Lecture 01. Introduction to General Chemistry
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ZellwachstumOberflächenchemieTankChemieChemische ForschungVorlesung/Konferenz
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06:41
PolyurethaneMannoseBohriumMonoaminoxidaseMagnetometerDurchflussWursthülleGesundheitsstörungKonkrement <Innere Medizin>KonvertierungBaustahlTiermodellSonnenschutzmittelPeriodateGangart <Erzlagerstätte>AzokupplungPosttranslationale ÄnderungSingulettzustandTerminations-CodonBukett <Wein>SchönenSetzen <Verfahrenstechnik>Chemische FormelElektronische ZigaretteLinkerErdrutschComputeranimationVorlesung/Konferenz
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MannoseMagnetometerBohriumAuxineSingle electron transferCalciumhydroxidHydroxybuttersäure <gamma->KonvertierungSonnenschutzmittelSingulettzustandElektronische ZigaretteKonkrement <Innere Medizin>HeliumBukett <Wein>OktanzahlMannoseKrankengeschichteLaichgewässerMethylphenidatTiermodellKatalysatorComputeranimation
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NatriumhydridMannoseKaliumAtomVerhungernTiermodellBohriumInsulinkomabehandlungVancomycinCalciumhydroxidVerschleißChemische EigenschaftChemische ForschungCHARGE-AssoziationElektronische ZigaretteValenz <Chemie>BrandsilberSetzen <Verfahrenstechnik>MeeresspiegelQuerprofilAlkoholfreies GetränkOrdnungszahlDeprotonierungAzokupplungIsotretinoinChemische StrukturPhasengleichgewichtWursthülleHalbedelsteinElektron <Legierung>GradingTiermodellNeutralisation <Chemie>Konkrement <Innere Medizin>AtomSchönenKörpergewichtKernproteine
29:02
MagnetometerMannoseBohriumMagmaAdenosylmethioninMolekulargewichtsbestimmungBrandsilberWursthülleSenseKohlenstofffaserGangart <Erzlagerstätte>Chemische ForschungHope <Diamant>Aktivität <Konzentration>Computeranimation
32:20
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Chemische ForschungEthanKleine EiszeitCHARGE-AssoziationChemisches ElementCalciumhydroxidMalzMannoseChemische VerbindungenHydrazinCHARGE-AssoziationMolekülAtombindungThermoformenFunktionelle GruppeChemische FormelBukett <Wein>Organische ChemieElektron <Legierung>AluminiumAlterungMagnesiumElektronegativitätWursthülleChemische StrukturTranslation <Genetik>SauerstoffatomSchussverletzungNatriumchloridRemissionAtomIodNeutralisation <Chemie>Fluor <Medizin>KaliumiodidMethylglyoxalValenzelektronIonenbindungKaliumMetallbindungDelokalisierungValenz <Chemie>Monomolekulare ReaktionStickstoffatomComputeranimation
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CHARGE-AssoziationAtomBraunes FettgewebeInsulinMannoseNatriumhydridBohriumNatriumthiosulfatSterblichkeitEthylen-Vinylacetat-CopolymereBleierzCHARGE-AssoziationEisenOxidschichtQuellgebietNatriumchloridThermoformenFunktionelle GruppeValenz <Chemie>AtomChemische ForschungSauerstoffatomElektronische ZigaretteSulfateCarbonateChemische VerbindungenPhosphateSammler <Technik>KonservendoseElektron <Legierung>OxidationszahlSulfideBukett <Wein>PhosphideSetzen <Verfahrenstechnik>SäureOxideChemisches ElementSonnenschutzmittelSymptomatologieÜbergangsmetallValenzelektronKrankengeschichteGezeitenstromNatriumWasserTechnikumsanlageReplikationsursprungSubstrat <Boden>ZuchtzielQuarz <alpha->QuerprofilPegel <Hydrologie>Memory-EffektFeuerSenseComputeranimation
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Sammler <Technik>Elektronische Zigarette
Transkript: English(automatisch erzeugt)
00:07
All right, welcome to Chem 1A. So this is the first class in the general chemistry series here. So we're going to go over, we're going to start with just some general introduction to the course and some fundamentals. And these are the things that you're sort of already
00:20
expected to know when you walk into the class. We have a bunch of homework on that set up for you so that you can go through and you can learn everything you need to know about it. In the meantime, I'm going to cover some of the important aspects of it today and maybe next class. So over the course of the class, we're going to cover the first four chapters in your book, in the Atkins book.
00:41
So we'll start off just a cursory overview of the fundamentals, things that you would have learned in high school or Chem 1P. And we'll go over that in just skimming the surface of it and let you take care of most of that at home. Then we'll start into chapter one. And this talks about quantum mechanics and atoms at the very, very basic level.
01:01
And we'll do lots of material on that and spend pretty much the first four weeks or so on that. Your first midterm will cover just chapter one. From there we'll move on and we'll start building molecules out of these. And we'll go into a little bit more complicated structures, we'll learn about geometry, and we'll learn about all of the ways that these look
01:22
and interact and how they form bonds in more detail rather than just saying that they bond together. From that point, we'll also learn how they interact with each other, how one molecule can interact with another molecule, and the way in which these can change based on the different properties of the molecules.
01:40
And that'll be what your second midterm is on. At that point we move on to chapter four, which we start learning about these in bulk properties. So we'll start learning about gases and how gases interact with each other. And we'll do that for the final. So for the entire fundamentals section, this is the thing that you already sort of know,
02:03
and I say that theoretically, because it's probably back there somewhere from three years ago when you took high school chemistry in 10th grade. So go back and review it all. That's A through M in your book. For J, K, and L, we're not gonna really talk about that at all. I gave you a little bit of homework on it. That's gonna be really important for 1C.
02:21
And if you have me for 1C, I'll test you on that when we get there. For this class, I'm not gonna test you on that at all, and I'm not gonna talk about it at all. But everything up in through J is your responsibility and is what we'll sort of go over in class today. So with all that in mind, let's start in on this.
02:41
We're gonna start with significant figures. This is really important and sometimes gets forgotten about. And this is a way that we measure how precise we can be in any of our calculations. So for every calculation you do in this class, you're going to have to worry about significant figures. So there's a few different rules for this.
03:01
The first one is sort of nice. Anytime you have a non-zero number, this is gonna be a significant figure. So in every calculation you do, you're gonna count up all your significant figures and you're gonna decide how accurate you can be. So for instance, with this one, it says 54. We have two significant figures. And what that means is that we can be accurate to this 54 place, or to this one's place right here.
03:25
Now when we get to zeros, that's when things start to get a little bit more complicated. So first we're just gonna talk about what is and isn't a significant figure. Then we'll go on to how to calculate with them. So if you have a zero that's between two other digits, so for instance this zero,
03:41
where you have a zero in between a five and a four, that's gonna also be significant. So in this case where we have 504, the five and the four are significant, as well as the zero that's between them. Now, if we have zeros that are left of the first non-zero digit,
04:01
so I have some examples here. We have 0.00504, something that you'd see pretty regularly, you know, a decimal point. And then this one, which is a little bit more strange and not something that you would ever see really written out, but just in case I've included it. In this case, we don't count either of these zeros. These zeros, I think we can kind of see
04:21
why they're not significant. These, they're just placeholders. We can't write .504 and have it be the same number as .00504, they're simply placeholders, so they're not significant. Now, if you have numbers that are greater than one, and you have zeros that are to the right
04:41
of the decimal place, those are definitely significant. If you think about it, you can think about this without actually memorizing the rule. Could we just write two? Well, sure, of course we could just write two. That wouldn't change the number at all. So there's no reason to include this .0000
05:00
unless you're doing it for the sake, unless you're doing it for the sake of showing how precise you can be. That you can not only just gauge to this one place, but you can go all the way out to here. And so those are all gonna be significant. Now, when you compare that to up here,
05:21
remember I said you can't just write .504, that changes the number. So here, these are placeholders. Here, these show precision. Now, this next part says trailing zeros aren't significant unless the decimal point or scientific notation is used. So for instance here, I just have 4,200.
05:42
There's no decimal point after. Those two zeros aren't significant. And that's because you can't just write 42 there and have it be the same number. Those zeros are just placeholders. Anytime you have a zero that's a placeholder, it's not gonna be significant. Anytime you have a zero that isn't a placeholder, like for instance here, those are.
06:01
Now, what if we wanted all of these digits to be significant? We can force them to all be significant by putting a period at the end. So if we just put a period at the end or a decimal point at the end, then that forces, that tells whoever's looking at your work that you really can measure out to the ones place. It just happens to be that in this case, both the 10 and the ones place is zero.
06:23
Now, what if we wanted just 42 and we wanted that first zero to be significant? There's a way to do that too. Scientific notation is the way to say exactly what you want to be significant and what you don't. So in this case, we can write out 4.20 and that says, hey, everything that we have written
06:41
in this scientific notation, that's significant. So if you have it and you have it written out in scientific notation, whatever is there is going to be significant. So if you ever get to an exam and it rounds up to something like 4,200 and you say, but I need three significant figures, how can I write that down? How can I get that point on the test? Well, it's going to be by going through
07:01
and putting it into scientific notation so that I know that you know that it's three significant figures. Now, the next part of this is how do you do calculations with this? Because just being able to count how many significant figures you have is great and for something like taking a measurement, that would be fine.
07:21
But you also, you're going to be doing actual calculations. You're going to be plugging things into equations, maybe something that has three significant figures and something that has four significant figures and you need to know how many come out at the end. So there's two different sets of rules. There's rules for if you're doing addition and subtraction and there's rules for if you're doing multiplication and division.
07:40
So for addition and subtraction, you use the lowest number of places or decimal points. So you're not actually going to be counting significant figures, as we've just talked about on the previous slide, for addition and subtraction. So for example, let's say we're adding up .24, so something with a ones place and a tens place and something like .345,
08:03
where you have up to the thousandths place. You round this to the lowest number of decimal places. So in this case, two decimal points or two decimal places. And so you would round it to .59. You're not counting significant figures here, you're counting decimal places.
08:23
So what if you don't have a decimal? What if you're just sitting in the higher numbers? Well, in that case, you'd just round to the number of places. So here we're all the way out to the ones, but here we're only at the hundredths. So when you round this, you round to the nearest hundredth. And so you end up with 4,500.
08:43
So that's for addition and subtraction. You're not counting sig figs, just places, whether that be decimal places or places to the left of the decimal point. With multiplication and division, that's where you're going to bring in all that significant figures that we did in the previous slide.
09:01
So for multiplication and division, you go to the lowest number of sig figs. So if we look at 23, we can see that there are two significant figures. If we look at 436, we can see that there are three significant figures. So when we want to round this, we want to round to two significant figures.
09:20
Now if you go ahead and plug this into your calculator for me real quick, you'll see that when it rounds, we end up with a one and a zero, and we can't, and you might say, well, how do I round that? Can I just put, you know, 10,000? Well, you can't just put 10,000 because that would then have just one decimal, or just one place, one significant figure, and you need to have two.
09:40
So you would say, okay, well, now I have to convert it into scientific notation so that I can put the point zero there. So let's do another one with division. So here we have 453 divided by 3.2. So sure, we have a decimal place here, but that doesn't make any difference. We don't have to pay any attention to the decimals.
10:00
We just go through and count how many sig figs do we have. So here we have three, and here we have two. So when we get all done with that, that means that we're gonna have two significant figures. And so we're left with 140. Now, some rules for how to actually work with these. So these are the rules for coming up with an answer
10:20
that you're gonna turn in. And that's fine if you only have one or one step. You can just say, okay, well, I've added these two numbers, I've multiplied these two numbers, whichever, and go ahead and put it down on the paper. But if you have five or six different steps, you're taking an answer from one equation, filling in another equation, now you have to kind of keep track of this. It is not a good idea to round it every single step.
10:43
That introduces a little bit of an error every single time. And there's a good chance that you'll start getting answers wrong, especially on sort of online systematic homework. So what you wanna do is you wanna hold out a few decimal points. To be honest, when I do these sorts of things, I just keep them in my calculator and second answer the whole way through.
11:01
If you wanna write them out, that's fine too. Just write out a couple points past the significant figure, the last significant figure. Then you might say, okay, well, how am I supposed to keep track of what's going on then? How can I, if I take the answer from one equation and I add all these extra sig figs, how do I know how many sig figs I have there? Just put a little underline under the last significant one. And then you'll see this when I start doing some work,
11:22
but every time I get done with an answer that I need to use someplace else, I put a little underline under the last significant figure so I can keep track of it. So that's some kind of hints for actually going about doing this and, you know, real problems. Okay, so that's one of the most basic things that you're gonna have to know to do every single calculation problem in this class.
11:43
Now, the next set of things that you really need to have a good background on is something called dimensional analysis or conversion factors. And these two are sort of very much interrelated to each other. The idea with a conversion factor is you have something that says this much is equal to this much of something else.
12:01
So 100 centimeters equals one meter. That's a conversion factor. Now, the way we use this is through something called dimensional analysis. It's one of the main ways anyways, where you can go through and you can convert one item into something else using conversion factors. The easiest way to do this is to actually go through and do a few example problems.
12:22
And so that's what we're gonna do. All right, so we have your worksheet that you've printed off from the internet.
12:42
And we start out by saying the average speed of helium at 25 degrees is 1255 meters per second. And I say convert that to miles per hour. So the way that you wanna always think about conversion factors is writing down what we have and writing down what we're trying to get to and seeing what you need to do in between.
13:00
So we'll start by writing down what we have. So we know we have this. And we know at the end of the day we need to have miles per hour. How do we get between them? Using only conversions that we know or can easily look up.
13:24
I ask you to memorize all of the metric conversions. I don't care about the other conversions. I would give them to you, the metric ones you have to know. So if we have meters on top, we need to do something to get rid of meters. Having something in the numerator is saying that you're multiplying it. So the opposite of multiplication is division.
13:42
So we put that on the bottom. And we know that we can get from meters to miles through using some sort of conversion factor that we either look up or have memorized, more likely look up. And so we'll put miles up here. Now we go and we find that conversion factor and we say, well, for every one mile,
14:05
there's 1,609.3 meters. When you look up these sorts of conversion factors that aren't nice round numbers, it's not something like in the metric system where you have one in 10 and 100 and 1,000. You want to keep one place more,
14:23
or one significant figure more than what your actual number that you're starting with is. So if we think about how this cancels, we now would have miles per second if we keep track of all of our units. We don't want miles per second. We want miles per hour. So now we have seconds on the bottom
14:42
and we want to get rid of that. So that means we have to put seconds on the tops to cross that out. And we want hours on the bottom. So we'll do this. And then we fill in this conversion factor. Of course, this would be one that you'd be expected to know.
15:01
And if you didn't remember that off the top of your head, you know how many seconds are in a minute, so you could convert to minutes, and you know how many minutes is in an hour, so you can convert to hours. From this point, now we can look and we can see that our meters cancel. And we can see that our seconds cancel. And we can see that we have miles per hour.
15:22
So our units are all set, which means our answer is going to be fine. And we can do 2807. So you can see that that's much easier to figure out how to do than to try to memorize, well, am I multiplying by this conversion factor? Am I dividing by this conversion factor? What am I doing? So this way you can just trace your units around.
15:43
Okay, we have one more of these to do. Say, how many minutes does it take light from the sun to reach Earth, given that the distance from the sun is 93 million miles and the speed of light is three times 10 to the meters per second? Or three times eight meters per second.
16:01
Okay, so to do this one, now this one I'm kind of asking you a real question, but it really turns out to just be a bunch of conversion factors put together. If we know that we have a certain amount of miles, and it's 93 million, which means it's 93 times 10 to the sixth. And now at the end of this, we want to get to time.
16:27
So we need to trace through all the conversion factors that we can find in order to get this. Well, we can start by saying we have miles here and we know our speed is in meters per second. So we have a distance here and we have a time.
16:42
That's going to be a good way that we can go through and try to get to time. But it's not going to work with miles. So let's change miles into meters and we're going to do that the same way that we did here. Now, notice on the second problem though,
17:00
if you look back to your first one, the ordering is flip-flopped. And that's because we're converting from miles to meters instead of from meters to miles. So we can write in those numbers and you can also hold off and write in all the numbers at the very end too.
17:23
So now we know that we have meters on top and our miles cancel out and we can look at what else we can do. We want to get from a distance to a time so we need something that has both distance and time in it. Now, from there we need to decide well are we going to multiply by this number
17:41
or are we going to divide? So again, we trace through our units. We have meters on top and we don't want meters so we divide by it. So that leaves us with seconds on top which is what we want because that'll end up with our time unit. So now we fill in our numbers. The number here goes with the meters
18:01
because it's on top. So 3.00 times 10 to the eighth and we put one second here. Now at this point we want to look
18:22
at what I had asked you for. So we could do this in seconds if we wanted but I had actually asked for minutes. And so at this point we can see well we have seconds so we need to convert that into minutes. And we know that we have 60 seconds in one minute
18:43
so that gets rid of this unit leaving us with minutes which is what we wanted and we can solve for that.
19:01
Now it's time to take a look at our significant figures here for both of these. Come both up. Now notice on this one I left it as four significant figures. Now I need to go back and say okay, for all of these calculations did we do this right?
19:20
We started with four significant figures here. We divided by five here and we did that on purpose, right? We looked up that number and we said okay, well we have four significant figures here I need to keep one extra. Now what about this one? That 3,600. Does that mean that we should round to 28
19:42
or 28,00? Well no. Whenever you have a definition you don't round to that. So there is exactly 60 seconds in one minute. There is exactly 60 minutes in one hour. There is exactly 3,600 seconds in one hour. It's defined that way. And so you can think of it as being
20:00
infinite significant figures. However many you need there to be. So that means that this is gonna be left as four because we started with four. Now when we come down here we started with two here. We again looked this up. I put it as five basically just because I had that number handy.
20:20
But you could have rounded it to three if you had wanted. We have this number which has three significant figures. And then we have this one which looks like one but remember it's a definition. And so because of the definition it's actually infinite. And so the only thing that matters for our significant figures is the 93. So we have two significant figures here
20:42
and so we need to have two significant figures here. Okay, so that sort of walks us through
21:05
some of the calculations that we're going to be doing in a very general format where you don't need to have a lot of chemistry background yet. You can always use dimensional analysis and looking at the units and crossing off the units as a double check whenever you go to do anything.
21:23
So every problem that you do you should write out all of the units all of the time and then each time go through and look at where they are and look at how they cancel and make sure that at the end you have a unit that makes sense. If you're measuring distance and you come out with a unit of time you did something wrong. If you're measuring velocity
21:41
and at the end you need to have a velocity and you come out with something like meters and no second per second you did something wrong. So this is a great way to go through and make sure that you did everything okay. We'll get to times later on in the quarter where we have a constant that has tons of different types of ways of writing it in and all of the differences are with units.
22:01
How do you know which one to use? You can memorize it and you can say well when I use this equation I'm gonna use this version. When I use this equation I'm gonna use this version. Or you can just look at the units and say okay I know I have liters and atmospheres so I'm gonna use this version of R. Or I know that I have joules so I'm gonna use this version of R. Things of that sort.
22:24
So now we're gonna get into the structure of an atom and we're gonna do this at a really basic level right now and then chapter one we'll get into it in much much greater detail and in some ways I'll tell you that we lied a little bit here. So this is the Bohr model of an atom and I like to sometimes call this the high school model.
22:42
This is sort of the first model that we teach you. It has some very good uses, some of which we're gonna take advantage of if you're starting this class you're next. But it also isn't 100% accurate but it's a good starting point. So we'll kind of start from there here. You can think of it as being a nucleus in the middle
23:01
that has two different parts of it. It has protons and it has neutrons. The protons have a positive charge. The neutrons have no charge at all. And then around this nuclei, and right now we'll think of it as rings and later on we'll expand that a bit. We have electrons
23:21
and those electrons are negatively charged. So there's some things you wanna be able to look at a periodic table and calculate pretty quickly without having to put a huge amount of thought into. So if you don't know how to do this, it's fine but you wanna go get some practice at it. So if you have the number of protons you have and you subtract the amount of electrons,
23:42
your protons have a plus one charge, your electrons have a minus one charge. So that's gonna give you the charge of the ion. Now in any sort of neutral compound, this atom, that's zero because you're gonna have the same number of protons as electrons. But you can also start adding and subtracting protons and electrons as time goes on
24:03
and making ions out of them. And we'll talk about that in much more detail too. So keep this in mind, that your charge is always gonna be equal to your protons minus your electrons. Now, if you look at your periodic table, there's a bunch of different numbers that you can deal with.
24:21
One of them is your atomic number, that's your number of protons. And then there's also an atomic mass. An atomic mass is your number of protons plus your number of neutrons. And so you can take those and you can add them up and that gives you your atomic mass. Because you'll always have a periodic table, you'll always know your number of protons,
24:41
you'll always know your atomic mass for any sort of exam or anything like that. And what you'll see is a lot of times we can back calculate and figure out how many neutrons we have. We can take your mass and subtract your protons and get your neutrons. And we'll do that a lot in 1C when we start getting into nuclear chem.
25:00
Now, you really have to remember these charges, which ones are positive and which ones are negative. And in order to help remember that, we have a little joke, lots of great and simultaneously horrible chemistry jokes out there. This is one of them. So you have two neutrons and they walk into a bar and they order a couple of drinks.
25:22
As the one is about to leave, the waiter says, how much does it cost? And the neutron, let me start over. Okay, a neutron walks into a bar, orders a couple of drinks. As she's about to leave, she asks the waiter, how much? And the waiter replies, for you, no charge. So that's the joke to sort of remember what a neutron is.
25:41
We have another one here and this one is one of the most famous one that gets repeated over and over and over again. And you have these two different atoms and they're talking to each other and the one says, I'm hit, I'm hit, I've lost an electron. And the other one says, are you sure? And the first one says, I'm positive. They lost an electron and so they're positive, right?
26:00
So two nice horrible jokes for you to remember these by. We'll have lots more of these as the quarter goes on. Okay, so now comes some sort of time for just general definitions. So first of all, we have something called an isotope. What is an isotope? So anytime that you have the same number of protons,
26:24
but you have a different molecular mass, that's an isotope. And the reason why you get this is because you have different numbers of neutrons. And so your neutrons within one particular atom can change and without really changing too much of the properties. We'll see again in 1C
26:41
that some of the properties definitely change. The mass definitely changes because you're adding in a neutron, which has a mass of about one. But most of its properties are very similar. Now, why are the molecular masses of the periodic table decimal points? So you should probably always have a periodic table handy
27:00
in this class, just kind of sitting out. Starting next class, you probably want to do that. There's, you know, they're around. So whenever you look at this, you'll see that your molecular masses are decimal points. And why is that? Well, the reason for that is that they're actually going to be an average.
27:23
They're going to be an average of both or all of the isotopes of that compound or that atom. So something like silver has two isotopes that make it up. So sometimes you'll get a silver 107. If you were to weigh the mass of that one atom, you'd come out with a unit of 107.
27:42
Sometimes it's 109. So on the periodic table, what they do is they do something called a weighted average. And, you know, weighted averages are a good thing to know how to do. If you don't know how to do that, review it in your math class. It's also how your grades are figured out, you know. So when you go to figure out your grades and I say figure out a weighted average, that's what I'm talking about.
28:01
And that's how it's determined here. So in this case, we would have 107 silver making up 51%, 109 silver making up the rest. We'll do this out on the document camera in just a minute. You'll notice some of these are even more complicated.
28:21
Some of these will end up with two or three different isotopes. Now, the reason we do a weighted average, as opposed to just averaging it, you may say, why can't I just take this and say, well, 107 plus 109 divided by two? Well, we want to know what the mass of this is as we go out into the world and we take some silver out of the, you know, some silver out of the ground, clean it up,
28:40
get rid of all the ore and purify it. How much is that silver? What's the molecular mass of that silver? And not all of the silver is split 50-50, 107 and 109. And this is where the idea of weighted averages come in. So we'll do this one out on the document camera
29:11
so that we can see it all worked out. Okay, so we have 51.839% of silver is 107. So we need to figure out how much there is of each.
29:21
So we know this because the problem says so. Now we also need to know what percent is 109. Well, it's the rest of it. So we just take 100, subtract that.
29:42
So this is 100 minus the silver 107%, which gives us the 48.161. Now we do what we call a weighted average. So I'm gonna do it out in two steps. You can do it out in one. It's, you find either way. So if we know that we have 107 grams of this,
30:04
we can just say that we have 107 grams per mole and 109 of this. What we'll do is we'll go through and we'll multiply that by the percent.
30:23
And the same thing here. So we've taken 107, multiplied it by the percent that makes it up in nature. This multiplied by the percent that makes it up in nature.
30:49
And we get those two numbers and then we add them up and we get that.
31:02
Now with everything in chemistry, you wanna be thinking, does this make any sense? Now, in this case, we have a weighted average between two things. It's 107 and 109, and it's about 50-50, right? One's 51, one's 48, it's about 50-50. So we would expect the answer to be close to what the normal average would be
31:21
or what the real average is, which is 108. So since we have this and this being added together at almost equal proportions, we want it to be close to 108 with a little bit less because the 107, the lower number, has a little bit higher percentage. And that's exactly what we see.
31:41
We see that it's close to 108, just a little bit less than 108. So that makes sense based on the averages and what we know about how averages work. And so that's it. Now, this was a case where we only had two ISIS hopes that we were averaging. You could do this for more. Something like carbon has one main one and then two smaller ones.
32:01
You could do that for each. And you would just do this three times and then add it all up.
32:30
So now that we know all these things about atoms, we know they're protons, we know they're electrons, we know they're neutrons, they're masses, we need a nice way of looking at all this data and figuring things out very quickly.
32:41
And this is where the periodic table comes in. We have all the elements arranged in order of increasing atomic number. So atomic number, remember, that's the number of protons that we have. Now, they're arranged in these repeating patterns. And we'll get into more detail about exactly how that is. But for right now, what you can know
33:01
is that they have the same number of what we call valence electrons, outside shells. If you think about the Bohr model, you can kind of think about those rings, right, and whether they're filled or how many they have in those outside rings. And so what happens there is that gives certain columns or groups similar properties.
33:20
So everything that's going to be in group one is gonna have a relatively similar property to each other. Now, of course, there's going to be differences because the atomic mass here is much, much bigger than here. The number of protons, the number of electrons are much bigger. And there's some trends that we'll be able to pull out of the periodic table later on. But for the most part,
33:40
this group would have the same sort of properties as each other. This group's same sort of properties as each other, all the way across the periodic table. So if you go down a column, you have very similar properties. Now, this happens to be my sort of favorite periodic table that I carry around and have on all my books.
34:01
I actually replace a lot of my book periodic tables with this one. You know, find your favorite periodic table from the internet, print it out, and keep it with you all the time in class and when you're doing chemistry. You don't really expect you going to the bars with them and such things. But keep them around you whenever you're doing your homework. Keep them out in class with you because I'll refer to them a lot.
34:23
Okay, now comes something that we're gonna get into a little bit with naming. And this is probably all of the freshmen chemistry students' least favorite part about this class because there's a lot of memorization. In general, I say with chemistry, you shouldn't be memorizing hardly anything.
34:40
If you're memorizing things, you aren't in general or not learning them. And in chemistry, that gets dangerous. If you memorize how to do a problem, you're probably gonna have problems on an exam because I'm gonna give you one that's a little bit different. And if you don't really know what you're doing, you're not gonna be able to solve it because it's not gonna be the exact same as your homework problems. This is sort of the exception to that.
35:02
You have to do a lot and a lot of memorization for the ionic naming. It's a pain, just do it. You're gonna need it for 1B, you're gonna need it for 1C, and you just need it to be around chemistry in general, which includes the biology that you're gonna be in. You want to have a good idea of what's happening and you wanna be able to look at a compound
35:21
and name it quickly without having to think about it too much. I can test you on this in the first midterm just by saying, here's a name, give me the formula, here's the formula, give me the name. I can do it on the second midterm by saying, draw me this compound and if you don't know how to name it, you don't know how to pull the formula out of the name I gave you, you won't be able to do it. So, make sure you just go through
35:42
and do all of this. So, before we can get into naming too much, we have to figure out, how do we know what type of naming we're gonna do? So, up here I have, we have ionic, molecular, acids, and organic.
36:00
Now, we're gonna get very much into ionic, molecular, and acids. Those are the ones that you're testable on in this course. For organic, you have a homework assignment on this. We'll talk about it a little bit. Don't worry about it too much. In general, that's all gonna be covered in really great detail next year, but you should have a general idea of how it works
36:20
because I'm gonna talk about it. I'm gonna say things like methane and ethane and, you know, ethanol and propanol and you should have some idea of what I'm talking about. I'll also always have the structure up there, but you don't want something like that that to throw you off. And so, just have a general idea of how it works. Be able to answer questions on it if you have the book in front of you.
36:40
We're just not gonna get too into it this, or this class. That'll be more for next year. These three are the ones we're gonna focus on. Now, all of these are gonna be named very differently. If you have an ionic compound, it's named completely differently than a molecular compound. You'll learn to like the molecular ones for the naming purposes here. And acids are gonna be sort of based off
37:01
the ionic nomenclature, but it's still very different. And so, before we can actually get into the rules for naming, we have to get into how we know which one is which type of compound. So, to do this, we have to talk a little bit about bonding and how things bond. So, whenever something is trying to bond
37:21
with another atom, it's trying to do what we call complete an octet. Now, we'll see some atoms don't actually do that exactly, but they're trying to. They're trying to get a full octet, which means that they would have eight electrons in their outside shell. So, if you have one atom that has six in its outside shell,
37:40
and another one that has six in its outside shell, it can go and it can form a bond. Now, in this case, it's gonna wanna share those electrons because you have six here and six here, so this one can't just give two of it away or it's going to have some problems. This one can't just give two of them away or it's gonna have some problems. There are times when you can do that,
38:00
when you can just trade electrons, and there's times when you have to share electrons. And that's your difference between your two different types of compounds, or your two different types of bonds. So, for ionic compounds that have ionic bonds, they're gonna trade electrons. One atom is going to give away its electrons to the other one. So, something like sodium chloride.
38:22
So, if you take and you look at your periodic table a minute, and you look at sodium right here, and you look at chloride right here, you can see that sodium has one electron in its outside shell. And the periodic table is really nice for looking at this quickly, because you can look here and say,
38:41
okay, this has one valence electron, this has two valence electrons, three, four, five, six, seven, and eight, all the way across. So, we can use this to look and see how many valence electrons we have very quickly. So, sodium has one, and chlorine has seven. So, they can just trade electrons. The sodium will say, well,
39:00
I don't really want this one electron sitting there by itself. You take it, it gives it to the chlorine, and the chlorine says, great, this gives me eight. So, now they both have eight. In covalence bonding, they're sharing the electrons. So, this would be something like carbon and oxygen, or two oxygens, or two fluorines,
39:20
where they don't, they can't just give them away. They'd still be too short of electrons. And so, instead, they'll share them. Carbon will let oxygen take some of them. Oxygen will, you know, do some of them. And then, you count those electrons for both. We won't get too into metallic bonding, but it is important to talk about
39:40
and have sort of in the background. Now, in metallic bonding, you have these big networks, and these big networks of electrons that can move back and forth between all of them. Here and here, you sort of have the electrons that are relatively associated with one or two groups. Here, they're completely delocalized,
40:01
which means that you can kind of move them from one side to the other if you do the right sort of thing to it. And we call this, you know, a wire, right? We can take a wire and we can stretch it out. That's all metallic bonds. We can put electricity through it. And the fact that you have these delocalized electrons that are going across this entire group is what allows that to happen.
40:22
And those are for metallic bonds. But these are the two we'll be focusing on for the sake of naming. Okay. And one last thing we need to talk about here is something called empirical versus molecular formula.
40:46
Now, this comes up in covalent bonding, not in ionic. So keep that in mind. You may even want to write that down. This is just for covalent issues. With ionic compounds, we're always going to list them
41:00
as the lowest whole number ratio. So we would never say Mg2O2, or Na2Cl2. We always want to reduce them down to the lowest amount. With covalent bonding, that's not necessarily how things work. Something like hydrazine, if you look at this, we have N2H4. And you could say, well, can I reduce that down to NH2?
41:23
Well, you can't because it changes the whole compound. N2H4 is not the same thing as NH2. So we have to have some nomenclature for this that we're going to refer to from time to time. So we have an empirical formula, which is our lowest whole number ratio. Doesn't actually tell us a lot about the molecule itself,
41:42
but it does tell us how many of each atom are in the substance. And then what the molecular formula is going to tell us is it's going to go through and say, well, this is what the molecule actually has in it. One molecule of hydrazine actually has two nitrogens and four hydrogens, or ethane, two carbons, and six hydrogens.
42:02
Now, we'll do some examples using this where you can see that we can find the empirical formula fairly easily experimentally, and we can find the molecular mass fairly easily experimentally, which is why one of the reasons that this is so important to have these differences here.
42:22
So that goes into a little bit more of covalent bonding definitions. Now we'll spend some time on ionic bonds, and then we'll learn how to actually name them. So, this is the day filled with bad jokes, so we have another one. So, the way that ionic bonding works
42:41
is by the fact that these atoms will trade electrons, and when you trade electrons, electrons have a negative charge, and so there's going to be a charge development if you trade electrons like that. So, we have this teacher up here, and you have these little atoms here, all these positive ions, says, perhaps one of you gentlemen
43:00
wouldn't mind telling me just what it is outside this window that you find so attractive. So, remember, positives and negatives are always going to attract each other, right? So, if you take an electron, you take it away from one atom, you make it a positive charge. You're taking a negative charge away, you're making it a positive charge. You're giving it to another atom, which means that that atom is going to be a negative.
43:22
So, you have a positive atom now and a negative atom, those two are going to attract just like a magnet would. And that's how you form your ionic bonds. So, how do we actually write this out quickly? Well, we do this, we can do this this way, where we have ionic bonding here. We take something like potassium,
43:40
and if you look at your periodic table, you'll see that potassium has one electron. It's in that first group, and so it has one valence electron. If you look at iodine, so you're looking at your periodic table, you're finding it on the periodic table, you see iodine's in the seventh group. So, that means it has seven electrons. So, how can we get this so they both have a full octet?
44:02
Well, we'll take the electron away from potassium, we'll give it to iodine. When we do that, potassium develops a plus charge. You've given away one of its electrons. Iodine has developed a negative charge because you've given it two iodine, and so you get this structure where you form the positive and the minus,
44:21
they attract, and they form potassium iodide. The exact same thing can happen where now, instead, you have to give one electron away to two different atoms. So, if you're trying to combine something like magnesium along with something like fluorine, now you have an issue where you have two electrons in magnesium outside shell, and fluorine only can take one.
44:42
Well, you just take double the amount of fluorines. So, now magnesium says, okay, I'm going to give you one electron, I'm going to give you one electron. Both of the fluorines develop a negative one charge, the magnesium gets a plus two charge, and they all attract each other, and they form this structure, which means that then you would have MgF2,
45:01
one Mg and two fluorines. Now, that's how you want to know what's going on, how these are trading, whether they just trade one and become K plus and I minus in this case, or sodium chloride would be the same form, or whether you have MgF2. It's all about the charges
45:20
and making sure that the charges balance. Now, there's quicker ways of doing this though, than trying to write this out each time and think about exactly where the electrons are moving around each time. So, here's a helpful trick to remember it. So, you can kind of take the charges and you crisscross them. Now, you might be saying,
45:40
how do I know what the charges are? Basically, through memorization, and we'll get into that in just a moment. So, if you write down the charges here, and the charges here, and you know that your ions have these charges, you can crisscross them down. You can say, well, I'm going to criss, I'm going to move this down to the oxygen, I'm going to move this down to the aluminum.
46:02
Now, what that ends up doing, is it gives you a compound where your charge is balanced. You can say, okay, aluminum has a plus three charge, and I'm going to multiply it by two. Now, that means I have plus six. Oxygen has a minus two charge, and that, but there's three of them. So, minus two times three, that's minus six.
46:20
So, now, you add up your plus charges, and your minus charges, and they need to equal zero. And in this case, you see that they do. So, this is sort of a helpful trick for getting you to this neutral compound faster. You want your ionic compounds to be neutral. There is one major caveat to this, though, that you have to watch out for, if you're going to use this little quick trick.
46:42
And that is that goes back to this idea of empirical formula, and molecular formula, and how that's only true in covalent. We only deal with that in covalent. Ionics always need to be the lowest whole number ratio. What if you have something that had the same charge, and it isn't one? Or, same magnitude of charge, I should say,
47:00
and it isn't one. Something like magnesium that has a plus two, oxygen that has a minus two. You crisscross them down, you form Mg2O2. That's an ionic compound. You have to have the lowest whole number ratio. So, this isn't okay. So, you need to then reduce down to the lowest whole number ratio. So, when you reduce that down, it becomes MgO.
47:23
So, at that, so whenever you have this sort of situation, and you're, you could probably just say, okay, well these are the same charge, so I'm going to say that that's just MgO. But if you didn't catch that right away, you did do the crisscross trick, and you saw that this is Mg2O2, you have to reduce that down.
47:43
Now, something that we are going to just sort of show you and then move on with, is that these form these big crystal lattices. In 1B, when you first start 1B, this is what you're going to start with, and you're going to learn all about these different shapes and these different forms, and you'll put names to them and all of that. And for this class,
48:00
I just want you to know that this exists. That when you get these, you don't have one sodium chloride. It just stuck together, and you have this one little atom of sodium chloride all by itself. What you actually have is you have these crystals. If you go to your pantry and you pull out salts, you actually have all these little crystal lattices inside of it, and that's what's forming.
48:20
So just keep that in the back of your head that this is what these ionic compounds look like. Okay. Now, how do you know what the ions are? So I've said that it's memorization. That wasn't really 100% true. So you can look at the periodic table, and you can find out what the charges are
48:40
for the most part. There's some exceptions here, but for the most part. So if you look at this first row, you have one valence electron, and you wanna find a way to get rid of that. So you can go through, and you can just take that one electron off, giving it a plus one charge. Or you can take two electrons off from this group,
49:02
giving it a plus two charge. This group, you would have three valence electrons, so you take three off. When you start getting into this group, now, it's not really gonna be able to just gain two or lose, or excuse me, gain four or lose four as easily. So those aren't gonna be big on forming ionic compounds at all.
49:21
When we're to the right side of the periodic table, we look at here, how many valence electrons does that have? Well, it has seven. What's gonna be easier? Taking away seven electrons or just adding in one? Well, of course, adding in one would be easier. And so because of that, you're adding in an electron, you're adding in a negative charge,
49:41
and so it's gonna be a negative one. If you look at this row, you have six valence electrons. It's in group six, so you have six. Is it gonna be easier to pull off six or add in two? It's gonna be easier to add in two, and so you get a negative two charge. Same thing here, easier to pull off five or add in three? Well, add in three,
50:00
so that's gonna be a negative three charge. This section in here, your transition metal's in this little group right here. For right now, you pretty much just have to memorize them. After we start talking about electron configurations in more detail and how to go about dealing with those and seeing where electrons are removed from,
50:20
we'll actually be able to explain most of them. However, for right this moment, there's really no way to explain it easily, so these groups you just have to sort of memorize. And when we get into the very end of chapter one, we'll learn why all of those are. Now, I do wanna help you memorize one of this section,
50:44
so this little group right here, we're gonna sort of pull out, and we're gonna look at in more detail. So there's something called the inert pair effect, and I don't wanna go into exactly why this is at the moment. If you've had a lot of chemistry
51:00
and you want me to explain it, I can do that later, but for now, we're just gonna leave it as this is how it works, and then at the very end of chapter one, we'll go back and we'll explain it using electron configurations. So for right now, you can notice though, that these have these groups of one, three, two, four, three, five, so they're always off by two.
51:21
You can form this top lower ion, or you can form this bottom ion, and they're always off by a factor of two. So use this to help you remember it for right now, and we'll explain why it is later on. Now we'll finally be able to get into naming these.
51:43
So for here, a lot of these listed, and there's copies of all of these sorts of things online. This is from a different book, but we've pulled out all of the ions and put them online for you. So the idea to get out of this and the lists online, is that there's also all of these polyatomic ions
52:03
that we need to talk about. Those for the most part are going to be memorization, but there's some hints for memorization. So everything that I'm about to say, we've also put into an online study guide that is available, so that you can kind of go through and see
52:20
what I'm saying when I say eights and eights, because it's a little bit hard to hear. So these are lists of things that you effectively need to have memorized, but there's tricks to memorizing it that will make life a lot easier. So there's these different types of endings and these different types of prefixes. So you have eights, eights, and eights as your endings.
52:44
If you have something with an eight ending, that is just the atom on its own, something like phosphide or sulfide or oxide. If you have something with an eight or an eight ending, like this, that's going to be your oxygens.
53:00
So something like phosphate or phosphite are going to have oxygens on the end. And the eights and the eights refers to how many oxygens or its oxidation numbers. So what we'll do here is whenever you have, you should memorize one version of these. You memorize all of the eights or you memorize all of the eights.
53:20
You don't memorize both. If you have something with an eights ending, that's what I happened to memorize when I did this back in high school or college. And I memorized through and I memorized phosphate and carbonate and sulfate. And then I knew that every time that I exchanged that to an eight ending, I just took away an oxygen. So if phosphate is PO4 three minus,
53:43
phosphite is PO3 three minus. Okay? So that's kind of your hints for doing this. Now, you'll also see times where you have something like if you look at iron, iron has two different oxidation states, two different charges.
54:01
So a three plus and a two plus. And we have different nomenclature for certain compounds. For instance, iron. Where we call it ferrous or ferric. And those us and ick endings, those refer to the charges. If you have an ick ending, you would have a three plus charge. If you have an us ending,
54:21
you would have a two plus charge. The us always refers to the lower charge. The ick always refers to the higher charge. And so keep that in mind when you're memorizing those weird named ones, like iron and lead is another one, stannous and stannic for tin. So there's these groupings of ones
54:41
that have two different names. One comes from the original Latin root. The other one is the name that we know it by. And these are pretty easy to pick out of the periodic table because they're the ones where the element symbol doesn't really match up with what we know. We know that iron is Fe. We know that tin is Sn. And so those are pretty easy to pick out of the periodic table. And I have those highlighted on the study guides as well.
55:03
So make sure you go in, start working on memorizing those and start working on making sure that you can form those ionic compounds using the ions that you have memorized. Because again, you'll be tested on this all through general chem. And it's better to just do it now and get all the points starting now
55:20
rather than waiting till the end to do it. Next class, we'll get into how to name acids and how to name covalent compounds, which are significantly easier than this just because there's a lot less memorization to it. If this didn't make a huge amount of sense, make sure you go and look at the study guide online where it's all written out
55:40
with the O-U-S-A-A-T-E and I-T-E endings to help.
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