Yeah good afternoon. Your first exam is now nine days away. I know some people have been looking at the practice exam because some people coming to my office hours with questions. You haven't looked at the brightness exam yet would be a good time. To give you an idea of what you can expect. Next Thursday at your first exam. Everybody know what room you're supposed to go through for your. Some people read my emails and someday. I'll remind everybody later this knock you. Down A is to finish up what we're going to do a chapter five. We've been spending a lot of time recently talking about thermochemistry. Thermochemistry is the idol of chapter five. Thermochemistry is the study of the energy changes that accompany chemical reaction. We've been talking about delta H that will change how you can measure that. Well when you talk about I didn't measure that we're talking about a calculated using Hess's law given other information But one question that may have been in the back of everybody's mind when we were talking about this stuff before is we're gonna do all these numbers that we're winning games with last time. Answer is calorimetry experiments. The title of Section 5.2 is simply calorimetry. Before the semester is over. You'll have a laboratory experiment coming up titled simply revenue. So you will get some firsthand experience with this. Some of what I say today is hopefully going to serve as useful background information for that lab experiment that's coming Couple of months. For now we'll just say this gallery Madrid is the measurement of the temperature changes. That result from the energy changes that accompany chemical reactions. We've seen this problem before. The things we really want to know about we sometimes have trouble measuring directly. For example if we want to know about the mole amounts of everything involved in chemical reactions. We typically have to measure something else like a gram quantity of a pure substance or a volume of a solution and then convert that into moles Same principle here what we'd like to know about are the energy changes that accompany chemical reactions. We can't measure energy changes directly but we can do is measure temperature changes. And then through the use of various conversion factors that I'll be talking about today. We can convert that into energy information. I'm going to show you a couple of schematic diagrams and a couple of moments. Because calorimetry is described as either constant volume calorimetry or constant pressure calorimetry depending on what kind of apparatus you're using to make these measurements don't worry about the fact that a constant volume calorimeter is If a bomb calorimeter hopefully it won't be exploding during the course of the reaction. But in any case we're not going to turn you guys lose on a bomb calorimeter. We're going to turn you loose on the el cheapo piece of apparatus that still does the job reasonably well. And that is a coffee cup calorimeter. And I'll be showing you pictures of these things as soon as people are done with this slide. Anyway like war time with this one. All right let me just show you these pictures. Then it'll start looking at how we can actually obtain this information Here's a schematic diagram of a bomb calorimeter. The bomb is simply the vessel down here in which the reaction actually takes place. And just for argument's sake let's say it's an exothermic reaction which means it's going to be giving off me. Well and you can see is that it's been immersed in a water vat but a thermometer in there. So we can measure the temperature of the water bath. And if this is an exothermic reaction giving off heat to the water bath. That means the temperature of the water is going to be going up. But the point is we can record what the temperature difference is. Before the experiment at the end of the experiment. It will show you how I can draw some conclusions based on that Typical Bomb Calorimetry apparatus probably about somewhere between let's say ten thousand and fifteen thousand dollars. We're not turning. You guys loosen that. We're turning. The $10 address at $9.50 is the thermometer. Don't rig thermo. Cup of coffee cups to provide insulation. Turns out that it works reasonably well. As hopefully you will see when you go to the laboratory Nunez. But the point is no matter what kind of calorimetry experiment you're doing. Calorimetry experiments are based on something that you've probably heard of him before And that's the law of conservation of energy barrier this semester. And we talk about the law of conservation of matter. But who can tell me what the law of conservation of energy says yes. Just like matter cannot be raiders ride energy cannot be created or destroyed. However there are two things that we can't. Typical calorimetry experiment involving a chemical reaction. We do love. The law of conservation of energy. Energy is never created or destroyed. But it can be changed from one form to another They can be transferred from one place to another. Again going back to our exothermic reaction example. The reason the reaction is exothermic is because there are changes in chemical energy that take place during the reaction. And those changes in chemical energy manifest themselves as he that's given off to the surroundings. So we're changing chemical energy into heat that's changing from one form to another. And then typically that heat is radiated from the inside of the mom to the water bath it's outside. So that's what we mean by transfer from one place to another. Calorimetry experiments. The law of conservation of energy can be written in the form of a very simple equation. We said last time the hue is a symbol commonly used to represent heat. Conservation of energy for a calorimetry experiment. We summed up this way. Q lost IQ walls and negative q game. Specifically the amount of heat lost by one object is equal to the amount of heat gained by another object. And the only reason for the negative sign here is losing heat is an exothermic process which has a value associated with it But 80 is an endothermic process which has a positive value associated with the negative sign is there just to make the signs come out the same on both sides of the equal sign Everybody okay with that as he said a few moments ago we can't measure energy changes directly but we can measure temperature changes. Well that means we need some sort of conversion factor to get us back and forth between the temperature changes. We can measure directly And the energy changes which is what we really want it up. We've seen such conversion factors before. We is molecular weights to convert from gram quantities that we can measure to mole quantities that we want to know or we could use molarity in volume. We can measure for the same purpose. They get moles for things that are taking place in solution. There are two very common conversion factors that are useful in cavalrymen rig. The first is called the heat capacity. And the heat capacity of an object is simply the amount of heat we need to raise the temperature of that object by one degree Celsius Heat capacity simply has units of energy divided by temperature any energy units you want in the numerator like calories reviews any temperature units. You wanted the denominator typically Kelvins or degrees Celsius. The other is called specific heat. And specific heat can essentially be thought of as the heat capacity per gram of a substance. The specific heat is the amount of heat needed to raise the temperature of one gram of a substance by one degree Celsius. And the difference is in the units you will notice that there are no mass units for heat capacity. But As for specific he have grams in the denominator along with some sort of energy units in the numerator and also some sort of temperature units in the denominator. One of these two is an extensive property and the other is an intensive property. Can tell me which is which is specific heat is in fact an intensive property. That means heat capacity is the extensive property. That is the easy way to remember that Who knows what the specific heat of water is. Back there. Units plays. Okay and you're going to go for 0.18 it's joules per gram per degree Celsius. The other unit for measuring energy that we talked about before is calories. And I for one thing it's easier to remember one that is remember 4.18 whatever works for you. This isn't water is one calorie per gram per degree Celsius. But the reason you know that that's an intensive properties that I didn't have to tell you how many grams of water That was the specific heat. If I'd asked you what's the heat capacity of water Asia said Well that depends how much water do we have what would have a greater heat capacity teacup full of water bath water yes no. But thank you for playing our game. Let's think about it this way. What would it take more heat to raise the temperature of by one degree a teacup full of water or a bathtub full of water. Hopefully it's obvious that the answer is So a bathtub full of water would have a larger heat capacity of water. But if you scoop out one gram of water from the teacup or one gram of water from the bat that it's still going to take one calorie to raise temperature of that one gram of water by one degree Celsius. Concept makes sense. Ok we'll give people another moment or two with this slide and we'll start looking at the kind of problems you can solve by doing calorimetry experiments that for those of you following along in the lecture notes the first such problem I'm going to show you appears on page 15. In the Everybody have what they need from this line. Ok.. Now as I show you my slides you will see my crude of artwork. There Realize that when I show you what I'm about to show you it's really supposed to look something more like this to styrofoam cups nested inside each other water the veneer all that. Here's my proof version of the same thing. Now read this problem. A 70 gram piece of metal was heated to 77 degrees Celsius and placed in 100 grams of water at 22 degrees Celsius in a coffee cup calorimeter. Metal yeah the water came to the same temperature at 27 Celsius. Calculate the heat capacity and the specific heat of the meth. In other words if you were doing this in the laboratory saying here's your calorimeter over here. Thermometer says the water is at 22 degrees Celsius. Meantime over here you've got a water bath at 77 degrees Celsius and a test tube in there with an oddly shaped piece of metal in there. And then you dumped the hot piece of metal into the Cold War. And no surprise perhaps the temperature goes up. Okay now how do we go about solving this problem well I'm gonna take you right now The best place to start for solving any calorimetry problem is with the law of conservation of energy. Specifically written in the form of Q lost equals negative q game. Maybe the hardest part is interpreting what that means in the context of the particular experiment that you are looking at but I'm hoping for this experiment it straightforward. What's losing heat and what's gaining eat during this experiment. What's losing the mouth you heated the metal up to a high temperature you dump it into relatively cool water. The metal gives off some n0. So what's gaining me Water when you dump a hot piece of metal into cool water the metal gives off heat the water absorb c. So in this example the middle is losing heat. The water is gaining heat. Again the only reason well you'll see the reason for the negative sign and a few months. Okay so that's a good starting point for this. Now another thing we're going to be concerned about is not absolute values of temperatures but temperature changes. What's the temperature change of the water in this experiment. Yes. Temperature is a state function. Find temperature change. All you do is final temperature minus initial temperature. The water started out at 22.8 degrees and wound up at 27 degrees. So 27 minus 22. Change in temperature of the water is 5 degrees Celsius. How many sig figs Arthur and this time we'll see later why that's important. Alright so from the information that's on the screen plus what we said a moment ago about the specific heat of water. How can we figure out what that is how can we figure out how much heat was absorbed by the water What's the specific heat of water one calorie per gram per degrees celsius right okay so we know that we know to other things. You know the change in temperature of the water. We also know the mass of the water. We had a 100 grams of Turns out that if you multiply specific heat times mass times change in temperature you get Q. And you can see that because the units cancel out Specific heat as units of calories per gram per degrees Celsius. You can multiply by grams grams cancels out and you multiply by degrees celsius degrees Celsius cancels out. And the answer comes out galleries. And since this is an amount of heat it should come out in some sort of energy units like cameras or joules. So we multiply this out. The answer turns out to be 500 calories but I'm writing it this way 5 times ten to the two to emphasize the fact that we really only have two sig figs in that number because we only have two sig figs and the temperature change. Everybody with me so far Questions about anything that's on the screen. While people are still writing let me ask you this. If q water is 500 calories. What's Q mental negative 500 gallons. Because Q metal is just the negative of q one. Okay hold that thought while people finish with this slide will show you how we finish off the problem. Remember all we're trying to find here is the heat capacity and the specific heat of the metal. We need more time here. Okay so if the water gained 500 Camry is the mental must've lost 500 galleries hence the negative side for the 500 calories. But the data back up there. What's the temperature change of the in this experiment Positive or negative. Yup the metal started out at 77 degrees Celsius. But eventually the metal and the water both wind up at the same temperature 27 degrees Celsius. The metal decreased in temperature by 50 degrees. In other words delta T is still final temperature minus initial temperature. In this case it's the final temperature is lower than the initial temperature when you track is going to come out to be a negative number negative 50 degrees Celsius It turns out that the fact that this is negative this is negative is important. Because the next thing we're going to do is simply divide those two and the negative signs are going to cancel out. We're gonna get a positive value for the heat capacity of the metal. And that's important because heat capacities and specific heats are always positive numbers. So if you ever get a negative number for a heat capacity or specific Eat. Well I can't think of too many substances where when you pump heat in the temperature goes down and that would be what a negative heat capacity or specific heat would mean. Anyway defined the heat capacity They simply divide for the middle negative 500 memories by delta T for the middle negative 50 degree Celsius. We still only have two sig figs and the answer to the answer comes out ten calories per degrees Celsius. I'm writing it this way to emphasize the two sig figs but the point is the answer is ten calories per degree Celsius. From there how do we get the specific heat of the metal yes. Google specific heat is essentially heat capacity per gram. So we divide by the mass of the metal. And from the previous slide the mass the metal turned out to be 70 grams. So if we divide this out and take the two sig figs were allowed. We find that the specific heat of our piece of metal is 0.1. four calories per gram per degrees celsius. What as a larger specific heat this piece of metal or water. What's the specific heat of water one calorie per gram per degree Celsius. This is obviously less than that metals in general tend to have relatively small specific heats compared to one. And this is a phenomenon that I suspect you've had some experience with few months from now it's going to be wintertime. People are going to want to warm themselves up with hot cups of coffee hot balls assume things like that Suppose you're enjoying a hot cup of coffee or a bowl of soup. You've got a teaspoon and the coffee cup or a soup spoon and symbol. And then your phone rings and you go talk to soft money for a few minutes. Meantime you left that metal spoon in your hot coffee or your hot soup whatever it is. You come back in a few minutes and you grab that metal spoon and what do you notice it's a lot harder than it was a small specific key like this is that it doesn't take a whole lot of energy to raise the temperature of metal significantly. So you put a piece of metal something like water that's at a higher temperature Pretty dramatic effect once you check out the middle again. Concepts make sense arithmetic make sense. Okay that Calorimetry problem is probably very similar to something you're going to be doing when you do the calorimeter your laboratory experiment and then a few weeks. So make note of that and come back to that but it's time to consider that next. But let's look at the next problem that appears in the lecture notes. And again this is by crude picture of a coffee cup. Calorimeter Let me just read the problem appears on page 51. In the lecture notes. A sample of silver nitrate way 5-0 Rams was dissolved and 91.5 grams of water in a coffee cup calorimeter. The temperature of the water was 23.4 degrees Celsius originally. But the addition of silver nitrate produced a rise in temperature of the solution reaching a minimum temperature of 20.7 degrees Celsius. Calculate the molar solution of silver nitrate that is calculate delta H for this reaction. Here Express your answer in kilocalories per mole of silver nitrate. Assume that the heat capacity of the calorimeter is 0 and the specific heat of the silver nitrate solution is one calorie per gram per degrees celsius. Alright where do we start solving account really regrow yes. Law of conservation of energy. He lost equals negative two again. What's gaming heat here. Now this may not be immediately obvious. So I'll give you a hint. Is the temperature going up or going down going down. Why don't the reason why is because we're dissolving the silver nitrate in the water. If the temperature is going down if you were to stick your hand in there would feel cooler. Does that suggest that this reaction is exothermic or endothermic yes it would be endotherm. Let's go back to something. We said last time. Bunsen burner burning in the lab. You gotta stick your hand in it. First that's why too hot or too cold too hot. If it feels high that's because the reaction is giving off. That's an exothermic Grant. Here the temperature is going down. Stick your hand in there with your cool. Therefore is because this process is absorbing. What's gain here is the reaction is taking place because it's an endothermic reaction. So what's losing me yes the water. Water is part of it Compare this to the previous example. In the previous example we dumped a hot piece of metal and cool water for making a mixture we did. In the previous experiment we're making a homogeneous mixture or a head or a heterogeneous because we wanted to we could reach in there and pull out the piece of metal. When we dissolve silver nitrate and water homogeneous mixture or a heterogeneous mixture. Homogeneous mixture. By the time this process is you don't just have pure water anymore. You have a solution. A moment you'll see why that's important to bear in mind Okay so here's how we define q loss equals negative q gained for this reaction. Now what can we do to solve this brown Yes. Okay so how do we solve for HIE Ok keywords I was looking for there were changing temperature sooner or later have to figure out our change in temperature its final temperature minus initial temperature. And in this case temperature 20.7 degrees Celsius initial temperature 23.4 degrees Celsius. So practice to it's going to be a negative number because the temperature is going down negative 2.7 degrees Celsius we then we'll add to say. Ok. Now while you're jogging that information now Let me remind you that the problem stipulates that you can ignore the heat capacity of the calorimeter itself. Part of the reason that Styrofoam coffee cups do a pretty styrofoam has a very small heat capacity. And you can assume that the specific heat of the solution is the same as the specific heat of water which is one calorie per gram per degrees celsius. So we know the temperature change. We know that the specific heat what's the mass of this solution yeah there we go. The two things we mix together to make this solution or 91.5 grams of water at 8.5 grams of silver nitrate. So the mass of the solution is the sum of those two. So to solve this problem we are going to use specific heat times mass times change in temperature. But the important thing to realize that the mass of the solution is the sum of the masses of the water and the silver nitrate. And it turns out that that's a 100 grams So now you can multiply all these things together and it goes out to be negative 270 calories. Again I'll make two sig figs here. So negative 2.7 times ten to the two. Now at this point we are almost the problem said it wanted the answer in kilocalories per mole of silver nitrate. Before we get to there this is q for the solution. What's Q for the reaction Q for the solution is negative 270 calories. Q for the reaction is positive 270 galleries. You lost equals negative. Okay so how do we convert calories into kilo calories per mole I gotta do two things yes. Divide by a thousand calories kilocalories. And then divide by the number of moles of silver nitrate. Okay yeah 8.50 grams of silver nitrate that we use to make our solution. Silver nitrates formula is 169.87 grams per mole. You divide that that would be 0.0500 moles. And then the finished they saw it your positive 270 cameras Divide by 0.0500 moles of silver nitrate and divide by 1000 to convert galleries into kilocalories. And if you do all that the two sig figs you're allowed delta H the heat of solution of silver nitrate turns out to be positive 5.4 kilocalories per mole of silver nitrate. You told me before this was an endothermic reaction which is correct. So the sign of delta H should be a positive number. And in fact it is Are there any questions about any aspect of this brow while people are finishing with this. By now I'm sure that thought has crossed a few of your minds. Why does anybody care about this well let me just show you an illustration from your textbook Whenever you are going to be a good thing to do at this point because some people might begin to rebuy macaroni and cheese and a nutrition. Nutritional labels. Oh I see the rest of you just eat whatever comes out of a vending machine. I brought along with me today to rather ancient food packages that I have held onto for more years than human alive. And there are reasons. Now how well are you going to be able to see the reasons I don't know on this screen Before that many years ago I attended a chemistry conference in Toronto Ontario data. They had us in a nice hotel. They had a nice breakfast bar. We could go to every morning and get anything you wanted with breakfast bar including little packages material like this. Let me see if I can get close enough to this. You can see what's going on. My guesses timing it close enough. It'll be too pixelated for you to see much. Okay we'll try first of all canada smiling. So when I look at the information here another we see the nutrient contribution per 100 grams of cereal. See the value t par song grabbed this at a out. So I can get into languages. But there is also a civilized metric speaking country find out about calories here and find out how much energy I'm getting from eating this theory in both Calories with the capital C and kilojoules. So there's that and the other is this fancy package of imported chocolate almond cookies. And again the reason they've held onto this for as long as I have. Here is on this matter And we've seen this where among other things I can find out how much sodium and potassium are in these things not only in milligrams but also a milli moles. I had never seen bowls on the side of food baggage. And I haven't since those are not the reasons why most people read food labels those B or a food label to see if what they're about biggie is consistent with what diet they happen to be on that week. And it turns out that a lot of the information on food labels comes from calorimetry experiments. Specifically bomb calorimetry experiments The point is when the Food and Drug Administration gets hold of this and they spend lots of taxpayer dollars to get the expensive instruments. Measure a few more sig figs. Then they can tell you about how many calories are in your food based on Bomb Calorimetry literally they take samples of food and burn them inside them up and measure how much heat is given off. Because when you burn a sample of food inside the bomb you are basically doing do it. The same thing that your body does do it. Except of course your body. Does it much more slow here's a problem that appears on page 52 of the lecture notes They teaspoon full of sugar about 5 grams. Let's place in a bomb calorimeter which had a heat capacity of 1-zero kilojoule per degrees Celsius. The calorimeter was immersed in a water bath containing 1-zero and leader of one. The sugar was combusted completely in the bomb clothing the temperature of the water to rise from its initial value of 24.96 degrees Celsius to a maximum value of 40.96 degrees Celsius calculate the amount of energy released by this reaction and compare your result and the advertisers plane that sugar contains Lee 16 calories produced. But. Where do we start solving any calorimetry Robin yes. Say it changing. I mean yes you whale eventually but that's not restart. Yes law of conservation of mass. Everybody say it again law of conservation of gans media back there law of conservation of mass. For solving any calorimetry problem you start with Lost equals negative game. Now let me just remind you that despite my lousy aren't hurt here's the picture that shows you what it's really supposed to look like. We're burning the sugar down here. Heat being given off to the rest of it. So in the burning of sugar in the bomb calorimeter experiment what's losing he once gave me what's losing the sugar or essentially the reaction the sugar is undergoing. Okay exothermic reaction you're burning sugar. Gaining He water. Certainly what else when the reaction takes place about deer lots of heat given off the heat flows through the bomb to get to the water. And the point is the capacity of the non-zero. So the bomb itself is also going to be absorbing some he yes the water absorbs some heat but so does the bomb. We have to account for both of those things. Now of course we do find the change in temperature. So in this case water started out at 24.96 degrees Celsius wound up at 40.96 degrees Celsius. Now we're using the expensive thermometers that can measure down to the nearest 100th of a degree. So I'm going to actually get four sig figs ON THE temperature change. By the way that's the temperature change of the water. That's also the temperature change of the pot. Because the bomb is in contact with the water and therefore is assumed to be the same temperature Okay now what have we find either q water or Q by B what information do we have okay now the heat capacity of mob 1-zero kilojoule per degrees Celsius. And we also know the change in temperature them out. So we should just be able to multiply those two together and find Cuba. About Q_1 what are going to have to do for that what do we know that the what Yes we know the specific heat of water is one calorie per gram per degree. Change in temperature. We know the mass of the war. We kinda do because we know we have one liter of it. How many milliliters either an elite ten hundred ten hundred milliliters of water. What's the density of water one what units grams familiarly so 1000 millilitres of water So you have 1000 grams and so we actually do know the mass the setup for the heat capacity 1-zero kilo joules per degree Celsius multiplied by the change in temperature which is 16 degrees Celsius. Now the question wants to know about how many nutritional calories there are in a teaspoonful of sugar That's why I'm throwing in this conversion factor. For 0.184 joules is the same thing as one calorie is 4.184 kilo joules is the same thing as one kilocalorie. And kilocalories are the same thing as nutritional cowards. So Bob comes out to be 3.82 kilocalories here for the water. The specific heat one calorie per gram per degree Celsius change in temperature is the same 60 Boyd zeros 0 degrees Celsius. And we have a 1000 grams of water because we have 1000 milliliters of water. And that's one For the density at one comes out to be 16 thousand if the little c calories or we divide that by a thousand to convert into kilocalories 16 kilocalories. So now that we know both of these we can figure out Q for the reaction. Because Q for the reaction is just the sum of these two made negative. So part of the question was compare what you get with the manufacturer's claim that sugar contains only 16 calories per teaspoon The answer is maybe not I guess maybe depends on whether it was a level teaspoon or a heaping teaspoon. Maybe they just ignore q for the bomb because this comes out to be 16. But the point is if you add these two numbers together and make it negative it comes out negative 19.8 kilocalories which is the same thing as negative 19.8 nutritional calories. Now the point is this is one example of how you can take a food sugar and burning in a bomb and get information about how many calories you can get from that particular thing People have done a lot of experiments like this and compile a lot of information about different kinds of food stuffs. So why are copying this down let me just ask you this. There are three main kinds of things that people consume for nutritional value proteins carbohydrates and fats. Which of those three is sugar a carbohydrate. The one thing we didn't do with the data that we had party Spoonful of Sugar wait five grams. If we take our mentees and in calories and divide by five grams. It comes out to be pretty close to 4 is people have studied carbohydrates across the board. And just about all carbohydrates if you for nutritional calories per gram. Kinda let you know where the word carbohydrate comes from. Earlier we said that the formula for sugar sucrose or table sugar C12 H22 O11. That's how most people would write. But you could conceivably write the same formula this way. C 12 H2O parentheses 11. In other words you could write it as though it was a hydrate of carbon. Now a sugar molecule is not 12 carbon atoms with 11 water molecules start doing. But you can write the formula as though it was. And that's where the term carbo high-grade comes from. Proteins also give you for nutritional calories per gram. Baby not too surprisingly. Fats are the ones that do a little bit more damage. They give you nine nutritional calories personally. But the point is Where the information on food labels comes from like for example when I want to know how many nutritional galleries and getting per 100 grams of my fancy cookies here. Well if I just look at the gram quantities of proteins carbohydrates and fats that are listed on the serving size. And I can just multiply proteins by four carbohydrates for fats by nine. Out of up I should get the tow. And then it depends on what diner on that week if you're low carb then you don't want to have very many carbs in there. If you're low fat you don't want to have any types and they're probably pretty much no matter what you do. You don't want to eat those cookies but Anyway concepts make sense. Ok. So for those of you who are interested in nutrition for whatever reason. Next time you look at a food label calorimetry experiments that's where it all comes from. For the rest of today. And we don't have that much time left today. You're going to completely switch gears. Enter calculators out whatever way. Before I go on and talk about Chapter six. Well I'll talk a little bit more about the periodic table. So let me just ask you this question. Who was the main treatment delay gap is basically the guy generally given credit for having developed created the periodic table. Linearlayout once a professor of chemistry and a Russian university back about the middle of the 19th century. And he decided that he wanted to write his own text For his students to use during his classes. And as part of that textbook what do you want to do let's compile information about all of the elements that were known at the time and have it all in there. So students could look it up if they had to. So what he did was to take a whole bunch of different pieces of paper. Put each element on a separate piece of paper write down information about its properties. And then he laid out those pieces of paper in order by increasing atomic weights. Bear in mind that this is the 160s. And we didn't know that things like protons neutrons electrons at that time So atomic weights was the best we could work with. What personally I've noticed was that okay suppose we have this element right here whose properties are summarized by this read x a little bit later on down the line when delay and saw that there was another element with properties also similar to the green x properties from the previous owner. And then a little bit later on. And here's another element with those same green edge properties that we'd seen before. Meantime if this red hues summarizes a different set of properties again a little bit further down the line. We encounter another element with property Where to those of the read queue element babies but in other words what Mendeley noticed and formulated into what came to be known as the periodic law. Is that the properties of the elements repeat themselves every so often that is periodically. When the elements are arranged like this in order of increasing atomic weights. So Mendeleev's day instead of having everybody memorize everything. But we do it this way or combat the other slide bistable. The middle a sense laying things out in a straight line when we lay things out in a rectangular array something like this. The idea being that elements with similar properties would be in the same columns. All the green x's in this column over here on the red cuz at this valuable renew less memorizing for my students. So I felt so sorry for those of you who were made to memorize the periodic table. Given Mendeleev didn't do that and looking for ways around. But there was another interesting aspect of laying things out this way Remember this is the 160s. Haven't necessarily discovered all the elements at that time. For example to elements that were known at the time were silicon and tin. But when Mendeleev laid out as pieces of paper this way he saw that there was a hole between silicon and tin. And so he basically thought hm. Maybe there's something that's supposed to be in that hole and we just haven't discovered it yet. Mendeleev call that undiscovered element ICA silicon and was able to make some predictions about the properties of IQ a silicon based on the properties of silicon 110 which were known at the time. And then some years later when the element that we now call it germanium was discovered it turned out to have properties very similar to those that Mendeleev predicted using the hole it is periodic thing. So the point of a good scientific law is not simply to summarize what is already known. But to hopefully allow you to make predictions of what might happen in the future. And Mendeleev's periodic lot turned out to be a very good example of why did writing let me see. Let me just find the handy periodic table somewhere Most textbooks have one on the inside front cover this textbook as a notable et cetera. But it's years. Okay here we go. But anyway like more time buddy. Okay. Let me just show you this periodic tables in your book. A 95 Let me see if I can zoom in close enough to this one spot showing if not no big deal you can always look it up later yourself. Okay as you know the periodic table these days it's laid out in order of increasing atomic number. Mendeleev did it by atomic weight. For the most part that doesn't make too much of a difference. Because in general as the atomic numbers increase the atomic weights increase also. But there are exceptions to that state. And I'm looking specifically at tellurium and iodine here is atomic 52 iodine has atomic number 53. So iodine has a higher atomic number than Silurian does. But I think it's atomic weight is 126.9. Tellurium is 127.6. So even though it's alluring as a smaller atomic number it has a larger atomic weight. And if you look over the rest of the periodic table you'll find a few other examples that sort of phenomena. So while Mendeleev's method using atomic weights worked reasonably well for the time. About 50 years later when we figured out There were such things as protons neutrons and electrons. It didn't say somebody very long to redo the periodic table using atomic numbers. And they found out that things line up a little bit better. What do you use a topic numbers so the modern version of the Periodic Law looks a lot like Mendeleev's periodic law. The only difference is that instead of increasing atomic weights w0 is increasing atomic numbers now. Oil surprise anybody. But that's how those things came to be We're running it. One more slide show. And please do not knock yourself out trying to copy down everything that isn't on this slide. Because the purpose of this slide just to introduce some terminology Much of that terminology you'll actually find on the bottom of page 95 in your textbook or any of that periodic table that I just showed you. And let me just walk you through this real quick. And again depending on how much exposure you've had in the periodic table we bought this much of this may already be familiar with the horizontal rows or gamma ray just call rose. Somebody who'll play periods but in general hydrogen and helium are thought of as first row elements lithium beryllium etc. Over to the second row sodium magnesium etcetera over of Argon third row cancel The vertical columns are called groups. These days a lot of people number of the groups one through 18 left to right. There's this older system that uses Roman numerals and letters I actually think is more useful. So that's probably the one I'm going to use. The first column here is called roman numeral one. A next to that we have Roman numeral today. Then we start with a B 3B 4B 5B et cetera. And then about halfway through the periodic table. We start over again with one B to B and then back to three except now we're back to the aids a3 a4 a5 a et cetera all the way over here to date. There's a reason for the A's and the B's. The A's are known collectively as the main group elements. And for the most part most of the chemistry we're going to be talking about for the rest of this semester is going to center around the chemistry of the main group elements. You're going on to other chemistry courses beyond this one. You may talk in more detail about the chemistry of the B elements known as the transition metals. We've already seen some examples of how the transition metals are not quite as well behave as somebody other elements are. So we focusing mostly on the main group elements and not doing too much with the transition metals for the rest of the semester Some of the elements in a particular groups are known by a particular group names. For example group one a hydrogen lithium sodium potassium and so on are known collectively as the alkali metals. Now hydrogen is not a metal but everything else in there. And we'll talk later about what this alkali thing meetings. Likewise the bells and grew to a beryllium magnesium calcium and so on are called the alkaline earth metals. On the right side of the periodic table helium neon argon etcetera are known collectively as the noble gases. They used to be known as inert gases because it was believed for a long time that they would never do any chemical reactions. We have since found that that's not quite true. We can make some of them especially xenon and krypton actually do a few chemical reactions. So now they're called the noble gases because they are sort of like the nobility and the periodic table they roll them up and sold with those other Pullman. Illinois you know what I mean group 7A fluorine chlorine bromine iodine known as the halogens or salt formers. And there's some other terminology that comes up here. And a couple of other things let me point out real quick. For the most part as you go across the horizontal rows the atomic numbers go up pretty much uniformly until you get to here. And then it's 5567. All of a sudden 72. Same thing that eighty seven eighty eight eighty nine all of a sudden that pattern for. Where are those other elements disability they disappeared down near the bottom. Element number 57 his poem lanthanum. The elements that follow lanthanum are known as the length of L1 number 89 as the elements the fatherland recall the act and the reason we show these things down here. It's not because they're not important. They actually are for many reasons. But my shipping them down beer we wind up with the periodic table that can fit conveniently on an eight by 11 piece of paper. If we put these things where they belong which is right here that the periodic table would be about this line about this tall. And that doesn't work for an eight by 11 piece of paper. So seriously that's the main reason that's wrong. But hopefully you know where to find it I'll be talking about more in detail next time is the distinctions between the metals and nonmetals metalloids and use the periodic table to say more about that. I'll see you Thursday I see. Yeah that's the point. You want to come see me. That's what I'm going to be. You want to see me at some other time and it'd be a good idea to send me an email or your text. So that you're comfortable with. And we talked about so far. And I think this isn't why is it going to be centered in disability services and accommodations services well the question is not whether the question is whether they have you talked to that point is there. Then what they'll do is send me an email. And all I often say It's OK. So the point is as long as you got everything straightened out the DSS office is not going to be around. I didn't believe axis or that boy. Yeah some people are going to have to do different timing for that. Yes. Alright thank you work all that out of the DSS office. Has sent me an email give because people were that there was one before. So let me show you that with some alcohol. For one problem. You didn't have to account for the mass because the specific heat capacity per month about ten degrees Celsius that's one degree salesman exercise yeah okay the point is that's a that's a heat capacity has its own specific. For specific heat capacity. You're basically just yes yes as we said always as units of grams cancel out. Yeah. Yeah
chem103-080-20190924-140000.mp4
From Dana Chatellier September 24, 2019
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