WEBVTT
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molecular formulas are a way for us to represent molecules
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using a chemical formula. So you know what the
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molecule is made up of. So, for example
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, um, water is a molecule that can be
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represented by the chemical formula H 20 because it consists
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of one oxygen bonded to two questions. So the
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thing about molecular formulas are that it is useful when
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you want to figure out how maney atoms make up
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the molecule, but it doesn't give information about how
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the molecule is bonded. So, for example,
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let's say that you have something like this. So
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again, going back to my isomerization example, let's
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say you have a chain of four carbons, and
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it actually does not exist in nature. Um,
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it actually has Hudgens bonded to it. But for
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the sake of this example, um, I did
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not, including Hudgens eso We'll just be focusing on
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the important part, which is the carbon chain of
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the molecule. So let's say you have and China
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four carbons. The chemical formula, um, for
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the structure is C 48 10 so you can have
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the same chemical formula for this molecule, but for
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a different structure. So again going back to my
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Asama realization example from before. You can also have
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this kind of structure, and it will still have
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the chemical formula. So it's important to note that
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although chemical formulas are useful, it will not give
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you any information about bonding s so that we can
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go into a few practice problems that you might see
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regarding molecular formulas. Eso, for example, you
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can be given a name of something, and you
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will be expected to write the chemical formula for it
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. So for my first example, let's say then
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you need to write the chemical formula for ammonium chloride
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. So first we need to figure out, um
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, what each word means in terms of its Adams
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and then figure out the appropriate molecular formula. So
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ammonia is an island that is Polly Atomic. And
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so this is actually NH four. Plus, we
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know that chloride is an an ion specifically in Israel
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as the chlorine atom with a negative one charge.
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So if we were to write a chemical formula for
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this, it would be a nature. Four c
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. L where the canyon is written on the left
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side and the chloride is Britain after the, um
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, carry on and so you can see that this
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is a molecular formula because the overall charge of the
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species is neutral. So it is important to make
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sure that when you're given thes two different ions for
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the name, you make sure that the overall charge
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is neutral. So let's do another example. Eso
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. Let's say you want to write a chemical formula
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or sodium carbonate again. You want to make sure
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that you know what each component is. So then
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you can write a chemical formula, and so the
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stadium is any plus. And carbonate is also a
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poly atomic and Alan Um, which has a charge
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of two months. So here this is a bit
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different from the first example, because our Canton has
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the same attitude of charge as our enemy. But
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now we have a sodium with a plus one charge
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in a carbonate with a minus two charge. So
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if you want to write a chemical formula, you
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want to have to sodium ions instead of one and
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just one carbonate, and this is because any has
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a charge of plus one, and carbonate has a
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charge of minus two, so To balance this,
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we need another sodium atom to make sure this species
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is mutual. So here we see that sodium carbonate
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means any to C 03 And so for another example
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, let's say you want to write the chemical formula
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floor aluminum oxide. So whenever you see oxide in
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your chemical name, this usually alludes to oxygen,
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which is an anti on with a charge of two
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minus and using the same method as before. You
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want to make sure that you know what each component
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means before writing out the molecular formula. So aluminum
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has a three plus charge and referring back to the
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previous videos. We know that based on the position
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of aluminum, we can predict that alumina will create
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a three plus cat on and in the same case
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for sodium, according to the group's. We can
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predict that sodium makes a Plus one church and stay
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with oxide as well in the case that in its
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specific group it creates a charge of T minus.
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So if we were to write a chemical formula for
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aluminum oxide, you would first try to figure out
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how to do this while creating a neutral atom So
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we know that Luna has a plus three charge and
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oxygen has a to minus charge. And so,
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um, to make sure these air bound out,
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we can use a common factor of six. So
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then we can have two aluminum's and three oxygen's.
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So then we can write. This has ailed 203
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So this would be our chemical formula because it includes
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both the aluminum component and the oxide component. And
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when you add these two things together and um,
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consider the charges of each ion, we can create
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a neutrally charged species, which is this final molecule
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. And for our last example, let's say you
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want to create a chemical formula for aluminum sulfate.
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So again you want to follow the same procedure.
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So we know that aluminum has a plus three charge
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, and sulfate is a poly atomic and ion,
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and it actually has a charge of minus two.
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So using the same methods as before, we want
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to make sure that our molecule is neutral at the
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very end. So we need some number of aluminum
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in some number of this Polly Atomic, an ion
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. So we know that aluminum has a charge of
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plus three, and we know that sulfate has a
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charge of minus two. So this is actually very
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similar to the oxide example. So we need to
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aluminum's for every three pieces of the sulfate. And
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when you're writing, um, specific units for quality
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atomic islands, you want to make sure that you
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add a parentheses over the whole species and then the
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number. So when you're writing this, you don't
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want to write the number next to something like four
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. So if someone reads it, it actually doesn't
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make a whole lot of sense on it. Actually
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looks like you want 43 atoms of oxygen in your
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molecule, which doesn't make any sense. Um,
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And when you put the parentheses and the three,
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um, it tells us that you're talking about three
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units of the self aid and so we know that
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this is again a molecule because we accounted for the
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charge so that the species is a neutral species