Welcome to the second video for chapter 4, section 3 on chemical nomenclature. And we're picking up where we left off with molecular compounds. So if you have a molecular compound rather than an ionic compound, we need to be able to name these with unique and recognizable names in the same way that we needed to name our ionic compounds.
But things are a little bit trickier because we need to know what element comes first. With ionic compounds, we could choose the element that was the cation, which is usually the metal, but here with molecular compounds we don't have any cations or anions and so we need to choose a system to choose which element goes first. And what we do is choose the element that is further towards the left of the periodic table or further towards the bottom.
And essentially what that is is the more metallic element, so the closer towards the metals that that element is, that element goes first. Then we are going to use Greek prefixes to specify any ratios that we need to. So for example, molecular compounds can exist in many different combinations of numbers of the same kind of element.
And we need to specify how many of each type of element are in the specific compound that we're looking at. The one exception is if the first element, there's only one of that, then we can drop the mono prefix. So I've put the Greek prefixes over here just for your reference. We went over those in the ionic compound video, but here they are again.
And so once we've decided which element goes first, we've used our Greek prefixes, we're going to use the "-ide suffix on the second element just like we did with the ionic compounds. So here's an example. We're going to go ahead and name this molecule. It consists of carbon and two oxygen atoms. So we start out by figuring out who goes first. So we need to look at our periodic table and identify which element is further towards the left or towards the bottom. Here carbon is clearly further towards the left, so it will be the first atom. We should choose what prefix we use. Here there's only one carbon atom and it's the first one, so we can drop the mono prefix. So we'll just write carbon and then we'll use our prefix for the number of oxygen atoms and it's two, so di and then oxide. So this is carbon dioxide. All right, let's do a couple of more examples. So this next one, we've got nitrogen and oxygen. So we need to identify which element is further towards the left or towards the bottom. We see that nitrogen is further towards the left, so we will start off with that. We need to use the Greek prefix di for two, di nitrogen, and then there are four oxygens, so tetra. The thing is that now we've got a vowel next to a vowel. So we've got this A from tetra and then we have oxide. So when there's an A next to the O in oxide, tetraoxide is clumsy and so we drop that A and we call it tetraoxide. We can do another one. So phosphorus and fluorine. We look here and we see that phosphorus is further towards the left and the bottom than fluorine. So we will start off with phosphorus. There's only one of it. We can drop that monoprefix and we wind up with phosphorus. Whoops, phosphorus. And then our prefix here is 5-penta. And then our element is fluorine. And so that becomes fluoride. Phosphorus pentafluoride. So that is how you name simple molecular compounds. There are a few special types of molecular compounds that I'm going to talk about, and these are acids. The first kind of acid that we're going to deal with is binary acids, and so those are things that contain hydrogen and then one other kind of element. So for example, HBr is a binary acid and so is HCl. So we'll use these two as examples as we're naming these. If we were just to name these using our rules, we would wind up with hydrogen bromide. And that is, in fact, what this is called when it's in its gaseous phase. But if you dissolve this guy into water, it becomes an acid, and we need to specify that it's acidic. So what we do is we go ahead and look at this hydrogen, and we call it hydro as a prefix. So we use this prefix hydro, and then we take the second element, which is here bromine, and we use an "-ic-" suffix on that element. So bromine becomes bromic. and then we add acid to the end of the word. So if we do this again, we can look at this one HCl. If this is aqueous dissolved in water, it's an acidic solution, and we need to specify that. So it's going to become hydro for the hydrogen, and then chloric, whoops, chloric, it's an L, hydrochloric acid. So that's in a nutshell how you name binary acids when they are dissolved in water. All right, and then the last kind of compound that we're going to talk about are oxyacids. And these are a special type of acid that contain hydrogen, oxygen, and at least one other element. And so often what we'll see is that these are hydrogen combined with a polyatomic ion that has oxygen in it. There's a whole process for naming these, and it always starts out with we need to omit the hydrogen, which means we figure out what our root anion is. So we're going to look and see what... What kind of polyatomic anion is this that's different by one hydrogen? And what we see is this is acetate. It's C2H3O2 minus, or equivalently written a different way, CH3COO minus, but with that extra hydrogen on it. So this is acetate. So once we know that base name of the ion, of the anion, then we can go ahead and name our acid. So what we're going to do is leave out the hydrogen. We're just going to start right off with our anion. And then we're going to think about the ending of that thing. So we're going to change any endings that are "-ate", with "-ic". So we're going to convert this guy over from acetate to acetic, and then we add acid. So, oops, acid not added. Let me just fix that typo real quick. Acid. There we go. So you may recognize this as vinegar, acetic acid. This is vinegar. All right, so let's do a few more. This one we recognize that this is NO3- with a hydrogen out front. That's nitrate. So again, we take this ending and we switch it from "-ate to "-ic", so this becomes nitric acid. All right, so this next one's a little bit tricky. So this is not an anion, a polyatomic anion that you know from the list that I had in the last video. But if you read your textbook, you'll note that if you have a polyatomic that's different than one of the other ones, just based by one oxygen, we've got some naming conventions. So nitrate, one oxygen less than nitrate becomes nitric.
So this is NO2 minus, this becomes nitric. Oh, I'm sorry. This becomes nitrite. Sorry. One oxygen less than eight is "-ite".
So this is nitrite and when we replace that ending the nitrite becomes nitrous. So this becomes nitrous acid. So there's some more naming conventions with the polyatomic ions in your textbook in chapter 4.3.
And I suggest that you read those just so that you're familiar with them. I didn't cover them in depth in either of these videos just for time, but it's a good idea to go ahead and read those. All right, and then the last acid that I'm going to do is this guy.
So this one's a little bit odd because there's two hydrogens, but that's totally just for charge balance, right? Because sulfate, as we recognize SO is a Hydrogen tends to make a plus one cation, so in fact it's all it makes is a plus one cation, so we need two of them for charge balance. This has exactly the same naming conventions as everybody else. This is the sulfate ion and we do our our process. So we take sulfate and sulfur is a little bit odd.
If we just followed the rules this would be sulfic. acid, but it sounds weird, so we use sulfuric. So we just go back to the actual name of the element and then add "-ic". And sulfur just sounds better.
So this is sulfuric acid. So that is a naming convention for the oxy acids.