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Tips for Naming Covalent Compounds - Concept

Teacher/Instructor Jonathan Fong
Jonathan Fong

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 are some tips and tricks for naming covalent compounds. We're working under the assumption that these are binary compounds. So they have two elements in there. And that they're made up of two non-metals, that's why they're covalent.

So just to practice in a stem. So say if I have Oxygen, the stem that I would use would be Ox, and that would be helpful later. So here we have CO2 and so what we'll do is, we're going to follow the pattern, like this. We'll take prefix, then or the first element's name, we'll leave a space. And then we'll use the second prefix. We'll use the stem of the second element, and then you add 'ide' on the end.

So this is a sheet for prefix; first, element's name, prefix, stem and then add 'ide' on it. Or even the first word, if there is one atom, of the first element, you would omit mono as a prefix.

One the second word, you would put mono. So say for example, we have CO2. So we only have one carbon atoms, so we're going to omit using mono. And so we'll just write out the first element's name, carbon. The prefix for the second one, since there's two oxygens, let's take a look at our right column that I've written out the prefixes for you. These would actually be good to memorize here. Then you would use 'di' as the prefix. The stem, since it's oxygen, would be 'ox' and then we add 'ide' on the end. And that's how you name CO2, carbon dioxide.

So say for example, if we have P2O5. So what we'll do is we'll use the prefix. Since there's 2 phosphorus, we're going to put 'di' and then we'll write the whole name out so phosphorus. Then second word, since I have 5 atoms, we go over here 'penta'. Since I have a vowel here, Penta, and oxygen starts with a vowel, we're going to drop the 'a' on the penta. That's only if there's a vowel for the element name, for the element stem. So pentox and then 'ide' on the end always. The 'ide' is always there.

So, say for example if we had, say another one. Say we had SF6. We take a look here, we have pone Sulfur. So mono, well we would omit mono in the first word. So we would just write out Sulfur. Then, on the second one we have 6, so we'll use hexa. Then, here we have fluoring. So we write fluor, because we're only using the stem, and then we put 'ide'. So this would be sulfur hexafluoride.

So if you follow this pattern, naming all covalent compounds will be easy, because all you got to do is, take a look at the number of atoms of each of those elements.

Now on the flip-side, if you want to do a reverse. Say if I was given the name Carbon monoxide, then I would just do the reverse. carbon, since there's no prefix that means there's only one. So I'll write C. Mono on the second word means there's only going to be one atom. And here we have 'ox', so that's oxygen. Then ide is always on the end. So I have CO that we have right here. So we have Carbon monoxide or CO.

So then, we'll do one more example. So say for example we'll do phosphorus trichloride. One more time, phoshorus, no prefix, so I only have one atom of phosphorus. Then tri means I'll have 3 of that elemnt. what's that chlo? Chlo comes from chlorine, so I'll put PCl and then 3, that's the subscript because there's a tri there.

So if you remember what the prefix is and you remember the naming, remember prefix; first element's name, prefix, stem and then 'ide' always goes on the end. Then naming covalent compounds will be a lot easier for you.