 So, today we're going to talk a little bit about chemical bonding. Chemical bonding occurs so that elements or atoms can join together so that they get a whole set of electrons or achieve the octet rule, basically. So, the first type of compound we're going to talk about are ionic compounds. Ionic compounds are formed between positive ions and negative ions. So, positive ions are usually formed by atoms of metals, negative ions are usually formed by atoms of non-metals. So, in essence, if you have a metal paired with a non-metal, you can make an ionic compound. So, ionic compounds, when we put these ions together, they have to be put together in a way so that the compound itself is neutral. So, if we're going to make formulas of compounds, say we're going to put sodium with chlorine. First we have to determine what the ions are for each of these elements. Sodium is a group 1A metal, so it has a plus 1 charge. Chlorine is a group 7A metal, so it forms a negative 1 ion. Since these numbers are the same, they cancel each other out, and we can put these together just one sodium and one chlorine to form sodium chloride. So, if they are the same number, opposite charge, you can just put them together one of each and they cancel each other out to make a neutral compound. However, if their charges are different, the numbers are different, you have to go through a process to make sure that your compound is neutral. So, let's say we put sodium with sulfur. Sodium being a group 1A metal forms a plus 1 ion. Sulfur being a group 2A metal, I'm sorry, 6A metal, forms a minus 2 ion. Your numbers do not cancel each other out. The easiest way to determine what the ratio of your atoms should be in a compound is the process of crisscrossing. So, if I write my 2 ion symbols, if I take the number from one symbol, it becomes the subscript for the opposite atom. The number of the charge of the nonmetal becomes the subscript for the metal. So, that means we need two sodiums and one sulfur to make a neutral compound, and that would be the formula for sodium sulfide. So, anytime you have two different numbers, you can use the crisscross process to determine what the subscript should be in your formula. Another example, we could put magnesium with nitrogen. Magnesium is in group 2A, so it forms a plus 2 ion, so that's its charge. Nitrogen is in group 5A, so it forms a 3 minus ion. Our numbers are different, so we're going to use the crisscross process. We need three magnesiums. We need two nitrogens. So, your formula will be Mg3 and 2. That means we have three magnesium ions and two nitrogen ions in this compound. So, that is how we would determine the formulas for these. The next step would be naming these compounds. To name an ionic compound, first we're going to look at the metal. The metal, you would just write the name. The non-metal, we use its name by changing and then change the ending to IDE. So, chlorine becomes chloride. So, we change the ending of the non-metal. So, it becomes sodium chloride. For this one, again, metal is just the name of the metal, sodium. The non-metal, we change the ending of its name to IDE, so sulfur becomes sulfide. So, sodium sulfide. And the last one over here, the metal, magnesium. The non-metal is nitrogen. We change the ending to an IDE and it becomes nitride. So, it will be magnesium nitride. Okay? Notice that the subscripts were not involved in the name at all. Just because we have a 2 with the sodium sulfide, we don't indicate that anywhere in the name. We have three magnesiums and two nitrogens. We don't change the name at all to indicate how many there are because there is only one way that magnesium and nitrogen can go together to form a neutral compound. So, that's how you would put together elements that are part of the representative elements, the group, the A groups, 1A through 8A. We can also talk about the transition metals, the B groups. The transition metals are different in that they can form multiple ions. Their group name, group number, doesn't necessarily tell you how many valence electrons they have or how or what their charge is going to be. Okay? So, you would, it would be indicated either in the formula or in the name what the charge of the ion is. So, for transition metals, they can have variable charges. Some examples. Copper. Copper can form two different ions. It can actually form a copper that's a plus 1 ion. It can also form a copper ion that's a plus 2. To distinguish between these two when we name them, we are going to indicate the charge of the ion. So, this would be copper 1 ion because it has a charge of 1 plus 1. This would be the copper 2 ion because its charge is 2. Okay? Same thing with iron. Iron can have a 2 plus charge and a 3 plus charge. So, this would be iron 2 ion. This would be iron 3. So, you must indicate what the charge is with the name when you're naming compounds that have a transition metal in them. Okay? Of course, there are exceptions to every rule. So, need a Roman numeral in the name to indicate charge except for silver, cadmium, and zinc. These are not variable. Even though the transition metal silver only forms a plus 1 ion, cadmium and zinc only form plus 2 ions. Since they're not variable, you don't need a Roman numeral for these. Okay? So, let's make some compounds with transition metals. So, let's say we wanted to write the formula for copper 2 sulfide. First, we have to figure out what the ions are. So, we have copper 2. Since it gives us a Roman numeral, it tells us the charge of the ion. Sulfide is the sulfur ion. So, you go to the periodic table. It's in group 6A. It forms a minus 2 ion. To write the formula, we need to have a neutral charge balanced formula. So, since these are the same number, they balance each other out so we can just put one of each. And this would be the formula for copper sulfide, copper 2 sulfide. Okay? If it was something like iron 3 oxide, first determine the ion for the metal. It's iron. The charge is 3 plus because the Roman numeral indicates the charge. Oxygen is group 6A element. So, it'll have a minus 2 charge. Since our numbers are different, we'll use the crisscross process. So, the correct formula would be Fe2O3. So, that's going from name to formula. We can go the other direction and go from formula to name. So, if we had something like Z, Ni2S. We want to name this. Okay? We know that the name, first we write the name of the metal and we write the name of the nonmetal. Ni is nickel. S is sulfur. We changed the ending to IDE. So, sulfide. However, there's one more piece to this name. Nickel is a transition element. So, if it's a transition element, we have to include a Roman numeral that tells us the charge. So, to determine the charge of a transition metal, we can't look at the periodic table. So, we're going to use the subscripts given in the formula to figure out its charge. So, the way we crisscrossed here to figure out subscripts, we can go in reverse to figure out the charges. So, I'm going to take the two, crisscross it up this time. That's the charge of the sulfur. Since there's no subscript here, we assume it's a one. We crisscross it and that becomes the charge. That must be the charge of the metal. So, it's plus one. Since this is their charge, that is the Roman numeral we need. Nickel one, sulfide. So, from this, you can make name or write formulas for ionic compounds that contain regular group A representative metals and those that contain transition elements.