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Molecular Formulas

In chemistry, a molecular formula is a way of expressing information about the proportions of atoms that constitute a particular chemical compound, using a single line of chemical element symbols, numbers, and sometimes also additional symbols, such as parentheses, dashes, brackets, etc. For example, the molecular formula for glucose is CHO, which means that each molecule of glucose contains one carbon atom, six hydrogen atoms, and one oxygen atom.


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Video Transcript

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