how it should be set up. Generally we've just put it down below. And so what's guiding this
or explaining the electron configuration, remember, is Coulomb's Law. And so it's pretty
simple. If we look at the protons on the inside of the nucleus they have a positive charge.
The electrons have a negative charge. And so Coulomb's Law says we just multiply those.
In other words, the bigger they are, the bigger the force between the two is going to be.
But as we increase the radius, the distance between the nucleus and those electrons, then
we're going to see a decrease in that force. The one thing that you have to add to that
is that once we fill up one of these orbitals or subshells, it's going to shield the electrons
on the outside from those on the inside. So let's get started and work through this list.
What's going to happen to they ionization energy? Well let's look at Coulomb's Law.
Ionization energy is the energy required to pull one of these electrons away. And so what's
going to happen as we increase the size of atoms we're going to increase the number of
protons. And so we're going to make it harder for you to pull an electron away. And so we
move across the periodic table. We're going to see an increase in ionization energy. What's
going to happen as we go down the periodic table? Well as we go down the periodic table
they're getting bigger and bigger and bigger. And so the radius is going to get larger.
And so therefore we're going to see a decrease in ionization energy. So you can think of
ionization energy going up and to the right. Now it's not as simple as this. What we're
really looking at is within subshells we're going to see that pattern. Because you'll
see changes within here and orbitals as well. But it's just a general trend. And it comes
from Coulomb's Law. Let's look at atomic and ionic radii. Well what happens as we increase
the atomic number? We're increasing the number of protons. What is that going to do? It's
going to pull it in. In other words it's going to pull those electrons more closely to the
center. And so it's actually going to be the opposite. Or it's going to increase as we
go down. And it's going to increase as we go from the right to the left across the periodic
table. And so you can see this graph of atomic radii is actually going to be the inverse
of what we saw with ionization energy. What about electronegativity? Electronegativity
is how much an electron, and it's bad to say this, but wants an electron. In other words,
how much it would like to receive another electron. Well remember as we're going across
a subshell, let's say we're going across this p block right here, as we go across we're
increasing the number of protons. And therefore we're increasing that pull of the nucleus
on the electrons outside it. And so as we move from the left to the right, we're going
to increase how much that atom wants an electron, at least until we get to the noble gases.
And so electronegativity is going to follow ionization energy as well. What if we look
at then ionic charge. Well to look at ionic charge we really have to look at how close
an atom is to a noble gas. And so let's throw a noble gases up here. Noble gases are going
to have a full inner electron subshell. And so anything that moves you towards that is
going to make you a more stable atom. And so remember the only atoms that exist by themselves
are going to be the noble gases up here. So a quick way to figure out ionic charge using
Coulomb's Law is to just look how close you are to a noble gas. And so let's look at the
halogens which are right here. How many electrons would halogens have to get in order for them
to move to a noble gas? Well just one electron. And so they're going to have in general a
negative one charge. Let's move over. These would have negative two, negative three. Let's
go way to the other side with the alkali metals. What about them? Well it would hard to go
all the way across here to get to the noble gases. It's just easier to go around the back.
In other words they could loss the electron. And when you loose the electron you have a
positive one charge. And so we could kind of work it up in this direction as well. And
so again, it's not holdfast. In other words, these are general trends. But they can all
be predicted just by applying Coulomb's Law. So it's hard to talk about the periodic table
without talking about Dmitri Mendeleev, who's really the father of the periodic table. But
you've probably never heard of Julius von Meyer, who was a German working on the periodic
table at the same time and published his periodic table around the same time as Mendeleev. Now
why haven't you heard of Meyer? Well Mendeleev made these huge predictions. In other words,
here's his periodic table. And you see here that he had some question marks, where they
hadn't identified those atoms. What he did was he would predict them. And so he predicted
germanium and he called it ekasilicon. And here all of the predictions he made about
the properties of this ekasilicon. And if we look at his predictions and then compare
it to the actual values all the way down, you'll find that he was pretty much spot on.
And that's why Mendeleev is given credit for the periodic table. Not only was he able to
build it, put it together. But he also made these great predictions. And his predictions
were spot on. And so that kind of lends to this next topic I want to talk about which
is material design. What we can do is we can take things off the periodic table. So let
me grab some atoms. Let me grab some silicon and some oxygen. And so we make some silicon
dioxide. And when we do that we get a ceramic. A ceramic is going to be built up, maybe stoneware
or earthenware. So it's going to build up these tiles over here on the side. And so
if silicon dioxide can make that, well what about something below that. What about tin.
What if I grab that? I could say maybe those are going to form ceramics. And they will.
They'll form glazes that are going to be on these ceramic tiles as well. And so what scientists
can do is they can dance around the periodic table. And if you know some of these trends
you can make predictions about new materials. And so again in summary, periodicity comes
from the electron configuration which is determined by the aufbau principle. But what really explains
it is Coulomb's Law which allows us to make these big predictions. Ionization remember
goes up and to the right. Atomic radii increases down and to the left. Electronegativity up
and to the right. And then ionic charge remember we find where the noble gases are and then
we look at how many electron we have to gain or lose to get there. And then these are important
in designing materials. So you should have learned to predict or justify trends in atomic
properties. Where would I point you if you didn't get that? Remember looking at this
chart and seeing how ionization and electronegativity change. If we were to look at justifying the
arrangement based on reactivity, it all goes back to Coulomb's Law. And remember the bigger
the charges the are, the bigger the ionization energy or the bigger the force holding the
electrons in place is going to be. There's also this shielding effect. And then remember
we can identify patterns to predict design. And the example of silicon and tin oxides
are an example of that. So that's periodicity. And I hope that was helpful.