 All right, the next type of conversion you have to be able to do for stoichiometry is the mole particle conversion. It's a little bit more difficult than the mole volume one for a couple of reasons. First there's a terminology thing. The word particle is just a generic term. It refers to whatever that particular substance is made of. And that changes from one substance to the next. This word particle in questions will replace with words like molecules, atoms, and formula units depending on the type of substance that we have. The equivalence is always one mole equals 6.02 times 10 to the 23rd. It's a plain old counting unit like dozens or gross or anything like that. And it can literally be anything that you have a mole of. You can have a mole of donuts. One mole of donuts would be 6.02 times 10 to the 23rd donuts. You can have moles of sand. One mole of sand would be 6.02 times 10 to the 23rd grains of sand. This word changes depending on what we're dealing with. When we're dealing with donuts, it's donuts. When we're dealing with grains of sand, it's grains of sand. And the same thing kind of happens with our substances. The terminology we use depends on what we're dealing with. With covalent substances like carbon dioxide, two non-metals, covalent bond, we use the word molecules. So we would say one mole of carbon dioxide equals 6.02 times 10 to the 23rd molecules of carbon dioxide. When dealing with elements, like calcium, the word changes because elements aren't made of molecules, they're made of atoms. So we would say one mole of calcium is 6.02 times 10 to the 23rd atoms of calcium. Now this is for the monatomic elements, the ones that are single atoms. If it's a diatomic element, hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine, or iodine, we go back to molecules again. Because these diatomic ones are covalently bonded together. They are two non-metal atoms. So they are covalently bonded together, and the terminology switched back to molecules again. So if this had been hydrogen, it would say H2 here. And that 2 tells us we have two atoms bonded together, and we would change that word over to molecules again. Finally, for the ionic substances like sodium chloride, well, they don't have molecules. And figuring out the number of atoms in one of these is not the same. It's not even the same kind of conversion. There's more math you have to do with that. So we use the term formula units. So one mole of sodium chloride is 6.02 times 10 to the 23rd formula units of sodium chloride. So again, one of the things I think that makes this more difficult than the mole volume conversions is that there's a terminology thing. You have to be able to recognize that whenever you see molecules, atoms, or formula units, you're doing one of these conversions. It's a mole particle conversion. The second thing that makes it trickier is the number in scientific notation. And you either have to know how to use numbers in scientific notation mathematically, or you have to have a calculator that can do it. And then if you're using a calculator, you've got to make sure that you know how to put them in the calculator correctly and that you know how to read the calculator display correctly. So let's jump into it. Let's do a conversion here. Let's convert 7.9 moles of magnesium chloride to formula units. And again, terminology is dependent on substance. I said magnesium chloride, so I'm using formula unit with that because it's an ionic compound. Again, when the ionic compounds are involved, the term is going to be formula unit. When it's a covalent one, it'll be molecule. When it's an element, it'll be atom. So you just got to be aware. The equivalence, one mole of magnesium chloride equals 6.02 times 10 to the 23rd formula units. Now set up always the same. You always start with the number that I give you, and I have given you 7.9 moles of magnesium chloride. It's times, and then the conversion factor, it's a fraction we make from those two numbers under my equivalence. Now I have to decide what to put where to do that at a look over here. I've got moles in my given, so I'll put moles on the bottom. I take that number there, and I put it there. The other number has to go on top. It gets to where it takes up a lot of space when you don't abbreviate your units, but I make an attempt not to abbreviate those units so you know exactly what I'm working with. You don't have to worry about how I abbreviate it. If you make abbreviations for things, though, make sure that you know what they are. Don't get confused by your own abbreviations. And when you have to show your work on something like a test or a quiz, make sure your abbreviations are either obvious enough for your teacher to recognize or you've made some kind of key that says what those abbreviations are, because we'll be looking for units and unit cancellation. The moles of magnesium chloride cancel out. It's a numerator-denominator thing. We have formula units of magnesium chloride as the only thing left, which is what we were asked to find, formula units, magnesium chloride. So we know our setup's correct. Now we just got to put this thing in the calculator. Now the key is to know your calculator. My calculator has an exponential notation button, and it's right there. On this particular calculator it says times 10 to the x. But on other calculators it's different. You got to know your calculator. On the ones that I have in class, if you're going to use, the button's completely different. On this calculator, the exponential notation button is this EE key right there. On other calculators it's labeled EXP. On other calculators it's a second function. So again you got to know your calculator and how your calculator works. So you can put these numbers in it the correct way so you don't get any kind of issues when you're letting it do the math for you. That's the most common mistake I see. Students who put the numbers in their calculator, they don't understand how to put the numbers in their calculator, and they make mistakes. So let's look at how this one would actually go in the calculator. I would start by putting in the 7.9, let's type in that in, times, so hit the times button. Then I put in the first part, the 6.02. Now at this point I don't type in times 10, I hit my exponential notation key. And then I put in the exponent 23. What you see on the display right now is 6.02 times 10 to the 23rd. This calculator, however, cannot express that, it can't show that. Would you push that EE key? It means times 10. Now I push equal and this is what the calculator spits out. Now this part here is the number that goes in front of the times 10. I'm going to round this for significant figures, I'm going to write down 4.8. Again, two significant figures there, I want to limit myself to two significant figures in my answer. This, this 24, that's the exponent that goes on the times 10. Again, you've got to be able to interpret that, you've got to be able to read that from your calculator. When I punch it into this calculator it's a bit different. Again, I put the 7.9 in first. Then I hit the times button. And now I've got to put in the number in scientific notation, the 6.02 times 10 to the 23rd. So again, I put in the first part, the 6.02. Then I hit my exponential notation key and I'll note on this calculator it actually shows you the times 10. And then I hit the 23 and equals. This calculator actually gives me the number in scientific notation. So all I have to do is round it. So you've got to know how your calculator works, you've got to be able to put numbers into it in scientific notation, take numbers out of it in scientific notation if you want it to do the work for you. Do one more, the opposite conversion. Let's convert, I don't know what the deal with 7s are today, 7.8 times 10 to the 24th atoms of iron to moles. Now I used atoms this time because I've got an element there and it's not diatomic. Whenever it's just a normal element, the word I'd use for particles would be atoms. The equivalence is still the same. One mole of iron equals 6.02 times 10 to the 23rd atoms. As always I start with my given. I was given that. 7.8 times 10 to the 24th atoms of iron. Times and then the conversion factor. And again as I set that conversion factor up I know these two numbers are what go into it. I can decide to put one on top, one on bottom. I look over here for that. Atoms. I got to put that unit on the bottom. I'll put the one mole on top. Just like that. Atoms of iron cancel out. All this left is moles of iron which is what I was asked to find so I know my setup is good. So now I got to put it in the calculator. I got two numbers in scientific notation to deal with. So I start with my 7.8 times 10 to the 24th. So I hit 7.8. Exponential notation key 24. And that's what the display looks like. The 6.02 times 10 to the 23rd is on the bottom. I can ignore that one because it's on the bottom I divide by it. So I hit divided by. And now I got to put in the 6.02 times 10 to the 23rd. 6.02. Exponential notation key 23. And again the display looks like that. I hit equals and that's what it spits out. 12.9568 whatever. Two significant figures here. I'm going to put two in my answer and say 13. Now I've had students ask me this. When I'm converting it to atoms or molecules or formula units, will I get a number in scientific notation? Yes. You will get a number in scientific notation. Whenever you're trying to find formula units, molecules, or atoms, you're going to get a number in scientific notation. They ask, will I get a normal number every time I'm trying to find moles? Probably. You could get something in scientific notation if it was a very small number of moles. And the calculator wanted to give you the number .000398 in scientific notation. It could do that. But it's not going to be one of these giant 24, 22 exponents. It'll be much smaller because those numbers are much more reasonable when you're converting it to moles.