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## Names and formulas of ionic compounds

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# Common polyatomic ions

## Video transcript

- [Voiceover] When you take
a general chemistry class, you often have to memorize some of the common polyatomic ions. So let's go through a list of some of the ones that
you might see in your class. So we'll start off with Cation here, so a positively charged ion, NH four plus is called the Ammonium ion. And for Anions, there are many
Anions that you should know. CH three COO minus is the Acetate ion. CN minus is the Cyanide ion. OH minus is the Hydroxide anion. MnO four minus is the Permanganate ion. And, when you get to NO three minus versus NO two minus, look at the endings. So NO three minus is Nitrate,
so we have ate suffix, ate suffix here, which means more Oxygens. Versus the ite suffix,
which means fewer Oxygens. So we can see that
Nitrate has three Oxygens and Nitrite has two Oxygens. And that ending is important
because it's gonna help you with some of the other polyatomic ions. For example, let's look at
this next set here of four. And let's look at Chlorate. So Chlorate has three Oxygens. It's ClO three minus one. And Chlorite has fewer Oxygens,
it has two Oxygens here, ClO two minus. So we have ate meaning more
and ite meaning fewer here. What about Perchlorate? So here we have Chlorate, but we've added on a prefix this time and the prefix, per,
means one more Oxygen. So Perchlorate means one
more Oxygen than Chlorate. Chlorate had three Oxygens
and for Perchlorate we add one on and we get four. So Perchlorate is ClO four minus. Next, let's look at Hypochlorite. So we talked about Chlorite up here, so here's Chlorite and then we put a prefix, hypo, in front of it. Hypo means one fewer, so if we look at Chlorite,
we had two Oxygens, we take one away and now
we have only one Oxygen. So that must be the Hypochlorite ion. We could have done this
for a different halogen, here we're dealing with Chlorine, but let's say, instead of ClO three minus, let's do BrO three minus. ClO three minus was Chlorate, here we have Bromine instead of Chlorine, so this would be Bromate. So there's another polyatomic ion and we can do another example. So instead of ClO minus,
which is Hypochlorite, we could have had BrO minus, which would therefore be Hypobromite. So this would be Hypobromite. Alright, let's look at our
next set of polyatomic ions. Alright, so let's get
some space down here. So we have SO four two
minus, is called Sulfate. Right, so we have our ate ending. And then we have four Oxygens, so if we go to three
Oxygens, SO three two minus, this is Sulfite, cause
ite means fewer Oxygens. What about if we took
Sulfate, SO four two minus, and we added on an H plus. So H plus and SO four two minus should give us HSO four and then, instead of a negative two here, instead of a two minus, we
would just have a one minus, because we added on a positive charge. So one positive charge
and two negative charges, give us one negative charge. So HSO four minus is called
the Hydrogen Sulfate ion. You might also hear
Bisulfate for this one. Next CO three two minus
is called Carbonate, so if we add on an H plus
to CO three two minus, we'd get HCO three and
then we go from minus two or two minus, to minus one, 'cause we're adding on
a positive charge here. So HCO three minus is
called Hydrogen Carbonate and you'll also hear Bicarbonate a lot. Next we have PO four three minus, which is called Phosphate. If we add on an H plus to Phosphate, think about what we would get. We would get HPO four and
then instead of three minus, we're adding on positive
charge, so we get two minus. So we call this Hydrogen Phosphate. Alright, let's add on a
proton to Hydrogen Phosphate. So we're adding an H plus
onto Hydrogen Phosphate. That would give us two H's. PO four and we'd go from
two minus down to one minus. So H two PO four minus is
called Dihydrogen Phosphate. Alright, let's continue on. One more set of polyatomic ions to know. So we have CrO four two minus, which is called Chromate. And if we have two Chromiums,
so Cr two O seven two minus this is called Dichromate. Next, C two O four two minus
is called the Oxalate ion. and we have O two, two
minus is called Peroxide. And here we have SCN minus, which we call Thiocyanate. So thio, think about sulfur
if you see thio there. So for our next one, we
have sulfur present again, is S two O three two minus and this one's called Thiosulfate. So you might see a few additional polyatomic ions in your class, but these are the ones that
you see most frequently. So make sure to memorize
your polyatomic ions.