Hi. This is Mr. Andersen and this is part two of atoms and elements. In
part one I talked about the history of the atom and how it came to be known as the atom.
In this one I'm going to talk about what do we have in here. So in here we've got these
things. We're going to call those protons. We've got these things, and we're going to
call those neutrons. And then out here we have this cloud of probability where we have
these things called electrons. And so this is more of a nuts and bolts. In other words
what do you learn from looking at the periodic table. So let's get started. On the periodic
table you have essentially a box. And that box represents one atom. And so that represents
one type of element. And so we'll call this neon right here. So neon is a gas. It's a
noble gas. And if you put it inside a tube and run electricity through it, it's going
to glow. But what do we know from this 10 and this 20 and this 2 and this 8. What does
that tell us? And so essentially what we're looking at is a periodic table is organized
according to its atomic number. So the atomic number is going to tell us the number of protons
that we have. Okay. What else does the atomic number tell us? It also tells us the number
of electrons that an element has. Because the positive charges of the proton and the
negative charges of the electrons will always equal each other out. The next thing we have
is the mass number. So the mass number, the mass of an electron is really really small.
It doesn't weigh much. And so the mass number tells us the mass or the number of protons
we have plus the number of neutrons that we have. Okay. So what are protons? Those are
positive charges. What are neutrons? They weigh the same as protons but they have a
neutral charge. And then what are electrons? Electrons are going to have a negative charge.
But again they're going to move around the outside. And so let's kind of do one of these.
And I'm going to use the Bohr Model right now. And so this is not really what an atom
looks like, but we'll get more specific a little bit later. And so let's start in the
middle. So this is going to be the nucleus right here. So if we look at this up here,
neon, the 10 at the top, so that's how the periodic table is organized, the 10 at the
top is going to tell us how many protons it has. And so let's say if it has 10 positive
charges on the inside. Next one. This is the average atomic mass. And so if you're going
to solve one of these they have to tell you what the mass number is. But let's say the
mass number, for example, of neon is 20. What does that mean? Well there's 10 protons and
there's also going to be 10 neutrons. And so on the inside we're going to say that there
are 10 neutrons on the inside. Because the number of protons and the number of neutrons
always add up to the mass number. Okay. Now let's figure out the number of electrons.
Well there's something that you should remember. And I'm going to write this up at the top.
And that is 2, 8, and 8 and 18 and it keeps going like this, but for now let's just remember
that. 2, 8, 8 and 18. In other words the electrons always go in specific energy levels. Okay.
So let's go back to it again. So we've got 10 protons in here. So how many electrons
do we have? Well we have 10 electrons. Because remember the charge is going to be the same.
But those electrons always fill their way up from the inside to the outside. So what
does that mean? We're going to have 2 electrons in this first energy level like that. Okay.
So we've taken care of 2. And now we only have eight electrons left to take care of.
Well, how many can I put in the next level? This is why I said you really want to remember
this up at the top. Well I can put 8 electrons in the next level. And so I'm going to say
we've got 8 electrons in the next level. Now we'll learn in later chapters, it's kind of
wavy, that electrons are happy if this energy level is filled. Or atoms are happy if it's
filled. And so since this is 8 electrons on the outside, this is a really happy kind of
an atom. And neon exists just by itself because it's got that full energy level right there.
Okay. So that's a lot of stuff. Let's see what we can remember. Let's do something like
nitrogen. Okay. Nitrogen makes up most of what you're breathing right now. So let's
go through it again. So if you look at it, our atomic number is 7. So how many protons
does it have? 7 protons. How many neutrons does it have? Well let's round this for a
second. Because this is the average. And so let's say that it's 14. So if that's fourteen
as a mass number, that means we have 7 neutrons. Alright, so let's go around the outside. So
let's say that this is our nucleus. Now let's do electrons. Well there are 7 electrons.
And so you're going to put two electrons in the first level. We're going to put them like
that. So we draw this first energy level. And so I've taken care of two of those. And
so now we have 5. And so how many are in the next level? It's going to be 5 electrons in
the next level. So it looks like that. This is kind of sloppy. But there's 5 electron
in there. And now you're starting to see why we have these number a lot of the time on
a periodic table as well. So what does nitrogen want? Well nitrogen would love to have 8 electrons
in this next level. And so it only has 5. And so if it could gain those electrons somewhere
else, so this is something that is really important. This is called ammonia. And ammonia
is NH3. And so that's 1 nitrogen atom and 3 hydrogens. And so eventually in the next
few chapters we'll start talking about chemical bonds. And so what hydrogen can actually offer
to nitrogen is those three electrons it can share. And so you should be able to do that
with any kind of atom on the periodic table. But let's look at the periodic table then.
How is the periodic table actually organized? If you look at it our atomic number here is
going to be 1. And then it goes all the way, let me change to a different color that you
can actually see. It goes over here to 2. And then it's going to go back over here to
3. And then 4, 5, 6, 7, 8, 9, 10. Okay. So the periodic table is ordered according to
its atomic number, the number of protons. But now you should start to see why we had
to remember that 2, 8, 8, 18. If you look across the top, we've got two elements in
the first level. We've got eight in the next level. We've got eight in the next level.
And then we've got eighteen as we come all the way across like that. Now why is it that
we have those numbers? Well again, it's quantum theory which is pretty confusing. So we don't
really have to understand why yet. We just have to know that it exists. Let's kind of
walk through this in your head for a second. Let's start with hydrogen. Hydrogen is 1 on
the atomic number. So it's going to have 1 periodic, excuse, it's going to have 1 electron
in its outer level. But let's look at another one. So let's look at for example lithium.
How many electrons does it have in its outer level or sometimes we call that its valence
level or valence electron. So we look at lithium. Well lithium is going to have 2 electrons
in the first level. And it's going to have 1 electron in the next level. And so that's
odd. So hydrogen and lithium both have 1 electron in the outer level. Well it's not that odd
because if we look at the next ones, sodium, how many does it have in the next level? Well
it's going to have, sodium is going to have 2 electrons in the first level. It's going
to have 8 electrons in the next level. And it's going to have 1 electron in the outer
level. And so the number of electrons you have on the outside of an atom really determines
how an atom behaves. And if you think about it, in the periodic table, all of these atoms
or all of these elements are going to have 1 valence electron or 1 electron in the outer
level. And so they're going to share properties. And so these are called the alkali metals.
And they're metals that are highly reactive. One of my favorite Myth Busters is when they
keep trying to throw all these alkali metals into a toilet and seeing them react with water.
So you get explosions. If we look way over here on the other side, these are going to
be the nobel gases. Nobel gases are this group right here, are all going to have filled outer
levels. And so they're really, they're really stable. Or if you look at these ones right
here, these ones are actually called the halogens. Halogens are all going to have 7 electrons
in their outer level. And why is life made out of carbon? It's because carbon has 4 electrons
in it's outer level. And why is water H2O? Ooops. Let me try that again. Water is H2O
because oxygen which is right here is going to have 6 valence electrons. But it can grab
two of those electrons from hydrogen to make H2O. And so how is the periodic table organized?
It's organized according to the number of protons in ascending level. But more importantly,
it's the verticality that tells us a lot. Every time you go up and down in the periodic
table you're going to have elements that have the same number of valence electrons. And
so you see cool relationships like this. Copper, silver, gold. They're all in the same column
and that's because they have really similar properties. Just like carbon and silicon right
on top of each other. They all have 4 valence electrons. And so they kind of have the same
properties. They're really good at forming bonds. And so that's what an atom looks like.
And that's basically how the periodic table is organized. But we're going to spend way
more time getting into the nuts and bolts of that and drawing some Lewis dot diagrams
a little bit later. But I hope that's a good start. Thanks.