AP Chemistry Naming Compounds

Hello, and welcome to Educator.com; and welcome to the first lesson of AP Chemistry.0000

Today, I'm going to start by discussing the naming of compounds, because we have to know what it is that we are dealing with in order for us to jump into the chemistry.0005

So, let's get started.0013

OK, so this is, of course, the periodic table, and I'm just going to do a quick overview of the periodic table, just to get a sense of where we need to be, because this periodic table is what you are going to be using all the time--it's going to be your primary reference in chemistry--as you already know.0017

Over here, on the left, we have this first column; these are called the alkali metals.0033

Actually, you know what?--let's sort of break it up broadly.0040

Generally, everything from about right here onward--everything that is blue, and this orange right here--so the whole left side--these are all metals.0044

Up here, starting with boron, silicon, arsenic, tellurium--everything here and up to the right--those are going to be nonmetals.0053

So, as you can see, most of the periodic table--most elements (naturally occurring elements) consist of metals.0060

These over here are called the alkali metals; the second column is called alkaline earth metals; these here, in the middle--these are called the transition metals.0066

These over here are called the noble gases, basically because they are unreactive.0078

These are called the halogens.0084

These are the standard nonmetals.0086

The only thing on the left that is a nonmetal is hydrogen.0088

Now, let's talk about some of the diatomic gases.0091

There are certain gases (well, certain compounds; not just gases, because bromine is actually a liquid)--certain compounds that occur...0096

The periodic table lists actual atoms; astatine, iodine, bromine, chlorine, fluorine, oxygen, nitrogen, and hydrogen--they occur as diatomic gases.0105

In other words, there are two atoms that make a molecule of that in the natural, normal state.0116

What you are breathing right now is nitrogen and oxygen gas; not nitrogen and oxygen atoms, but there are two atoms stuck together to form a molecule.0121

That is really all that you have to know.0132

These numbers up on top (the ones right below the symbols): those are the atomic numbers--that is the number of protons and electrons in a neutral atom.0135

This number, right down below it (which, for many things, is almost double the atomic number)--that is the atomic mass; that is an average of all of the masses of the isotopes, depending on the frequency of occurrence of the particular isotope.0144

Again, if any of this is strange--things or words like isotope and stuff--I would definitely urge you to look through it in your books, but for all practical purposes, it won't come up all too often.0162

So, I just wanted you to get a quick overview; and now, we can jump into actually naming the compounds.0174

Because, before we do anything else--many of the problems are not going to actually have equations for us, or symbols for us; they're just going to give us names of compounds.0179

We have to know what it is that we are writing, so we can write an equation--all chemistry begins with a chemical equation.0187

OK; let's start off, quickly, by talking about what ions are.0193

Ions are atoms that have lost or gained an electron--that is it; lost or gained one or more electrons.0201

Your atoms (your naturally-occurring atoms) are neutral; in other words, they have the same number of protons and electrons, which makes them electrically neutral.0223

If I add to those, or if I take away from those, all of a sudden they become charged particles.0231

Positive ions are called cations, and negative ions are called anions.0237

So, an example of that would be something like this: Mg²⁺ is a magnesium atom that has lost two electrons.0252

Because an electron is the thing that is being added or subtracted, when we add (electrons are negatively charged), it carries a negative charge.0259

So, for example, O^2-; that is an atom that has gained two electrons, so now it's carrying two extra negative charges.0268

Magnesium lost two electrons, so now it has two more positive charges than it does negative charges; that is why we put the ²⁺.0277

Fluorine is ^-; potassium is ⁺; aluminum is ⁺³; iron(II) is that; there is also an iron(III)--and we'll talk about that in a minute--why it is that certain transition metals actually can lose more than one electron, and they have different oxidation states.0285

That is it--ions, and the first thing that we're going to discuss, of course, is ionic compounds: simple binary ionic compounds, where the cation is made of one element and the anion is made of the other element.0306

Let's go ahead and get started.0319

OK, so now let's go to ionic, and we're going to go from the symbol to the name.0323

We need to be able to go from the symbol and be able to name the compound, and we need to be able to go backwards (from the name to the symbol).0331

So, from symbol to name--we'll do that first.0338

NaCl...now, if you look at your periodic table, you're going to notice that the alkali metals on the left, the alkaline earth metals (which is the second), and then on the right (if you ignore the noble gases), you're going to have the halogens, and then you're going to have the next group and the next group, working to the right.0344

As it turns out, the metals always lose electrons; nonmetals always gain electrons.0365

So, when we're talking about ionic compounds, it's always going to be the metal that is going to be positive, and it's going to be the nonmetal that is going to be negative.0376

Now, what we do when we put together ionic compounds is: we are just putting them together in such a way that we actually cancel the charge.0385

But again, we will get to that in just a minute, when we're dealing with name-to-symbol.0394

So, sodium...this NaCl, the name for this is sodium chloride--that's it.0399

Anytime you see something like this, basically, what you do is you take the name of the metal (sodium); you take the base of the nonmetal, and you add -ide to it; that's it.0404

How about MgBr₂; OK, this is just magnesium, and this is bromine, so it becomes "bromide."0422

That's it; it is always consistent--it's the name of the cation first (the positive, or the name of the metal, first), and then the name--the root of the nonmetal, plus -ide.0436

All binary ionic compounds are named like this.0446

How about something like this: Al₂O₃; don't worry about what the numbers mean yet--we'll get to that in just a minute.0451

This is aluminum oxide.0460

And then one more for good measure: K₂S; this is potassium sulfide.0465

That's it; very, very nice.0477

OK, so now we're going to do to ionic, and we're going to go from the name to the symbol.0479

OK, so if I see something like calcium oxide, how do I symbolize that?0489

Well, here is where we have to actually look at the charges; and the charges come from their arrangement on the periodic table.0499

The alkali metals are in the first group on the left; when they react with nonmetals, they actually lose one electron; they're in the first group.0506

The things in the second column (like magnesium and calcium)--they lose two electrons when they react.0517

Well, if we go to the right-hand side of the periodic table (ignore the noble gases), the halogens--they actually gain one electron when they react.0525

The next column over (next to the halogens), the one where oxygen and sulfur are--they gain two electrons.0538

Then, if you go one more, you're going to end up with the nitrogen and phosphorus column; those gain three electrons.0544

So, when you're putting ionic compounds together that consist of a metal from the left and a nonmetal on the right, you look at their charges.0553

In the case of calcium, calcium is a 2+ charge, because it's in the second column.0560

Oxygen has a 2- charge, because it is the second column over, ignoring the noble gases; it has a ^2- charge.0566

What we're trying to do here is: we need to combine these in such a way that the charges actually cancel.0574

Here, the positive 2 and the minus 2 cancel, so the symbol is just CaO.0580

In other words, I just need one calcium atom and one oxygen atom to make calcium oxide; the charges balance.0585

OK, now let's do something like sodium sulfide.0594

Sodium sulfide: well, sodium is in the first column, so it has a +1 charge; sulfur has a -2 charge; it's in the second column over from the halogens (again, ignoring the noble gases).0603

Well, this is a +1 and this is a -2; in order to balance this charge, this +1 needs to be +2 to balance this -2.0615

Therefore, we need 2 sodiums; so, the symbol becomes Na₂S.0623

I need two sodiums for a total 2+ charge to balance the -2 charge.0628

And again, all ionic compounds have to be neutrally charged--their charges have to balance.0632

Let's do something like aluminum iodide.0641

Aluminum is in the 1, 2, third column over on the periodic table, when you actually skip the transition metals (we're going to get to the transition metals next--they are handled a little differently).0652

So, from your perspective, the first column, the second column...you skip the transition metals, and you go to the other column, where aluminum is.0661

That is a 3+ charge, so everything in that column carries a ³⁺ charge.0670

Al³⁺; and iodine is a halogen, so it has a -1; well, how many iodines do I need to balance the 3+ charge? I need three of them.0675

So, this becomes AlI₃, aluminum iodide.0684

Let's try calcium phosphide.0690

Calcium phosphide is Ca²⁺, because calcium is in the second column; phosphorus is in the third column over, so it carries a negative 3 charge when it's reacting with a metal.0701

Well, how do I balance 2+ and 3-? I can't do it directly, so I need the least common multiple of these.0711

The least common multiple is 6.0717

In order to make 6 positive charges, I need 3 calciums; and 6 negative charges--I need 2 phosphoruses.0720

So, this becomes calcium phosphide; that is it.0729

You're just taking a look at the charge on the anion and the cation, and you're arranging them--taking specific numbers of them and putting them together so that the charge is 0--that's all you're doing.0732

We'll finish it off with aluminum sulfide.0743

Aluminum sulfide: OK, we said that aluminum was 3+, and sulfur is in the column with oxygen, so it is a 2-; so again, we have to make 6, so we end up with Al₂S₃, aluminum sulfide; that is it.0750

OK, now we'll do polyatomic anions.0765

Polyatomic anions: again, you have seen them before; polyatomic anions are anions that are made of more than one atom.0776

Some examples would be something like ClO₃^-; that is chlorate; SO₄^2-; that is sulfate; maybe PO₄^3-; that is phosphate.0788

Let's see...ClO₂^-; that is chlorite; and one of the things you are going to notice with the polyatomics--they generally tend to end in -ate or -ite--most of the time.0808

There are some exceptions, like, for example, the NH₄⁺; that is called ammonium.0820

Now, of course, you have seen lists of polyatomic ions; and there is a page, a list, in your book, of polyatomic ions; or, you can go on the Internet, and you can find a list of polyatomic ions--some short, some long--and it lists all of the polyatomic ions that are available.0828

These are treated exactly the same way as the regular atomic anions, in the sense that you are treating them as a whole.0846

When you name them, you just basically use the entire name of the anion; so these actually work out really, really easily.0855

So, let's go from symbol to name first.0863

Symbol to name: for example, if I saw something like NaClO₃; well, Na is sodium, and ClO₃...when I look it up on the polyatomic ion chart, it is chlorate; so the name is sodium chlorate--very, very simple.0870

If I have something like KClO, well, K is potassium, and if I look up ClO, it is going to be hypochlorite.0891

So, it is potassium hypochlorite.0902

If I had Ca(CN)₂, well, Ca is calcium, and CN--when I look it up, it is cyanide; so it is calcium cyanide.0908

So it's very, very simple--you are handling it the exact same way: the name of the metal first, and then the name of the polyatomic anion.0923

Again, these are treated as a whole; it's like--just think of it as one unit that happens to have a specific charge on it: it could be -1, -2, -3...that's it.0929

And again, there is a whole list of these atomic...you will use them enough times so that you'll eventually memorize them, or perhaps you already have them memorized.0940

OK, so now let's go the other way; let's go from the name to the symbol.0949

Now, let's go from name to symbol.0955

Let's do potassium phosphate.0960

If you see "potassium phosphate," well, potassium is in the first column; so, when it reacts as an ion, it is K⁺.0963

When you look up "phosphate," it is PO₄^3-; we are doing the same thing.0977

We just need to put them together in such a way that the charges balance.0982

In order for the charges to balance, we need three potassiums in order to balance the three negative charges; so we write it as K₃PO₄: potassium phosphate.0986

How about something like aluminum nitrate?0999

Well, aluminum has a 3+ charge; nitrate, when you look it up--it is NO₃, and it carries a -1 charge.1008

I need three nitrates to balance the 3+ on the aluminum, so it becomes Al, and whenever you need more than one polyatomic, you of course put it in parentheses, so it is written as (NO₃)₃.1016

Now, this three--that means you have three NO₃s; so it's three nitrogens, nine oxygens.1030

Now, let's do one more: magnesium hydroxide.1037

OK, magnesium is a 2+; hydroxide, when you look it up--it is a -1; you need two of these to balance the 2+ charge.1047

So, it is Mg(OH)₂; good--nice and easy.1054

OK, so now we're going to move on to ionic compounds involving transition metals.1060

Ionic compounds involving transition metals: OK, now let's take a look at two compounds, just to start with.1069

Let's take a look at Fe₂O₃, and let's take a look at FeO.1084

Well, if I ask you to just name these the way we have been doing, you take the name of the metal; you take the name of the anion, add -ide to it, and you will get iron oxide.1091

Well, it's true--this is iron oxide; however, there is this other compound, that is FeO; this is also iron oxide.1101

These are two entirely different compounds with completely different chemistry; how do we differentiate between the two?1109

As it turns out, transition metals (all of those things in the middle of the periodic table)--they can actually lose different numbers of electrons--the same atom.1114

For example, you can have iron 2+, iron 3+; you can have manganese 2+, manganese 4+, manganese 6+...so these things--we actually have to specify, in parentheses, in the name, how many electrons it has lost--in other words, its charge.1124

So, in this case (and here is how you actually end up doing it), let's take Fe₂O₃.1140

Fe₂O₃; well, what do we know about oxygen? Oxygen, when it reacts, always carries a -2 charge.1149

There are three oxygens, so the total charge is -6.1156

Well, this -6 has to be balanced by a +6, because this is a neutral compound, right?--it's neutral.1160

This +6 charge is divided among two irons; that means that each iron is carrying a +3 charge; so what we do is: we write III in Roman numerals, in parentheses, right after the iron.1167

So, it's not just iron oxide; it's iron (III) oxide.1183

This thing in parentheses tells me the charge on an individual iron atom.1186

Now, if you want, you can write it as...it depends on your teacher; I actually use Arabic numerals instead of Roman numerals, so I just write iron (3), like this: iron (3) oxide; it really doesn't matter.1191

Some teachers like Roman numerals--it's more traditional; some teachers actually don't really care; but obviously, depending on your teacher...if they want Roman numerals, give them Roman numerals.1204

You don't want to be losing a point here and a point there for silly reasons like that.1215

Now, this one--how about iron oxide: which iron is this one?1220

Well, oxygen is -2; there is only one of them, so it's -2; that means it has to be balanced by a +2.1224

This +2...there is only one iron here, so this is actually iron (2) oxide.1231

So, when we are naming transition metal compounds, we have to specify the charge on the transition metal.1236

The charge is different, depending on how it has reacted: we express that with these parentheses.1243

Let's do a few of them.1249

Let's do Co₂(CO₃)₃.1252

Now, again, these transition metals--they can react with individual atoms, nonmetals, or they can react with polyatomic ions.1267

Here, we have a cobalt that has reacted with a carbonate.1275

Carbonate--when you look it up, you know the name--it's carbonate; the charge on carbonate is 2-.1279

The charge on carbonate is (you know what, I'm going to do this a little lower, so I can...let me put it over here...Co₂(CO₃)₃) -2.1287

There are three of them, so it gives us a total of -6.1300

This -6 has to be balanced by a +6, because cobalt carbonate is neutral; and this +6 is actually divided by...there are two cobalts that are carrying that total of 6 charge, so each cobalt has a +3.1303

So, we name this cobalt (3) carbonate.1321

That is it--very, very straightforward.1327

Let's do one more: let's do Mn(SO₄)₂.1330

When I look up SO₄)₂, or if I know it, I know that SO₄ is sulfate; it has a -2 charge; there are two sulfates, therefore the total charge is -4.1336