Atoms and the Periodic Table


Mr. Andersen describes atomic structure and tours the periodic table.

Transcript Provided by YouTube:

00:04
Hi. This is Mr. Andersen and this is part two of atoms and elements. In
00:10
part one I talked about the history of the atom and how it came to be known as the atom.
00:16
In this one I’m going to talk about what do we have in here. So in here we’ve got these
00:20
things. We’re going to call those protons. We’ve got these things, and we’re going to
00:24
call those neutrons. And then out here we have this cloud of probability where we have
00:29
these things called electrons. And so this is more of a nuts and bolts. In other words
00:34
what do you learn from looking at the periodic table. So let’s get started. On the periodic
00:39
table you have essentially a box. And that box represents one atom. And so that represents
00:46
one type of element. And so we’ll call this neon right here. So neon is a gas. It’s a
00:50
noble gas. And if you put it inside a tube and run electricity through it, it’s going
00:54
to glow. But what do we know from this 10 and this 20 and this 2 and this 8. What does
00:59
that tell us? And so essentially what we’re looking at is a periodic table is organized
01:04
according to its atomic number. So the atomic number is going to tell us the number of protons
01:10
that we have. Okay. What else does the atomic number tell us? It also tells us the number
01:15
of electrons that an element has. Because the positive charges of the proton and the
01:20
negative charges of the electrons will always equal each other out. The next thing we have
01:24
is the mass number. So the mass number, the mass of an electron is really really small.
01:29
It doesn’t weigh much. And so the mass number tells us the mass or the number of protons
01:35
we have plus the number of neutrons that we have. Okay. So what are protons? Those are
01:42
positive charges. What are neutrons? They weigh the same as protons but they have a
01:46
neutral charge. And then what are electrons? Electrons are going to have a negative charge.
01:50
But again they’re going to move around the outside. And so let’s kind of do one of these.
01:54
And I’m going to use the Bohr Model right now. And so this is not really what an atom
01:58
looks like, but we’ll get more specific a little bit later. And so let’s start in the
02:02
middle. So this is going to be the nucleus right here. So if we look at this up here,
02:05
neon, the 10 at the top, so that’s how the periodic table is organized, the 10 at the
02:10
top is going to tell us how many protons it has. And so let’s say if it has 10 positive
02:16
charges on the inside. Next one. This is the average atomic mass. And so if you’re going
02:21
to solve one of these they have to tell you what the mass number is. But let’s say the
02:24
mass number, for example, of neon is 20. What does that mean? Well there’s 10 protons and
02:30
there’s also going to be 10 neutrons. And so on the inside we’re going to say that there
02:34
are 10 neutrons on the inside. Because the number of protons and the number of neutrons
02:39
always add up to the mass number. Okay. Now let’s figure out the number of electrons.
02:44
Well there’s something that you should remember. And I’m going to write this up at the top.
02:47
And that is 2, 8, and 8 and 18 and it keeps going like this, but for now let’s just remember
02:58
that. 2, 8, 8 and 18. In other words the electrons always go in specific energy levels. Okay.
03:05
So let’s go back to it again. So we’ve got 10 protons in here. So how many electrons
03:09
do we have? Well we have 10 electrons. Because remember the charge is going to be the same.
03:14
But those electrons always fill their way up from the inside to the outside. So what
03:17
does that mean? We’re going to have 2 electrons in this first energy level like that. Okay.
03:25
So we’ve taken care of 2. And now we only have eight electrons left to take care of.
03:30
Well, how many can I put in the next level? This is why I said you really want to remember
03:34
this up at the top. Well I can put 8 electrons in the next level. And so I’m going to say
03:37
we’ve got 8 electrons in the next level. Now we’ll learn in later chapters, it’s kind of
03:43
wavy, that electrons are happy if this energy level is filled. Or atoms are happy if it’s
03:49
filled. And so since this is 8 electrons on the outside, this is a really happy kind of
03:54
an atom. And neon exists just by itself because it’s got that full energy level right there.
04:00
Okay. So that’s a lot of stuff. Let’s see what we can remember. Let’s do something like
04:04
nitrogen. Okay. Nitrogen makes up most of what you’re breathing right now. So let’s
04:08
go through it again. So if you look at it, our atomic number is 7. So how many protons
04:13
does it have? 7 protons. How many neutrons does it have? Well let’s round this for a
04:19
second. Because this is the average. And so let’s say that it’s 14. So if that’s fourteen
04:23
as a mass number, that means we have 7 neutrons. Alright, so let’s go around the outside. So
04:28
let’s say that this is our nucleus. Now let’s do electrons. Well there are 7 electrons.
04:32
And so you’re going to put two electrons in the first level. We’re going to put them like
04:36
that. So we draw this first energy level. And so I’ve taken care of two of those. And
04:42
so now we have 5. And so how many are in the next level? It’s going to be 5 electrons in
04:47
the next level. So it looks like that. This is kind of sloppy. But there’s 5 electron
04:53
in there. And now you’re starting to see why we have these number a lot of the time on
04:56
a periodic table as well. So what does nitrogen want? Well nitrogen would love to have 8 electrons
05:02
in this next level. And so it only has 5. And so if it could gain those electrons somewhere
05:07
else, so this is something that is really important. This is called ammonia. And ammonia
05:12
is NH3. And so that’s 1 nitrogen atom and 3 hydrogens. And so eventually in the next
05:18
few chapters we’ll start talking about chemical bonds. And so what hydrogen can actually offer
05:22
to nitrogen is those three electrons it can share. And so you should be able to do that
05:26
with any kind of atom on the periodic table. But let’s look at the periodic table then.
05:30
How is the periodic table actually organized? If you look at it our atomic number here is
05:35
going to be 1. And then it goes all the way, let me change to a different color that you
05:40
can actually see. It goes over here to 2. And then it’s going to go back over here to
05:44
3. And then 4, 5, 6, 7, 8, 9, 10. Okay. So the periodic table is ordered according to
05:51
its atomic number, the number of protons. But now you should start to see why we had
05:56
to remember that 2, 8, 8, 18. If you look across the top, we’ve got two elements in
06:08
the first level. We’ve got eight in the next level. We’ve got eight in the next level.
06:15
And then we’ve got eighteen as we come all the way across like that. Now why is it that
06:19
we have those numbers? Well again, it’s quantum theory which is pretty confusing. So we don’t
06:23
really have to understand why yet. We just have to know that it exists. Let’s kind of
06:27
walk through this in your head for a second. Let’s start with hydrogen. Hydrogen is 1 on
06:32
the atomic number. So it’s going to have 1 periodic, excuse, it’s going to have 1 electron
06:38
in its outer level. But let’s look at another one. So let’s look at for example lithium.
06:44
How many electrons does it have in its outer level or sometimes we call that its valence
06:50
level or valence electron. So we look at lithium. Well lithium is going to have 2 electrons
06:56
in the first level. And it’s going to have 1 electron in the next level. And so that’s
07:00
odd. So hydrogen and lithium both have 1 electron in the outer level. Well it’s not that odd
07:05
because if we look at the next ones, sodium, how many does it have in the next level? Well
07:09
it’s going to have, sodium is going to have 2 electrons in the first level. It’s going
07:14
to have 8 electrons in the next level. And it’s going to have 1 electron in the outer
07:17
level. And so the number of electrons you have on the outside of an atom really determines
07:21
how an atom behaves. And if you think about it, in the periodic table, all of these atoms
07:26
or all of these elements are going to have 1 valence electron or 1 electron in the outer
07:30
level. And so they’re going to share properties. And so these are called the alkali metals.
07:35
And they’re metals that are highly reactive. One of my favorite Myth Busters is when they
07:39
keep trying to throw all these alkali metals into a toilet and seeing them react with water.
07:46
So you get explosions. If we look way over here on the other side, these are going to
07:49
be the nobel gases. Nobel gases are this group right here, are all going to have filled outer
07:55
levels. And so they’re really, they’re really stable. Or if you look at these ones right
08:00
here, these ones are actually called the halogens. Halogens are all going to have 7 electrons
08:05
in their outer level. And why is life made out of carbon? It’s because carbon has 4 electrons
08:11
in it’s outer level. And why is water H2O? Ooops. Let me try that again. Water is H2O
08:19
because oxygen which is right here is going to have 6 valence electrons. But it can grab
08:24
two of those electrons from hydrogen to make H2O. And so how is the periodic table organized?
08:30
It’s organized according to the number of protons in ascending level. But more importantly,
08:36
it’s the verticality that tells us a lot. Every time you go up and down in the periodic
08:41
table you’re going to have elements that have the same number of valence electrons. And
08:44
so you see cool relationships like this. Copper, silver, gold. They’re all in the same column
08:49
and that’s because they have really similar properties. Just like carbon and silicon right
08:54
on top of each other. They all have 4 valence electrons. And so they kind of have the same
08:59
properties. They’re really good at forming bonds. And so that’s what an atom looks like.
09:03
And that’s basically how the periodic table is organized. But we’re going to spend way
09:06
more time getting into the nuts and bolts of that and drawing some Lewis dot diagrams
09:10
a little bit later. But I hope that’s a good start. Thanks.


This post was previously published on YouTube.

Photo credit: Screenshot from video.

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