Alright. Let's clear that off and go to the next one. And let's just write
covalent formulas. And so once you've gone through and figured out how to go from the
formula to the name, going from the name from the formula is really easy. And so let's start
with this first one. This is dihydrogen monoxide. And so what's first? We have 2 hydrogens.
So I'm going to write H2. And then we have one oxygen. So that would be H2O. And so instead
of saying water, you can ask people if they could pass you a glass of dihydrogen monoxide.
And they'll tell you that you're a total geek. Let's go to the next one. Dinitrogen trisulfide.
That's going to be N2. And then we have S3. Because we have 3 of these sulfides. Let's
got to the next one. Silicon dihydride. That's going to be Si. And then we're going to have
H2. Or if we go down here, sulfur hexafluoride. That's just going to be SF6. And so covalent,
writing the formula is really easy when we're going from the name to the actual formula.
Okay. Let's go to the last one. And that's writing ionic formulas. Ionic formulas remember
are always written where you have the cation on this side and the anion on this side. So
let's go back. We've got lithium and oxide. Now when you're going from the name to the
actual formula of it, as far as ionic formulas go, it's a little more complex. Because you
have to make sure that it balances. And so we've got a lithium on this side and an oxide
on that side. We want to go find that on here. So lithium has a plus 1 charge. Oxide has
a 2 minus charge. And so when I write that out I have to balance that. And so this is
going to be Li. So lithium had a one charge. So I'm going to have to put 2 of those with
one oxygen. In other words I need to balance it out. Let's go to the next one. We've got
iron chloride. We know that iron has a 3 plus charge because this is iron (III). So we better
figure out what the charge of chloride is. So let's look back at our periodic table.
Chloride is going to be way over here. It has a minus 1 charge. So let's go to that.
So we've got a minus 1 charge on this side. And so we have to balance that out. So we
know it's going to be Fe. We don't write the Roman numeral. Because we only write that
in the name. And so how many of the chlorine atoms or chloride ions do we have to have?
It's going to be FeCl3, if you were thinking that. Let's go to the next one. Manganese
(IV) chromate. So that's going to have a 4 plus charge on the left side. And now we've
got to figure out what chromate actually is. And so let's go to the periodic table. So
chromate is going to be, let me find it on here. Chromate is going to be way up here.
So chromate is going to be CrO4. And that's 2 minus. So CrO4 and that's going to have
a 2 minus charge. And so let's go forward for a second. So this is right here going
to have a 2 minus charge on this side. And so how many of those do we have to have? Well
we're going to have two of the chromates. And so let's write manganese first. So that
going to be Mn. And now all of this whole polyatomic anion has a 2 minus charge. And
this is where the parenthesis come in handy. So I'm going to put a parenthesis around CrO4.
So this is CrO4 like that. And I have to have 2 of those to balance the charges. So I'm
going to put a two right down here. And so that's what that subscript outside the parenthesis
actually means. Let's go to the last one. Zinc. So if we find zinc on our periodic table,
zinc is going to be, it's way over here. So zinc has a 2 plus charge. And we're going
to combine that zinc with thiocyanate. And so this has a 2 plus charge. And now let's
find the thiocyanate. Thiocyanate is going to be way over here and that is SCN. And that
has a 1 minus charge. So let me go forward and figure out this last one. So this has
a 1 minus charge on this side. And so what I'm going to write for this, this is going
to be zinc. And so that is going to be, let me go back for a second, it's going to be
zinc which has a 2 plus charge. And then I'm going to put my thiocyanate, but I'm going
to have to have two of those because they have a 1 minus. So I'm going to put a SCN
and then I'm going to have to have two of those to balance out. So now we've gone from
writing the name to writing the formula. Now why do we have to balance all of these out?
As I clear this, remember all of the atoms on here want to be a noble gas. In other words
the noble gases have full outer valance shells. And so if you think of it like a tennis ball,
a tennis ball, if it had electrons around the outside of it, if you don't have eight
you're a very unstable tennis ball. And if we can either lose electrons and become a
cation we can become stable. Or we can gain one to get an outer shell that's stable, then
it's a happy atom. And so hydrogen has one electron. It would love to get two. And it
can share that with oxygen. That's why water ends up being H2O. And so that's how you name
things. Hopefully you can look at a can of Mountain Dew now and you can figure out what's
actually on it. And so I hope that was helpful.