[Music] right if you look at that list first of all you notice that the most common endings for polyatomic ions are the eight ending at te or the it ending it and occasionally there's actually only two polyatomic ions that have the I ending that includes the hydroxide ion right here and the cyanide ion so besides Cyanide and hydroxide all other uh polyatomic ions have eight or I ending another thing that you notice that all of these polyatomic ions carry negative charges they all have a one minus charge or 2 minus charge or a three minus charge there's only one exception there's one polyatomic ion that carries a positive charge positive one charge and that's the ammonium ion now what's the difference between the eight versus the I ending let's look at this polyatomic ion N3 1 minus is called the nitrate ion N2 1 minus is the nitrite ion the difference in the formula is just one oxygen the formula that has more oxygens has the a tending the formula with less oxygens has I ending normally eight ending refers to more oxygens I ending refers to less oxygen the other thing to notice is the prefix by stands stand for hydrogen bicarbonate ion which is H3 1 minus its other name is hydrogen carbonate B sufate ion can also be referred to as hydrogen sulfate ion B Suite ion is hydrogen sulfite ion meaning these three polyatomic ions have two names bicarbonate or hydrogen carbonate and there's one more hydrogen get get rid of the mon here hydrogen phosphate ion is the same as bif phosphate ion uh let's see now what do we have here we talked about the endings okay if you have more than one polyatomic ions in the formula then you have to use parenthesis calcium hydroxide is the example that we're going to look at calcium and here for polyatomic ions I want you to use the crisscross method it's the most convenient way to figure out formulas of ionic compounds calcium has a two plus charge because it's a group two metal hydroxide is o1 minus you can get that from the list of polyatomic ions which you also have to memorize by your next Quiz and since there's two calcium uh since the charge on calcium is 2 plus and hydroxide is 1 minus we need two hydroxide ions for one calcium ion if you do the crisscross method the two goes next to hydroxide the one next to calcium the fact that you need two hydroxide ions to neutralize the charge on calcium means that you have to put hydroxide in parenthesis and the two goes outside of the parenthesis don't put the two inside the parenthesis because that gives you uh the wrong formula for hydroxide hydroxide is always one oxygen one hydrogen so the two goes outside of the parenthesis however if you have only one hydroxide such as sodium hydroxide sodium has a one plus charge hydroxide one minus charge then we don't use parenthesis NaOH is the correct formula for sodium hydroxide if you put parenthesis around hydroxide that would be incorrect because we are only allowed to use parenthesis if there's two or more of the polyatomic ions present in the formula lithium phosphate lithium carries a one plus charge phosphate is a three plus charge the three goes next to lithium one next to phosphate we need only one phosphate but we need three lithium ions lithium is not a polyatomic ion that's why we don't use parenthesis there are three lithiums here not one but three but we don't use parenthesis because this is a monoatomic ion parenthesis are only used for polyatomic ions when there's two or more of them another thing to pay attention to in terms of ending there's the I ending the eight ending and the I ending whenever you see I and eight ending think that this is a polyatomic ion sulfite is s SO3 2 minus sufate S so4 2 minus both of these are polyatomic ions I ending ID endings refers to the non-metals or the monoatomic ions that are on the right of the zigzag line unless you have hydroxide and cyanide other than that IID ending is associated with nonmetals so to come back to this sulfide is S2 minus and just to summarize whenever you have to name a compound the first thing you should ask yourself is the following this the compound have a metal and a non-metal if the if the answer is yes then you have an ionic compound if the answer is no then you have a calent compound and we'll talk about coent compounds next in the next video then uh concentrate on the metal and ask yourself is the metal a main group element meaning does it come from group one two and three or is it a transition metal is it in the middle of the periodic table if the metal that's part of the compound is a main group element then you can get the charge of the metal from the periodic table the charge of the metal equals to the group number if the metal is a transition metal on the other hand then you have to figure out what type of transition metal is it does it form one charge or does it form two different charges if it forms only one charge like silver or cadmium or nickel then there's only one name we don't have a new name you don't have to use Roman numerals if the transition metal forms two different charges you have to use the old and the new name and then go back to the non-metal figure out if the non-metal is a monoatomic ion and what do I mean by monoatomic I mean is that one of these non metals on the periodic table those are called monoatomic or is it a polyatomic ion if it's a monoatomic ion the ending is I and the charge of the nonmetal comes from the periodic table if you have a polyatomic ion the ending is most likely eight or I occasionally it could be I only in the case of hydroxide and cide and here's some examples how we can name ionic compounds with polyatomic ions cupric acetate write down the formula for the cation and the anion cupric means copper with a two plus charge acetate is a polyatomic ion here's the formula it has a one minus charge apply the crisscross method make sure that you have the lowest possible number and since we need two acetates ions we place those in parenthesis and the two goes outside of the parenthesis feris hypochloride Ferris is a transition metal the O sending tells us we have to use the lower of the two possible charges which is the two plus charge and hypochlorite is CL 1 minus r cross the charges and we end up with this formula since we need two hypochlorite ions we place these in parentheses and the two goes outside ammonium D chromate now this is a compound that has two polyatomic ions the cation is polyatomic ion and the anion is a polyatomic ion one plus charge versus two minus charge looks like we need two ammonium ions that's why we're going to place the ammonium in parenthesis and the two go right afterwards and you can do the rest on your own and I'll stop here the next video will be on coent compounds