well hello again and welcome back to get chemistry health.com my name is Dr Kent and in this lesson we're going to discuss polyatomic ions now you might recall a previous lesson on monoatomic ions that dealt with ions formed from just a single atom so monoatomic this lesson is going to focus on polyatomic ions ions that are formed from many atoms and before we get too far into this I highly encourage you to follow the link below here and Download a pdf from getchemistryhelp domcom that really summarizes a lot of the rules and the patterns that I'm going to show you on how to name polyatomic ions now before I show you any of those though I just got to admit there are some polyatomic ions you're just going to have to memorize they really don't follow much in the way of patterns so depending on your class and your instructor they may ask you to memorize some or all or even more than this but your best bet with any of these is just your friend flash cards so if you have to memorize these go ahead and just put C2 h302 negative on the front and acetate on the back c42 negative on the front and chromate on the back and just memorize them but fortunately there are many others that I can show you patterns and rules for so you can name dozens of other polyomics without having just to flat out memorize them so first let's look here at the periodic table now the polyatomic ions typically form from the non-metals and the non-metals that are most important are these right here I'm highlighting so these non-metals like to combine with oxygen to make a series of negatively charged ions or annion so since they're combining with oxygen and they're making annion we call them the oxy anion now there are a few rules rules and patterns that I can show you though that tries to determine how many oxygens these non-metals combine with and the ones I want to show you are called the eights ions so all of these will end in eight so Boron will make borate carbon will make carbonate nitrogen will make nitrate chlorine will make chlorate Etc so let's go over here and look at these eight ions so borate bo33 neg carbonate co32 negative nitrate NO3 negative phosphate p43 Nega and so on now when you first look there doesn't appear to be much in the way of patterns but there are a few for example if I highlight this Square in the middle how many oxygens do all of these polyatomic ions have well they all have four don't they how many oxygens do all of the eight polyatomics on the outside have well all of these eights have three so there's one pattern for you what's the charge well there are a few patterns here too notice all of the ones here in the First Column are all one negative the ones in the second column are two negative the ones in the third column from the right are three negative now there aren't any polyatomics that form with Florine and there aren't any that form with oxygen but the first one there is is one negative the second one there is is 2 negative the third one there is is 3 negative and one last pattern I could show you is if you look down a group like this if you know chlorine is three oxygen and a negative well right under it bromine three oxygen and a negative is bromate iodine three oxygen in a negative is iodate how about sulfur and selenium well if you know sulfate as four oxygen and two negative then selenate is four oxygen and two negative so just the way this repeats so does this one how about phosphorus and arsenic well phosphate four oxygen 3 negative arsenate four oxygen 3 negative okay so once you know how to name the eights then I can show you a few simple rules that can multiply this many times over so for example the ones I just shown you were the eights the ones right here the ones that end in the suffix 8 so for example chlorate chlorate we saw was cl3 negative well if I look on this chart this shows the increasing number of oxygen atoms this says if I add an oxygen atom to that formula then it becomes per whatever the root is eight so chlorate what would per chlorate be well I would add an oxygen to it so chlorate with cl3 negative per chlorate would be cl4 negative well how about chlorite okay well chlorite tells me one less oxygen so chlorite if I want one less must be cl2 negative how about hypochlorite well hypochlorite is another less oxygen now we're down to two less oxygen than the eight so hypochlorite would be CL negative okay so let's just go through and practice a few of these so what's the sulfite ion so I'm looking for I okay well sulfate if you have your PDF in front of you or if you remember sufate is in that Center box so four oxygen it's in that second column so two negative so sulfate is 4 2 negative sulfite would have one less oxygen so it must be S SO3 2 negative how about hypo phosphate okay so hypo phosphate so we're looking for this one down here well phosphate phosphorus is in that Center box so it's got four oxygens and it's three columns over from the right so it's three negative well now we're all the way down here so that means we've lost two oxygen so hypo phosphite soad of P4 must be po2 but still three negative the charge doesn't change only the number of oxygens changes how about per bromate so now we're up here on this one per eight well that means that we gained an oxygen well what's bromate bromates on the right hand side on the outside that box so three oxygens it's just in that First Column so one negative so we're going up here to per bromate so instead of br3 negative now we add an oxygen so it must be BR4 negative how about one more nitrite okay just it okay nitrite tells me one less oxygen than nitrate so what's nitrate well nitrogen is outside that Center box so it only has three oxygens and it's the first one in that row so it's one negative so nitrite tells me it's got one less oxygen so instead of NO3 it would be NO2 negative now let's try a few going the other way what would io2 negative be okay well what do you know for iodine what's the eight what's iodate well iodate iodines on the outside so three oxygens in that First Column so one negative that's iodate so what's io2 oh that has one less oxygen so this must be iodite ion how about aso2 3 negative okay as arsenic is in that Center box so it normally has four oxygens and it's three columns over from the right so it's three negative but we're at aso2 so we've lost two oxygen so we're down here so instead of arsenate now we're at hypo arenite so this would be the hypo arenite ion how about se3 2 negative okay well what selenium normally do for the eight well it is in that Center box so four oxygens it's two columns over from the right so two negatives so that would be selenate we have three so that means from four to three we've lost one so we've gone to selenite ion now another way to make polyatomic ions is by taking the ones I just shown you and adding a hydrogen ion to it or just H+ so for example let's say I had carbonate carbonate is CO3 2 negative that's just the carbonate ion well hydrogen carbonate would just be like I added an H+ to it so if I added an H+ to carbonate that would become hc3 the two negative and the positive will combine to be a single negative so this would be hydrogen carbonate ion what if I had sulfate well sulfate is S so4 2 Nega so what would hydrogen sulfate be well just think of it like adding an H+ so hydrogen sulfate would be hso4 but two negative and positive would combine to be a single negative so that would be the hydrogen sulfate ion now this even works with monoatomic ions like we saw in a previous lesson so for example sulfide just sulfur by itself S2 negative that would be sulfide so what would hydrogen sulfide be let's just write that first hydrogen sulfide well just think of it like you took sulfide and you added an H+ to it so that would become HS the two negative and the positive would combine to be negative how about find phosphate well phosphate is 3 negative so in this case we could actually add one or two hydrogens to it and it would still remain a negative charge if I added one hydrogen to it it would become h po4 2 negative if I added two hydrogens to it it would become h two P4 now just a single negative but they're both still polyatomic ions so this one I would call hydrogen phosphate this one with two hydrogens I would call Di hydrogen phosphate and sometimes just to clarify that there's only one some people will call this monohydrogen but not always so if you just hear hydrogen you can assume they mean one otherwise they might call it monohydrogen for one or dihydrogen for two okay so let's go through and do a few examples of these so hydrogen hypos sulfite so hydrogen tells me we're adding H+ hyposulfite that tells me we're down here so I need to figure out what sulfate is that's always the place to start well sulfate is s so42 minus so hyposulfite means I went down here and I lost two oxygens so instead of s so4 I'd have so SO2 but still 2 negative so if I combine that hydrogen ion with so SO2 2 negative what do I get well I get H O2 but now just a single negative how how about hydrogen selenide hydrogen H+ selenide oh look I it's not I it's I so I tells me it just came from the non-metal by itself so this is one of those monoatomic ions we discussed in a previous lesson well selenium if you look on your periodic table is two away from the noble gases so it likes to be 2 negative so if I combine those two I would get HSC single negative that would be hydrogen selenide ion how about dihydrogen borate ion well dihydrogen so two hydrogens what's borate so we're looking here Boron is outside of that inner Square so it has three oxygens but it's the third column over so it's three negative so if I combine these together two H+ and a three negative I'm going to get H2 bo3 and what's the charge well two positives and three negative gives me a single negative that would be dihydrogen borate ion okay let's do a couple the other way hydrogen sulfur oxygen four of those and a negative so we know this part was an H+ so what would the rest of it be well if I took an H+ out of that that would leave me an S so42 minus what's s so42 minus called well s so42 minus is sulfate so this must be hydrogen sulfate how about H2 aso3 negative H2 tells me I added two H+ so what would have been left if I if I took away two H+ that would left me aso3 but now my negative would have been 2 two larger so it would become 3 negative but what's that well I'm not sure but I know aren arsenic normally makes arsenate that's in that Center box so it normally has four oxygens and a three negative but I'm at three oxygen so I'd be down here so what is that well that's arenite so what do I have I have two hydrogens and an arite so I would call it dihydrogen arsenite and we should write the word ion technically well there you go I hope you enjoyed that long lesson on polyatomic ions for much more practice with naming ionic compounds please come visit me at get chemistry help.com and we will see you again next time thank you