What's a polyatomic ion?
So
what
's apolyatomic
ion? Apolyatomic
ion is a group of atoms that has a charge. Here'swhat
I mean. You probably already know that individual atoms can have a charge, they can form ions. So we can get things like Na+, Mg2+, and O2-.Polyatomic
ions orwhat
happens when more than one atoms comes together and they form a big group of atoms and that group of atoms itself has a charge. Sopolyatomic
ions are things like NO3-, so we have one Nitrogen and three Oxygens all connected
together form a group and that whole
group has a charge of one minus (-1). "Poly" means "many," so here,
polyatomic
ions, we're talking about ions that are made up of many atoms, more than one atom. Let me show you a few examples of how this actually works. So here are two of my favoritepolyatomic
ions, Ammonium and Carbonate. Ammonium here is made up of one Nitrogen connected to four Hydrogens and Carbonate is one Carbon connected to three Oxygen atoms. Now the atomsthat are in each of these
polyatomic
ions, they have protons and electrons in them. Sowhat
we can do for both Ammonium and Carbonate is we can count up the number of protons that are in each of these atoms. If I do this for Ammonium I get eleven protons and thereby count up the total number of electrons that are in this whole group, I get ten. So these two numbers don't balance out. I have more protons than electrons which means I have more positive charge, I have I net charge of one plus(+1) because I have one
more proton. So my net charge here is one plus (+1) and
I can write the formula for this
polyatomic
ion, it's NH4 because I have a Nitrogen and four Hydrogens with a plus one (+1). I usually will also take the structure of this Ammonium and put the whole thing in brackets and put a plus outside to indicate that this whole group of atoms together has a positive charge. I can also call this thing a cation, apolyatomic
cation because it iswhat
we can ions that have a
positive charge. Now Carbonate, we can do the same thing with
it. We can count out the total number of protons
that are in the atoms that make it up and we can also count up the total number of electrons
that are in this whole group. We get 30 protons total and 32 electrons total. So we have more electrons and protons which
means we have more negative charge, it is going to have a net negative charge, and since
there are two more electrons it's going to have a net charge of minus two (-2). I
can write the formula for this
polyatomic
ion as CO32-, one Carbon and 3 Oxygens totaling the charge of two minus (2- ) and then I write my structure in brackets and put a two minus (2-) here to show that this whole thing has a net charge of two minus (2-). We call this guy a cation because it has a positive charge so we can call Carbonate apolyatomic
anion for negative ion. As I said before, there are a whole bunch ofpolyatomic
ions that have a small number of them on this list right here. Alot of times people ask me, they say, okay
if I knew Nitrate was NO3 but I didn't know the charge, would it be possible for me to
figure out the charge just on my own? Unfortunately no, it's very difficult to figure
out how many electrons a
polyatomic
ion has and so you need that to figure out the charge.Polyatomic
ions are really important for when you're writing chemical formulas of compounds and since you need to use them a lot, they're one of the things in chemistry that you
really just have to memorize. So I made a video on that! It's called learning
polyatomic
ions and if you need to learn these, which you probably do, you might want to check that video out. I talk about a number of strategies that you can use to better learn these. Also, if you're interested in the actual bonding that's taking place in the atoms that make up apolyatomic
ion, it's a little bit more advanced but you might want to check out the video called "How arepolyatomic
ions made?" where I talk about the covalent and ionic
bonding and sharing of electrons that takes place as these
