 Welcome to the video naming binary ionic compounds containing variable oxidation state cations. In this video, we'll discuss and give examples of how to name binary ionic compounds containing variable oxidation state cations. Many metals can form more than one type of positive ion, therefore, more than one compound can be formed. For example, FeO and Fe2O3 cannot both be called iron oxide. How can we distinguish between the two different compounds? The rule for distinguishing between two compounds that contain the same elements is to use Roman numerals to specify the charge on the metal cation. For example, in FeO, iron has a charge of plus 2, so this compound would be named iron 2 oxide. How do we know that iron is plus 2? We know this because all compounds must be electrically neutral, and since the oxygen ion is always negative 2, the iron ion, in this case, must have a charge of plus 2. The charge on cation plus charge on anion equals 0. Charge on cation plus negative 2 equals 0. Charge on cation equals positive 2. For Fe2O3, the charge on the iron atom can also be determined using algebra. Charge on cations plus charge on anions equals 0. Here there are two cations and three anions. The charge on each of the oxygen ions is negative 2. 2 times the charge on iron plus 3 times a negative 2 equals 0. So 2 times the charge on iron equals 6. Simplifying this, the charge on iron equals positive 3. The compound Fe2O3 is called iron 3 oxide since the charge on the iron is positive 3. Now we are going to go through some examples. Feel free to pause the video to think about your answers. You can also review any part of the video for help. Example 1. What is the name of the compound whose formula is COBr2? Since there is one cation and two anions, the charge on the cation plus 2 times the charge on the anion equals 0. From the list of fixed oxidation state ions, the Bromide ion has a charge of negative 1. Charge on cation plus 2 times negative 1 equals 0. Charge on cation equals positive 2. The name of this compound is Cobalt2 Bromide, since the charge on the Cobalt is positive 2. Let's look at another example. Example 2. What is the formula for the compound whose name is lead 4 chloride? The IV indicates that the charge on the lead ion is positive 4, and from the table of fixed oxidation state ions, we see that the chloride has a charge of negative 1. Assume that there is one cation. One times positive 4 plus the number of anions times negative 1 equals 0. So the number of anions equals 4. The formula for this compound is PbCl4. Now let's explore one final example. Example 3. What is the formula for the compound whose name is chromium 2 nitride? The 2 indicates that the charge of the chromium ion is positive 2, and from the table of fixed oxidation state ions, we can see that the nitride ion has a charge of negative 3. If we assume that there is one cation, the number of anions works out to be two-thirds. We need three cations for the formula to give a whole number of anions. Three times positive 2 plus the number of anions times negative 3 equals 0. So the number of anions equals 2. The formula of this compound is Cr3N2. Now we're going to work through a few problems. Remember you can pause the video at any time to complete the problem on your own before we show you the answers. What is the correct name for the compound whose formula is FeCl3? The cation name is iron. The roman numeral is 3. The anion name is chloride. So the compound is called iron III chloride. What is the correct formula for the compound whose name is lead 2 oxide? The answer is PBO. You have completed this activity naming binary ionic compounds containing variable oxidation state cations.