>> Welcome to Adams and Elements Part Two B. This video lecture
will focus on valence electrons and the Octet rule.
Let's get started.
Now elements with the same number of valence electrons,
and remember, that means outer most occur
in the same column, ok?
And a name of a column is the group.
Alright? So this makes a really handy when we're looking
at the periodic table,
the number of valence electrons is simply equal
to the group number for a column.
Now they've updated the periodic table and so this really works
for the roman numerals with the newest edition you have to look
for the number in the one's place.
And so it's a little hard to see here, let's yeah,
we'll just go with it.
You have your periodic table; so for example here where it says
like group thirteen, right, it's the three is in the ones place,
so this group would have three valence electrons, right?
So anytime we look at the top
of the periodic table we have the group number.
We know how many valence electrons there are.
Now what we're going to learn
about in more detail today is the valence electrons
on metals are lost to empty their valence shell to get back
to having the Octet, right?
And so when we lose electrons, right,
remember electrons are negative, so if we lose electrons,
we're forming cations, which are positive.
Now non-metals, they gain valence electrons
to fill the valence shell right?
So we're going to add electrons to create octet, right?
And so gaining electrons we form anions,
which are negative, alright.
So here is right, so if you don't,
if the periodic table doesn't have it,
we just add it with our minds eye.
This stair step line creates the partition and we'll like,
loop around here a little bit right, so everything
to the left is metal and everything
to the right is a non-metal.
Alright, now here hydrogen, hydrogen is very interesting.
We typically show hydrogen here, alright, but it is a non-metal,
so you can also think of hydrogen living over here.
Alright, it's one of the only elements
that can be both a cation and anion.
So any time we look
at the periodic table we see this stare step line
and we recognize all the elements to the left are metals
and the elements to the right are non-metals
and then we can take what we've learned, right,
that this is the alkali metals right plus one alkaline earth
plus two; there's our buddy aluminum, right,
plus three right, loses those three valence electrons;
carbon for our, for our course we're not going to worry
about ion's forming there.
Let's move over here to the non-metals, right?
So here is group seventeen or group seven;
so there's seven valence electrons, right?
So we just add one, let me we just need
to add one that's why it's a minus one.
There's our halogens, oxygen, oxide and sulfide
and then nitrite and phosphate.
Right, now in the middle here, right,
here are those tricky transition metals;
they have variable positive charge, alright.
So we can see that ion formation is driven
by the number of valence electrons.
So let's make sure
that everybody feels confident with this.
Let's work a few practice problems.
Ok, so if we look here, for example, right, calcium,
here's our calcium, right, so it has two valence electrons
and if you've already memorized it, right, we know that, oops,
I don't know why I did that right, calcium two plus.
Right and then there's our buddy aluminum right there,
so it has a three valence electrons, so it's plus three.
And I think sometimes the anions are a little trickier so,
but here we've already practiced, here's oxygen,
so we'll circle that right here right
so that's group six or sixteen, right.
So we do the one, so there's six valence electrons, right.
So we need to add two for octet.
Let's, ok, so that's why oxide is minus two and then last
but not least, here's bromide, right, group seven or seventeen;
so it has seven valence electrons, so it only needs one
for form the octet, right.
So the metals and the non -metals gain
and lose electrons to create the octet.
Let's look a little more closely at this.
So we can see now how the chemical properties are
determined by the number of valence electrons.
So that's the octet rule; atoms gain, lose or share electrons
to create full valence shells.
Alright and that's where we get our octet, ok.
And so we're going to focus for this series on gaining
and losing, right, so that's our ionic compounds and then
on our next class section we'll look at prevalent compounds
and how they share electrons.
Alright, and so we can see that the of type,
the compounds types are determined by the type
of chemical bound and that's the attractive force
that holds you know, two or more atoms together in a compound.
So let's put this all together right.
So ionic compounds are always going to have a cation
and an anion, right and there, so for example we could have,
let's look, right, so here's magnesium fluoride, right.
Magnesium, group two, alkaline on earth, it has a plus two
and so that's why we need two fluorides to balance the charge
and then this is the schematic of an ionic compound.
I think they're a little trickier to visualize
because they're little magnetic balls.
They're attracted together;
there's this electro static attraction, right?
There's no visible bond to see.
We just have to imagine it; just image it just like the positive
and negative poles of magnetics would be attracted
to each other, the positive and negative charges are attracted.
Alright, with covalent compounds, right,
oh so that would be here, right, so this was electronic exchange
and they shut their electron transfer right on it,
lost and gain for covalent, it's electron sharing.
Alright, and so that's the covalent bond
and so we'll just do a very simple, alright,
we'll just do a hydrogen H2, of the hydrogen the, right,
there we go, so here are our two shared electrons.
>> Right and so covalent compounds
like I mentioned we'll get to later, but we're just kind
of seeing how the rules come into play
and let's summarize now.
Alright, so this stare step line is a really big deal
because ionic compounds are going to have the metal
and the non-metals
where covalent compounds are only going
to have two non-metals.
So remember the first thing we want to do when we look
at a compound is look at the elements in play
and see whether we have metals in non-metals or two non-metals.
Right, we have electron transfer here, so we're going
to have cations and anions with full charge.
Here we have electron sharing because their, the cations
and anions can come together in a variety,
if you look at like salt, right, we have little crystals of salt
or big crystals of salt, those are ionic compounds.
There's no discreet molecule, so we call these salts,
right or we talk about the crystal lattice
and they can vary in size.
Oops there we go, ok, but a molecule,
a molecule has a beginning and an end;
it has a fixed size, right?
So there's an introduction to valence electrons
and how we can use our understanding of them
to just discern between ionic and covalent compounds and then
on this page here, let's look and practice this
to make sure we're comfortable applying this knowledge,
alright.
So first off, right, when we look at the periodic table,
pay attention to that stare stepped line, alright?
See the number of valence electrons at the top
of each group; remember that hydrogen can, is a non-metal;
so you want to see it in both places.
And as we come up, so well you'll just have to look
at your periodic table.
I won't be able to show you to whole thing.
Right, so if we look here we see calcium, it's a metal
and bromide, is a non-metal; so this is an ionic compound.
When we look at this next one, right, carbon,
well let's see we can, right, there's carbon and hydrogen
and oxygen; so all non-metals that makes it covalent, alright.
And then last but not least, here's our buddy sodium,
which we know is an alkali metal and sulfide,
so we have sodium plus one; so we're going to need two of those
and then we have our buddy sulfide, so we have our,
once again our metal and our non-metal;
so we know it's ionic.
Alrighty, so that concludes our introduction
to valence electrons and the octet rule.
Now would be a good time to work a couple post video
practice problems.