Hi, again. In the last lecture, I outlined a set of rules for assigning oxidation states to atoms and compounds. In this lecture, we're going to learn the modern nomenclature rules so that we know how to properly name ionic compounds. Once again, it's a good idea to have a periodic table handy. So either pull out your trusty hard copy, or pull out a copy on your virtual desktop, so that you can either see it at the same time as the lecture, or you can toggle back and forth for quick and easy reference. I'll be toggling back and forth to the periodic table, during the lecture, as well. Let's start by reviewing oxidation states. You might want to print out the oxidation state rules, as well. So you use them when you are practicing assigning oxidation states. You need to be very adept at doing that in order to properly name bionic compound. There's a copy of the list of oxidation state rules in the useful information section of the course main page. Remember we're going to follow the rules in order. The first rule is that pure elements are all zero. So even if its a molecule that has many atoms in it If it's a pure element, for example, O2, then the oxidation state of both oxygen's in diatomic oxygen molecule is zero. And then we're going to go through the rules such that the more electronegative element gets the bonding electrons. Fluorine is the most electronegative element, so it tends to gain electrons to become the fluoride anion. The alkaline metals, the alkaline earth metals tend to lose their electrons to have charges of plus one and plus two respectively. Aluminum also tends to lose electrons. In this case, it loses all three to have a plus three charge. Now we're getting to the rules where things kind of vary, depending on what the other atom is in a compound. Hydrogen is usually plus one and that's what it is if it's in a compound with other non metals. But if it's in a compound with a less electronegative metal Then the hydrogen would take the electrons away from the metal. And it can be minus one, which would be hydride. Oxygen is usually minus 2, but not always. We see already, up at the top, that oxygen can be zero in a pure element. And halogens are usually minus 1. So that's just a quick review of the oxidation state rules. If you want to have some practice applying those, please go back and either look at video for lecture number eight for this week, or you can do some of the exercises that are provided. We're going to use the oxidation state rules when we name ionic compounds. When we name ionic compounds, the first thing we need to do is name the ions that make up the ionic compound. An ionic compound is always a combination of a cation and an anion. So at least one cation and at least one anion, sometimes you have more than one cation and more than one anion Ion. The simplest cations are monatomic cations. So these are species where you have a single atom that has lost some electrons, and it now has a positive charge. When you're naming a monatomic cation, you don't need to change the name. So strontium after its loss two of its electrons it's still called strontium, but often will now say it's strontium cation. When you're naming a monatomic anion, you're going to change the ending of the name of the element to ide. So, for example, fluorine when it becomes f1 minus is then fluoride. There are two cases for naming ionic compounds. The first case is the easiest case to name and that is when the cation can assume only a single oxidation state. And this is true for the main group elements of the alkali metals, and the alkaline earth metals, and a few of the transition metals, not very many. We'll talk about which ones. And then aluminum tend to have very common oxidation states that are always the same. So in this case, the name is very simple. You would name the cation and then there's a space between the words and then you name the anion and remember when you name the anion, the ending of the word ends with the suffix ide. Let's take a quick look at the periodic table. To see which of the cations can assume only a single oxidation state. So here's the periodic table. Once again, I'm going to move hydrogen. I'm just going to get rid of it. I'm going to put it over here in the middle. Just bugs me where they put it on this one. There's a reason they put it there, it's just not my favorite place to have it. So remember, the main group elements are groups one and two and groups 13 through 18. In the main group elements, alkaline metals, when they lose electrons, assume an oxidation state of plus one always. So sodium can either be sodium metal, which is zero, or it can be sodium cation, which is always plus one. There are no sodiums that have a charge of plus two and there are no sodiums that have negative charges. Same is true for the alkaline earth metals, except in this case they lose both of their electrons. So calcium can either be metallic calcium which is calcium zero, and that would be calcium with 20 electrons. Or it can lose both of it's electrons, to assume a charge of plus two. And then we get to the transition metals which are not main group elements. For the transition metals we usually cannot apply this rule where we just name the cation and then the anion. There are a couple of exceptions though. Silver by far has the most prevalent oxidation state of plus one. So I'm just going to draw a little arrow to it. Plus one, there are some silver plus two compounds out there but they're very few and far between. So, for the most part we say silver has an oxidation state of plus one. Zinc almost always has an oxidation state of plus two and then aluminum has an oxidation state of plus three. Do you see this little diagonal here from silver to zinc to aluminum, this little diagonal? Plus one, plus two, plus three. So when we're naming compounds of the alkaline metals, the alkaline earth metals, or silver, zinc, or aluminum, we're just going to use this rule where we're going to name the cation, then name the anion. We don't need to say how many cations are in the compound, and we don't need to say how many anions are in the compound because we can figure that out from the oxidation states, which are not variable for these species. Let's do some examples. So the compound of potassium and iodine is called potassium iodide that changes the name of the anion tab ide at the ending. You see how that works? If I have a magnesium bonded to chlorine, there will always be two chlorines there. And they will take the electrons away from the magnesium to form chlorides. So each chlorine has taken one electron away from the magnesium. The magnesium then loses both of its valence electrons to make magnesium chloride. And I want you to be noticing here, that in the name of this compound, I don't say that there's two chlorides, do I? I know that must be true because magnesium's common oxidation state is plus two, or two plus. Okay, so since chlorine is CO1 minus, there's got to be two chlorides for every magnesium. [NOISE] This compound of aluminum and carbonate is just called aluminum carbonate. I don't say anything about many aluminum there are, I don't tell the person about many carbonates there are because all that can be figured out by using the common oxidation states. And finally, this compound of ammonium and hydroxide is just called ammonium hydroxide. So usually these ionic compounds are a metal and a non-metal, do you see that? But there are some instances where I'd have groups of non-metals that make a cation. Ammonium being the one that we've talked about the most so far. So I can have all non-metals and still have an ionic compound. Okay, now it's your turn to try one. What is the correct name of this compound, K2O? Feel free to look at your periodic table. If we look at the periodic table, we see the potassium is an alkaline metal. So, potassium's oxidation state is always plus one. It's not something that changes. If potassium is in a compound, its oxidation state is always plus one. Oxygen in a compound tends to have an oxidation state of minus two. So, when these species combine in order for the charges to cancel each other out and to balance, we'd need to have two potassiums and one oxygen and that's exactly what we have. When that's the situation, we don't need to do anything fancy with the name. We don't need to outsmart ourselves. So for example we don't need anything that's called a replicating prefix like mono, di, or tri. So we can cross anything that has replicating prefixes out. We haven't talked about doing that yet, have we? So these things that have dipotassium, we can cross out. We know that the anion here is called oxide. So the second part of the name needs to be oxide. So that allows us to cross out a, which is potassium oxygen. Since potassium always has a plus one charge when it's in a compound. We don't need to have anything that tells us what the charge is or how many potassium there are for example. So, we can cross out d and that leaves us with the correct answer which is b. Do you see how I did that? I just follow the rules. So, remember when you have monatomic cations and monatomic anions that can only assume a single oxidation state for the cation. You just name the cation, then put a space and then name the anion right? So the space here. So the name here is potassium oxide very simple. So just to remind you, first of all I'm going to move hydrogen because I don't like where it's drawn on this table. Let's move it over here out of the way. Remember that lithium and potassium and sodium tend to lose their electrons to get a plus one oxidation state. Berilium, magnesium, and calcium tend to lose two electrons to have a plus two oxidation state. And if I move over here to the right side of the periodic table. The halogens tend to gain one electron, the oxygens, the oxygen group, group 16, oxygen, sulfur, selenium, they tend to gain two electrons. But where do these electrons go? When sodium loses an electron, where does it go? And where do these electrons come from? They just fall out of the sky? Of course, they don't. What happens is the electrons are taken from the metal and given to the non-metal. So that's what happened in our case of potassium oxide. Each potassium lost one electron. [SOUND] Okay, so there were two electrons lost from the two potassium' total and so the oxygen then gained those electrons. When the bond formed So that's what happens in ionic bond formation. All right. That's the first case of naming ionic compounds. I have a cation that can only assume one oxidation state when it makes compounds with other elements.
