M.Ed.,San Francisco State Univ.
Jonathan has been teaching since 2000 and currently teaches chemistry at a top-ranked high school in San Francisco.
Here is some tips, and tricks for naming ionic compounds. An ionic compound always has two parts. A cation, which is a positively charged ion, and an anion which is negatively charged. You might see it as a metal, and a non-metal. Some of those ions are called polyatomic. They have more than one element. They have more than one ions. So you might not just have a non-metal.
For example say if we have NaCl. So the cation always comes first. So we have Na. We will just write the name of it. So you have Sodium. Then Cl. Cl is Chloride, because that's the ion. It's not Chlorine, but its Chloride. How would you find that? Well you would look that up on anion list there you would have. Also the anions generally end in a different ending other than the element name. So you have Sodium Chloride.
Another example could be K2SO4. So let's take a look here. The K is Potassium. We'll ignore the 2 for right now. Then we have SO4. The SO4 is you look it up would be Sulfate, so that's the second word. So this would be Potassium Sulfate. The 2 is there with the Potassium, because Potassium has a +1 charge. Sulfate has -2 charge, so the charges in an ionic compound always need to equal 0. So they always need to be neutral. So that's why there's a 2 there.
Here is the trick. All ionic compounds, they have in general, 99% of the time have one element for the cation. So you have this here. So like Na, K. So regardless of the subscript, you know that that's the first element that you have there. Then whatever is left over for the rest, that'll be your anion like SO4, or Cl.
So let's do a couple more examples. So say for example, if we have Zn and then we have our parenthesis, and then we have (NO3)2. Well let's take a look. Our cation is Zn so that's Zinc. So we'll write that out, Zn ion is Zinc, because they always have the name. Then we have NO 3 with the 2 in parenthesis. The parenthesis gives us a hint that whatever is inside would be our anion. So we looked at NO3, and that's nitrate. So we have Zinc Nitrate.
Now there are some elements that are Transition metals with more than one charge. Like they have Copper. Copper has Cu+ for one of it's ions. Then it has Cu2+ for one of its ions. So Cu+ would be Copper(I). The old school way of saying this would be Cuprous so for Copper(I). Cu2+ would be Copper(II). Copper(I), and Copper(II) with Roman numerals are accepted.
If you notice the Roman numeral is the same as the charge. So Cu+ that would be Copper(I), because its a +1 charge. Cu2+ would be Copper(II), because it has a +2 charge.
Let's say for example if we have CU(I)2, well you know that this is Copper, so we'll write Copper here. Then the (I) right here, that's for iodide. So iodide has a -1 charge. Since there are two of them, we know overall that the anion part would have a -2 charge. So that means that Copper has to have a +2 to cancel out -2. So since Copper is +2, this would be Copper(II) iodide. So it's some of those Transition metals, so watch out. So Transition metals, they could have multiple charges. So Transition metals beware. Multiple charges.
Then, so like I mentioned before, all the cations would have only one element in the beginning. The only exception that's commonly used in High School Chemistry, would be NH4, which is ammonium. So let's say if we had (NH4)2, then we had (NH4)3PO4.
So we have the NH4 here, and that is actually polyatomic, because there is more than one atom there. So this is actually Ammonium. Ammonium is the only cation that you'll use in High School Chemistry that has more than one element for its cation. All the other elemets would only have one element.
So we have Ammonium. Then the rest of these right here PO4, that will be Phosphate. So we have Ammonium Phosphate. So hopefully from the formula, these tips, and tricks will help you in figuring out the cation, and the anion. Now this is different from covalent compounds which use prefixes. Ionic compounds do not use prefixes. There is one exception of an anion that uses a prefix.
So let me show you that here. So let's use Ammonium again just to show. Then there is Cr2O7. So the NH4 we know is Ammonium, and then the rest of this Cr2O7 is dichromate. Now there is a prefix spot here, and that just happens to be the name of the anion that we have here. It's called dichromate. There are two atoms of Chromium, but the name of the anion is dichromate unlike the covalent compounds.
If you need help in writing or naming covalent compounds, then you can go ahead and take a look at our tips, and tricks for covalent compounds. Otherwise remember cations, you would only have one element in the formula with the exception of Ammonium. Some of those cations have multiple charges, because they're transition metals. So the ones in the middle of the periodic table. From that, you would need to check up the charge of the anion to figure out what the charge of that particular cation is.
Remember, whatever is left over, then that would be your anion. Sometimes parenthesis help you out in isolating what the formula of that particular anion would be. So hopefully, these tips and tricks help you in naming ionic compounds. Have a good one.