Program 25 - "Laws of Chemistry and Atomic Theory"

 

Music I don't know where they are.I know they were in here someplace.I know I used it and I'm really sure I put them back in here.Woman: "What are you looking for?"I'm looking for my atoms.You know, my atoms.Woman: "Your atoms?"Yeah, I had a whole theory of them here.I really need them.Woman: "You're never going to find atoms in a drawer, you can't see them."I had them here before.What am I going to do?I have to have them.I need them for today.Woman: "Why don't you use Dalton's?"Dalton's?Woman: "Dalton's theory of atoms."Oh, yeah.MusicSilico: "We are back with Science 122, the Nature of Physical Science.We are the telecourse that shows you how to find things that can't be seen.This is Program 25, Lesson 4.3, the Laws of Chemistry and Atomic Theory."Before we're done with this program we will have learnedabout the laws of chemistry and how they led an opinionatedschoolmaster named John Dalton to formulate a new theoryof atoms based on these quantitative laws.

 

We will learn about the law of combining volumesand the ensuing controversy which was finally resolvedafter Dalton's death by Avagadro's law, with the elegance we havecome to expect from physical theories,and which allowed us to calculate the atomic weights of atoms.At the end of the program we'll turn our attention to chemicalsymbols and equations and introduce a discussionof the combination of the Newtonian world view with the atomic paradigm.Here are the objectives for today's lessons.These objectives are also in the Study Guide at the beginning of the lesson.Before you begin to study the lesson, take a few minutesto read the objectives and the study questions for this lesson.Look for key words and ideas as you read.Use the Study Guide and follow it as you watch the program.Be sure to read these objectivesin the Study Guide and refer to them as you study the lesson.Focussing on the learning objectives will help youto study and understand the important concepts.Compare the objectives with the study questions for the lessonto be sure that you have the concepts under control.

 

In this program we want to talk about the lawsof chemistry and atomic theory.Hi, you know the world would be very dull and lifeless if it wascomposed only of uncombined elements.In fact, most of the substances that we use and are awareof are combinations of elements in various types.It's these combinations of elements which create the richvariety of substances which comprise the universe and life, itself.We'll see in this program that combining the propertiesof elements require the assumption of discrete properties of matter.In other words, the atomic nature of matter.Lavoisier, remember, had set the stage for determining thelaws of chemistry by doing several different things.First of all, he discovered that general rules apply to chemicalreactions, and secondly, and probably more important isthat he discovered that the weights of chemicals are important.And, even more important, still, is that he showedus how to recognize elements.

 

Elements are those things which cannot be furtherbroken down into their constituents.He also showed us that mass was not lost or gained in chemical reactions.In other words, he showed us that things don't justdisappear and appear spontaneously.This was also important.This is why we call Lavoisier the father of chemistry.After Lavoisier's time, in fact, within a very short periodof time, other chemists worked to discover other quantitativelaws which are the laws of chemistry.And these laws, as we'll see as we progress throughthe program, led to the atomic theory.The atomic theory basically as we recognize it today in its modern form.The laws of chemistry are very basic to the science of chemistry.And they serve the same function in chemistrythat Newton's laws served in physics.That is, they give us a paradigm or a basisfor understanding chemical reactions.There are six of these laws.Three of them we'll talk about now, two we'll do laterafter we learn about atomic theory, and one of themwe won't cover in much detail at all.The six laws are: conservation of mass; the law of constantproportions; the law of multiple proportions;the law of combining volumes; Avagadro'slaw; and the law of mass action.

 

Now these laws are very simple to understand, but we still need alittle background on them to understand exactly what we mean by each of them.The first chemical law is simply the law of conservation of mass.This is Lavoisier's law.The total weight of the products equals the total weight of the reactants.This seems almost unnecessary to say in our modern terminology.But remember that in alchemical times it was knownor it was thought, anyway, that elements could spontaneouslyappear and change into other things.Another way to say this, of course, is that mass is neithercreated nor destroyed in chemical reactions.Mass is something which does not simply disappear and come back.You can say it this way:You'd have 1000 grams of lead and combine it with 77 gramsof oxygen, what you'll get is 1077 grams of lead oxide.One thousand plus 77 equals 1077.There's no in betweens.It happens every time.Every time you form this reaction, you get the same amountof products as you started out with, with the reactants.

 

The second law is the law of definite proportions.This law is a little more complicated, but not really very complicated.It was difficult to discover.And, in fact, there was a controversy surrounding this.The controversy had to do with two Frenchchemists named Proust and Berthollet.In fact, the two of them each announced that they haddiscovered contradictory laws around the same time, somewhere around 1800.Proust announced that elements combinedto form compounds in a fixed proportion by weight.On the other hand, Berthollet announced that elementscombined to form compounds in variable ratios.How could the two people both come up with suchcontradictionary laws using the same experiments?Well, what happened was that Berthollet heated copper and tin.This is two separate experiments, one time copper, one time tin,to form what seemed to him to be a continuous seriesof compounds of various compositions.And as a model he cited solutions, alloys and glasses as similarmodels, things that do combine in fixed proportions.What we referred to as physical changes in an earlier program.Proust was able to show that Berthollet wasanalyzing impure compounds.In fact, there were actually more than one compound involved.So, the law of definite proportions as stated by Proust and later on,proved by Dalton, himself, simply says that the relativeamounts of the given elements is always the same in a given compound.To go back to our example of lead, 1000 grams of lead plus 77grams of oxygen always gives 1077 grams of lead oxide.

 

Now here's where the law of definite proportions comes in.If you have an excess of either lead or oxygen, the remainderwill simply not combine and you will be leftoverwith that substance in its original form.So, if you put lead and oxygen together in a containerwith excess oxygen, after the reaction is over,you'll have lead oxide plus the extra oxygen.Or, if you have excess lead, you'll have lead oxide plus the extra lead.So, if you doubled the amount of lead to 2000 grams, you'll findthat exactly twice the amount of oxygen is used.So you'll get 2000 grams of lead plus 154 gramsof oxygen to form 2154 grams of lead oxide.The ratio is always the same.In other words, 93% of this compound is always lead and 7% is always oxygen.This particular lead is yellow lead, it's the lead oxide thatwas often used in the dye for paints before lead poisoningbecame such a serious problem, is only oneof the oxides of lead, as we'll see.But it always turns out that the composition of this is 93% lead and 7% oxygen.The law of multiple proportions is the more complicatedof the three, but it's still not really complicated.It just involves the concept of ratios and numbers.Let me state the law for you first, and then we'll come backand look at some examples and then I'll show you some numbers.

 

The law of multiple proportions says this:If 2 elements combine to form 2 or more differentcompounds, then a simple ratio exists between the 2 weightsof 1 element that can combine with a fixed weight of the other.If 2 elements combine to form 2 or more differentcompounds, then a simple ratio exists between the 2 weightsof 1 element that can combine with the fixed weight of the other.Let's give some background on this and I'll come bac and show you with numbers how this works.Remember the controversy between Proust and Berthollet,Proust was able to demonstrate that Berthollet was seeingvarious mixtures of 2 separate compounds of copper and 2 of tin.By heating them in closed containers with insufficient airor in open containers for insufficient time, the reactiondidn't go to completion, and so there were 2 compounds formed.The law, itself, the law of multiple proportions,was established by Dalton around the same time that Proustand Berthollet were having their controversy.So, here's the way it works.Two elements may combine to form more than 1compound in more than 1 different way.Each different compound has a unique fixed percentage of the combining elements.And if they do, the ratio of the weights of the 2 elementswhich combine with the same element is always an integer.

 

Let's go to the ELMO and I'll show you an example of what I mean.OK.So, we had before 1000 grams of lead combines with 77 gramsof oxygen to form 1077 grams of lead oxide.So this is a completion reaction.But it also turns out that 1000 grams of lead will combinewith 154 grams of oxygen to form another compound of lead, 1154 grams..So here's, this is a brown lead oxide, and this is a yellow lead oxide.So the law of multiple proportions is simply noting that the ratioof these 2 numbers is a simple ratio.In other words, the ratio of 154 to 77 is equal to 2.OK, so, here you have, if 2 elements combine to form 2more different compounds, then a simple ratio exists between the2 weights of 1 element that can combine with a fixed weight of the other.So, there are many different examples here.For example, the reaction of oxygen carbon, so you can have16 grams of carbon reacting with, I'm sorry, 16 grams of oxygenreacting with 12 grams of carbon to form carbon monoxide.A total of 16 plus 12 or 28 grams of carbon monoxide.You can also combine 32 grams of oxygen with 12 grams of carbon to form another compound.This compound is called carbon dioxide.The total weight here is 44 grams, but that's not what concerns us,what concerns us is this number.The ratio of the 2 numbers is 32 over 16, which is 2.So, once again, there's exactly twice as much oxygen combiningwith the same amount of carbon just as up here, there was twiceas much lead combining with the same amount of oxygen.I said that backwards.Twice as much oxygen combining with the same amount of lead.

 

The compounds nitrogen and oxygen make a very goodexample because there are five different combinations.I think if we go into the table we can see how this works.Here are various compounds of nitrogen and oxygen.There are 5 of them altogether.The combinations here, it's not so much that we careabout the exact amounts, but look at the different weights.Here the simplest of these compounds uses 16 gramsof oxygen and 14 grams of nitrogen.The next uses 32 grams of oxygen and 14 grams of nitrogen.The ratio here between the oxygen use for the same amount of nitrogen is in the ratio 2 to 1.Another compound of nitrogen uses 28 grams of nitrogen and 16 grams of oxygen.Here the ratio of oxygen is 1 to 1, but the ratio of nitrogen is 2 to 1.In other words, twice as much nitrogen is used here as here.And, in fact, if you look at each of the numbers in the table,you'll see that all of the weights of the various, 2 variousconstituents, nitrogen and oxygen, are always in some multiple of either 14 or 16.OK, so 14, 14, 28, 28, 28, all multiples of 14.For the oxygen it's 16, 32, 16, 32, oh, here's an 80.But 80 is 5 times 16.So all of these compounds use oxygen and nitrogenin some ratio of the numbers 14 and 16.This is what we mean by multiple proportions.

 

John Dalton is another one of those characters in sciencewhose personality plays a great role in his theories and in his ideas.Dalton was not known for being a genius.In fact, he was known for being a little slow, which is notnecessarily a criticism, because even though he might have beena little slow, he was very persevering.And it was really the perseverance that led him to the atomic theory.Dalton was a Quaker schoolmaster who was not formally educated at all.In fact, he started teaching school having taught himself howto read and write; started teaching at the age of 12 in Manchester in England.As he grew up, he, of course, learned more and more thingsand regularly attended the Manchester Philosophicaland Literary Society meetings.This was a scientific society much like the Royal Societyof London, only a much smaller version.Manchester, at that time, was not a very big city, and still isn't, in fact.So, the meetings were not nearly as exciting nor well attendedas those in London, but still, people from the countrysidecame around to deliver their scientific theories.Dalton, at these meetings, heard many of the scientistsdiscussing these controversial laws of chemistry.The ones we just talked about.They were controversial, not so much in that they were notaccepted, but they were controversial because there wasno explanation for the laws; there was no theory asto why these laws should work.What Dalton really did was to hear these concrete evidencesfrom many experiences, which involved thecombining proportions of substances.He saw that the laws of chemistry could be best explainedby assuming the existence of discrete individual particleswhich he called atoms, and the atoms had certain properties.He published this in a book called, "The New System of ChemicalPhilosophy" in 1808, in which he explained the laws of chemistrywith this new revised atomic theory.

 

 

 

It's also interesting that Dalton's accounts of how he cameabout and how he discovered the atomic theory differfrom time to time when he told it.And, in fact, what he told his own contemporaries, what he wrotein the book, and what he told other people, was all different.So we don't really know exactly what steps he took to comeup with it, but he did come up with the atomic theoryand we can go review what he said about the atomic theory now.Now we can look at Dalton's atomic theory and see exactly what he said.It turns out that the theory, itself, is not really that complicated.In fact, it's almost obvious.First, I'll tell you the general characteristics of the theory,and then we'll come back and look at some details.Elements are collections of only one kind of atom.This is the first rule of the theory.Compounds are made of molecules which are combinationsof atoms, and that atoms of a given element are all the same,and elements of different elements are different from each other.And what distinguishes the atoms of one element from atomsof another element is that the weights are different.So that's the basics.

 

Now, let's take a look at the details.The first of these is that all matter is made of atoms.This is basically a revival of the ideas of Democritus,the concept that the atoms are indivisible and thatatoms are the building blocks of substances.Now this, for the first time, has unified the concept of atom and element.Remember, before, that I had mentioned that ideas hadbeen separate, up until this time.The next thing is that all atoms of the same element have the same weight.That is, they have the same weight, the same size, and the same behavior.In fact, all atoms of the same element are exactly identical to each other.If different atoms of the same element had different weight,for example, how could you explain the law of constant proportions.We will see that this law turns out not to be quite true,because there are isotopes involved, but we'll, for now,take this to be at least a good approximation.

 

The next thing is that during chemical reactions, atoms are rearranged.They're never created or destroyed, so all of the atomsthat are present before the reaction are also present after the reaction.And, of course, this means that the weight of all the reactantsmust equal the weight of all the products since nothingis lost or gained in the reaction.This, of course, goes along with the law of conservation of mass.The next thing is that when elements combine to formcompounds, each group of atoms is identical.This, of course, gives us the law of definite proportions.Because all of the molecules of a compound are identicalto all the other molecules of a compound, and, of course,if that's the case, then the ratio of atoms in a given compound is constant.So, each compound has a fixed chemical formula and eachchemical, within that formula, has the sameratio of one kind of atom to another.

 

The next thing is then, of course, is that differentgroupings of the same atoms are possible.In other words, the same atoms can combinewith each other in more than one way.This gives us the law of multiple proportions.So, there is one last thing, by the way.Here in the law of multiple proportions you can see thatthe elements combine with each other in many different ways.Go back to the example of nitrogen and oxygen,there are 5 ways in which they can combine.And I think you can see here that using the atomic explanation,explains these 5 different substances of, known as thenitrous oxides and look at the ratios.Here the simplest combination exists in the ratio 14 to 16.This is because each oxygen atom weighs 16/14 as much as these nitrogen atoms.In other words, the weights are in the proportion 16 to 14.In the compound NO2, you have 2 atoms of oxygen,

so the total weight is 32 grams.That's 16 times 2, 1 nitrogen atom, the total weight is 14.Each of the successive compounds, you can see that the ratioof the oxygen atom weight to the individual oxygen atom weight,depends upon the number of oxygen atoms in the compound,and the same goes for the nitrogen atoms.So, in the substance that we know as N2O5, the total weightof oxygen per molecule is 80, which is 16 times 5.I should also point out that these particular nitrogen compoundsare fairly difficult to separate, and, in fact, when nitrogenand oxygen react, which they don't always do easily.But they do, for example, inside internal combustion engines,inside the gasoline engine, all of these compounds are formedto varying degrees, and so generally when you're lookingat pollution reports, you see the general symbol NOX.

 

Now I think it's just a coincidence that this is also an abbreviationfor noxious, but what we're saying here is that the compoundsof nitrogen which are formed have variable ratios of nitrogenand oxygen because they consist of all of thesevarious combinations of gases.There is one last thing here as well.The one last thing is that Dalton also said there was one lastrule, and he turned out to be very wrong about this.He claimed that when 2 substances react, the simplestand most common compound will have the atoms present in the ratio of1 to 1.In other words, he thought that water had the chemical formula HO.And he argued this throughout his life, and was unable to acceptthe fact that water consisted of 2 atomsof hydrogen and 1 atom of oxygen.In fact, we know today that there is no substance which simplyhas the ratio of 1 to 1, hydrogen to oxygen, that is, has the chemical formula OH.One of the most interesting and controversial laws that cameup in this time period is called the law of combining volume, or also known as Gay-Lussac's Law.The law is actually a very simple one to state.It turns out that it's the volumes of gases that arealso important in chemical reactions.Now, Gay-Lussac was responsible for a law in whichhe determined that the volume and temperature of a gas are proportional.

 

We'll come back and study that later when we study the gas laws.So, it was determined that you could standardize the volumesof gas to a certain pressure and temperature.Once Gay-Lussac had done this, he recognized that this,of course, is not important in solids and liquids because they have a fixed volume.But here's the way the law works.The volumes of reactants are always in a simple ratio.What it means by that is that the volumes of 2 gases alwaysoccur not as a volume of 1.6 of 1 gas and 1 of the other, but in a simple ratio.Something like this:When we use the word, volume, here, what I mean is any measure of volume that you like.It could be a liter.It could be a cubic centimeter, or anything.OK, so what we see here is that 1 volume of nitrogen gascombines with 1 volume of oxygen gas to form 2 volumes of nitrogen oxide.Now the arithmetic works out fine here.One plus 1 equals 2, and nothing seems to be amiss,except we will see later that this goes contraryto what Dalton would have predicted.But this is not the only type of reaction that takes place.Another one is the reaction of hydrogen and oxygenforming steam or water vapor.Now this one, the arithmetic doesn't seem to work outat all, because here you have 2 volumes of hydrogen gascombining with 1 volume of oxygen gas to form 2 volumes of steam.Two plus 1 equals 2.The arithmetic doesn't seem to work.

 

Now, again, this is not mass, this is volume.But the volume relationships don't seem to work out aswell as you would expect them to.And even more strange, is the reaction of nitrogen and hydrogen to form ammonia.Here you have 1 volume of nitrogen gas with 3 volumesof hydrogen gas to form 2 volumes of ammonia.Notice, once again, that the ratio of hydrogen to nitrogen is asimple ratio; it's 3 to 1, it's not 3.2 or 3.4 or 3.79, it's 3 to 1.You also notice that in all of these reactions, all 3 of these,that the final product is 2 volumes.No matter what you start out with, you have simple ratios,but you wind up with 2 volumes of product in all cases.Now, Gay-Lussac didn't try to explain this.In fact, he didn't know how to explain it.Later on James Joule would say about this that it was oneof the most important discoveries ever made in physical science.The problem was at the time that it went contrary to Dalton's ideas.

 

Now I mentioned before that Dalton was kind of an authoritarian sort of guy.And Dalton, through his entire life, refused to acceptGay-Lussac's hypothesis because it went againstme--John Dalton!Dalton was a very authoritarian sort of guy and his rules hadsuggested that 2 volumes should produce 1 volume.In other words, that if you combine 1 volume of nitrogenwith 1 volume of oxygen, you should wind up with 1 volume of nitrogen oxide.And Dalton had said that if you combine 1 volume of nitrogenand 3 volumes of hydrogen, you should wind up with 4 volumes.I'm sorry, with 1 volume.So, here 4 volumes produce 1 volume.Now, again the arithmetic doesn't add up, but remember these arevolumes and their not masses, so we're not violating conservation of mass.The important thing is that Dalton argued that Gay-Lussac simplymust be wrong because it went against--me, John Dalton!He cast dispersions onGay-Lussac's experimental integrity.And this is very interesting because Gay-Lussac was knownall over France and all over England as well as a verycareful experimenter while Dalton was known as a "coarse" experimenter."Coarse" meaning, "you know, that's close enough, mix somethings together, it's pretty close, so it's close enough."It's interesting that Dalton had worked with these same gaseson a weight basis, weighing the product and the reactants.And it worked out the relative weight of the atoms involved in the processes.But Gay-Lussac was convinced that the resultsof his combining volumes aren't related to weights, but rather,he said, "They are characteristic of the gaseous state."So what we see happening here now is the laws of chemistryare giving way to something else which is the nature of matter in the gaseous state.

 

Now, here's part of the problem, too.Dalton was a believer in caloric.Remember caloric?This fluid of heat that surrounds the atoms?So, Dalton believed that the atoms were surrounded by caloric.So, if that's the case, how can you compress 3 or 4 volumes of gas into only 2?In other words, if you take the 4 volumes of ammonia plusnitrogen, how can you squeeze these together?The problem was that there was no reliable model for the gaseous state of matter.And in fact, the kinetic theory of gases which we'll take upin the next program was still 40 years away.This dispute between Dalton and Gay-Lussac was actuallyresolved in a simple, elegant manner in Dalton'slifetime, in fact, very soon after Gay-Lussac had published his results.This was done by an Italian named Avagadro.

 

Avagadro was an Italian of noble birth who actually started out practicing law.But because he was very interested in math and physicsactually wound up teaching physics at the University of Turin.He resolved this dispute in a very simple, elegant mannerby simply noting that equal volumes of gases at equaltemperature and pressure contained the same numberof particles--equal volumes of gases at equal temperatureand pressure contain the same number of particles.This is half of the law.By particles, he meant, the smallest unit of matter present in a gas.

 

Now, we know today that these may be molecules or they maybe atoms, but in Avagadro's time, the distinction between atomsand molecules and things were not that well understood.It turns out that some of the elemental gases like nitrogen,oxygen, chlorine and fluorine, are what are known as diatomic.One of the things that Dalton had not thought of in his rules wasthe possibility that 2 atoms of the same kind could combine with each other.What an elegant thing for Avagadro to think of this.The idea that 2 atoms of the same type could combinewith each other to form a molecule of a substance.So, what he's saying here is that the oxygen gas that we breathein the atmosphere is not simply atoms of oxygen, it's moleculesof oxygen, which consist of 2 atoms stuck together.So, he also as an outgrowth of this, recognized that this meansthat there are equal numbers of molecules in the products and reactants.It's not just that they're equal masses,but they're equal numbers of molecules.And I'll show you this a little later.It's interesting that the idea was not resurrected,not accepted, in Avagadro's time.In fact, it was a very obscure idea, and Dalton, of course,hated it, because it would have meant that Gay-Lussac was correct.The idea was resurrected in 1858.

 

It's apparent that Dalton's authority was a strong factorin this not being accepted, because Dalton simply wouldnot accept the fact, either that Gay-Lussac was correct,or the fact that 2 atoms of the same kind could combine with each other.There are other reasons, too.It's not just Dalton's authority.The theory of gases that was available at that time was astatic theory which pictured atoms or molecules of gasin contact with each other like fluffy balls of wool packed loosely in a crate.So, equal volumes of gases having equal numbers of moleculesrequired widely separated molecules, molecules that are not stuck together.Also, the cause of gas pressure in Dalton's time was thoughtto be the repulsion of one kind of atom of gas by another of like kind.That 2 atoms would not attract each other.That, in fact, 2 atoms would repel each other.And not only that, but the atoms of gas were thought to besurrounding by thick shells of this self-repulsive caloric.This is sort of like the wool, the fluffy wool.Remember the caloric theory.That gases were thought to be surrounded by large bags, if you want, of caloric.So, this is another good example.Avagadro's law is another good example of a theory very far ahead of its time.And we can see from this how the concept of caloric which was aparadigm, although incorrect, caused the rejection of a verygood explanation of something which turned out later on to be true.

 

 

 

Now we can use Avagadro's laws along with the atomic theoryto figure out the relative weights of atoms.You know this thing with Avagadro's or the diatomicgases, is sort of like you go to the store and you buy a packageof twinkies, thinking that you get 1 twinkie per package.And when you get home you find out that there's actually 2 twinkies per package.So, you actually have twice as many twinkies.And if you're trying to put together a picnic basketor something of twinkies, you wind up putting 1 twinkieinto each basket, so you get twice as many baskets as you thought.This is sort of the same idea of the diatomic molecules.So, along with this now, it allows us to find the correct formulasand calculate the atomic weights of various things.For example, if the weight of oxygen into weight of oxygenwhen the 2 gases combine is in the ratio of 8 to 1, and thevolume of hydrogen to the volume of oxygen is in the ratio 2 to 1,what does that tell you about the 2 weights?Well, I think we can figure that out if we go to the slide.

 

So, the idea is that you have oxygen combining with hydrogenin the ratio of 8 units of weight to 1 unit of weight.So, this implies that each oxygen atom must weight16 times as each hydrogen atom.I think you can see how this works if we take this step by step.So, if each oxygen atom weighs 8 weight units and the totalamount of hydrogen involved in the reaction weighs 1 weightunit, but that's distributed among 2 hydrogen atoms, so it's the ratio of 8 to 1/2.Because each of the hydrogen atoms weighs 1/2 unitof that 1 weight unit which combines with the 8 units of oxygen.So, proportionately we can say then, let's double the totalamount of the weight to look at the relative proportion.So that the oxygen weights has 16 weight units and the hydrogenhas 2 weight units, so, in other words, the 2 hydrogen atomsweigh 1 unit each and the oxygen weighs 16 units each.So, what we see is that if hydrogen weighs 1 unit,oxygen weighs 16 times as much, so we can say the relativeatomic weight of oxygen is 16 and the relative atomic weight of hydrogen is 1.

 

Now it turns out that this weight of hydrogen served as the basisfor atomic weights up until the 1960s when the atomic weightscale was redefined so that it was modified to useCarbon 12 as the base weight.OK.The interesting thing is that the relative weight of any atomwhich combines with either hydrogen or oxygen can bedetermined, and this is interesting because most atomswill combine with either hydrogen or oxygen or both.Let's go to the ELMO and I'll show you how this works.Let's get rid of this and get a nice fresh sheet in here.So it works something like this.We know that the ratio of oxygen to hydrogen is 1 to 16.In other words, each oxygen atom weighs 16 times asmuch as each hydrogen atom.We can go back to an earlier reaction where we saw thatlead and oxygen react in the ratio of 1000 to 77.We saw the ratio that 1000 grams of lead plus77 grams of oxygen forms 1077 grams of lead oxide.

 

Now, using the techniques developed by Dalton and otherchemists we can discover that the ratio of lead to oxygen is 1 to 1.In other words, the substance that we calledlead oxide has 1 atom of lead to 1 atom of oxygen.So what's the ratio of the weight then of each atom of lead?Well, I think we can see that, can't we?If we take these are in the ratio of 1 to 1,but the weight ratio is 1000 to 77.So, each lead atom must weight 1000 over 77times as much as each oxygen atom.So, how much does each lead atom weigh?It's about 13.It's actually 12.98.So, we can write here that each lead atom...I'm using thechemical symbol for lead...is equal to 13 times each oxygen atom.In other words, each lead atom weighs 13 times as much as each oxygen atom.So, what is the weight of lead then in relation to hydrogen?It's simply 16 times 13, isn't it?You can see this, you can do this algebraically.Let me slide this down a little bit.You can do this algebraically to note that if lead is equal to 13times "O," but "O" is equal to 16 times "H," then lead must beequal to 13 times 16 times hydrogen or, in other words, about 208.So each lead atom weighs about 208 times as much as each hydrogen atom.And if you look this up in your periodic table, Oops, I used thatword, we haven't got there yet, but we will.You'll find that sure enough the atomic weight of lead is 208.

 

Now it's time to turn our attention to the ideaof chemical symbols and equations.First I want to briefly review for you the rules of atomic theorybecause it really helps us to understand how theseatomic symbols and equations work.Matter is composed of atoms.Each type of atom has a certain weight and it's identical to allother atoms of the same element, or the same type.Atoms combine in certain proportions to form compounds.OK, so now we can look at the atomic symbols.The atomic symbols are really just shorthand notationsfor the names of the elements, and it's like any language where youevolve, like a mathematic language, even, where youevolve a way to talk about things without having to write out the entire thing.It turns out that the use of the atomic symbols is convenientfor lots of things, specifically, it's convenient for discussingchemicals and chemical reactions.

 

Now, most of these chemical symbols are logicalor mnemonic derivations of the names of the elements.If we go to the graphic, I think we can see how this works.For example, the symbol for aluminum is derived simplyfrom the first letters of the name, Al.The symbol for carbon comes from the C.The symbol for magnesium uses the mnemonic of Mg, like theMg, where the "g," of course, comes from the "g" in magnesium.You notice here that each of these is a symbol followed by, if thereare 2 letters, the second letter is a lower case.Now, several of these symbols are derived from the Latin or Greek names.And these are little bit harder to remember,but there aren't very many of them.This isn't all of them, but this is a large number of them.Iron, the symbol comes from the Latin word for iron which isFerrum, so we use the symbol, Fe.Sodium comes from the Latin word for sodium which is Natrium,which comes, so we wind up with the Na.Potassium comes from the Latin word Kalium.So we use the symbol K for potassium.Copper, well, it sort of works, starts with the right letter,but it's from the Latin word, Cuprum, so we use the symbol, Cu.For lead, we use the symbol, the Latin word, plumbum, and we use the symbol Pb.It's interesting here the word, plumbum, we don't use thatanymore for lead, but we certainly use the derivatives of that word.For example, we call the pipes in our house plumbing.

 

The word, plumb, in plumbing comes from the fact that thepipes in Rome were made out of lead.And, by the way, some people have suggested that might have beenpartially responsible for the fall of the Roman Empire.If you're using lead pipes, you're getting a lot of lead poisoning.We also use the word for a plumb bob.In fact we use the word plumb in the constructionindustry to indicate vertical.And the way we find vertical is to hand a lead weight and lookat the direction that the string hangs and call that plumb.So, we still use the words, derivatives of plumbumeven if we don't use the Latin itself.OK.There are certain conventions that are adopted.Those conventions have to do with how these letters are actually used.Keep in mind that each symbol is a capital letter followed by a small letter.Some of the early discovered elements keep only the firstletter, like carbon and what's another one, potassium, wasearly discovered even though it uses the Latin term.When you're talking about this, the first letter iscapitalized, but the element name is not.In other words, if you write the word, potassium, you don'tcapitalize the "P," but you do capitalize the symbol "K."We also use the symbol with the subscript to designate anuncombined element in the case where there are diatomic gases.And I showed you this earlier.For example, if we're talking about nitrogen gas, we use thesymbol, N with a subscript of 2, indicating that this is acompound formed of 2 atoms of nitrogen.

 

We also use other symbols for certain other substances,like the substances iodine and bromine, also occur as diatonicsubstances, and we often see those written as I2 for Iodine or Br2 for

bromine.The other thing we want to get into now is the idea of the periodic table.We'll come back and look at the derivationof the periodic table in some detail in a later program.But for now, it's important for us to understand that the periodictable is simply a listing of all the chemical elements whichcompiles in one place all the known chemical elements alongwith their atomic number, their atomic weight, and their atomic symbols.This organization also allows prediction of the chemicalreactions as we'll see when we get to that section on the periodic table.So now we want to turn and look at the idea of compound.Remember that Dalton talked about the fact that atoms couldcombine with each other in various proportions to form new substances.

 

The substances are called compounds and when we didthe program on the classification of matter, we lookedat specifically compounds as pure substances that contain only one kind of molecule.So, compounds are substances which arecomposed of more than one atom.Whether those atoms are the same atoms or different atomsdoesn't matter, they're still called compounds.The ratios of the various atoms in the compound are fixedby the chemical properties of the particular atom so that whenlead combines with oxygen, it combines either in the ratioof 1 atom of lead to 1 atom of oxygen or in the ratioof 2 atoms, of 1 atom of lead to 2 atoms of oxygen.We don't have any control over this, this is simply the chemical properties.The atomic symbols are also used to show the kinds of compoundsand the numbers of atoms that are involved in the reaction.For example, when you use the symbol, H2O, for water,we're indicating that water molecule, is a molecule madeof 2 atoms of hydrogen, 1 atom of oxygen, H2O.On the other hand, if we write 2H2O, we're indicating therethat we have 2 molecules of water, each 1 consistingof 2 atoms of hydrogen, 1 atom of oxygen.It's important to understand when we get to the derivationof chemical equations and the balancing equations that wecannot change the chemical structure.We can't change the H2O, but we can use different numbers of molecules.So we could use 2H20s or 3H2Os or 4H20s, or only 1 H2O.So now we can see also how chemical reactions take placeand how there are rearrangements of atoms to form new compounds.

 

Using symbolism of this type we can also see various otherthings like, for example, that mass is conserved.We can see the law of combining volumes,if we incorporate Avagadro's law into here.So, here, for example, we have a reaction I've written as 2H2 plus O2.This arrow means equal, but the arrow points in this directionmeaning that the reaction takes place in that direction,so we usually read this as yields to H2O.So what's happening here is we have 2 molecules of hydrogencombining with 1 molecule of oxygen to form or yielding 2 molecules of water.Notice how the symbolism relates to the picture.Each molecule of hydrogen consists of 2 hydrogen atoms bonded together.Each molecule of oxygen consists of 2 oxygen atoms bonded together.So you can see that what's really happening here is simply arearrangement where each of the hydrogen molecules is broken apart.The oxygen molecule is broken apart, and 2 hydrogen atomscombine with 1 oxygen atom to form a molecule of water.The other 2 hydrogen atoms form with the other oxygenatom to form a second molecule of water.So, what we're seeing here can be expressed also in terms of Avagadro's laws.Because here you have 2 molecules of hydrogen,and keep in mind that since equal volumes contain equal numbersof particles, these 2 hydrogen molecules would occupy 2 volumes of space.At the same time, the single molecule of oxygen would combine with, would occupy 1 volume.So here you have 2 volumes of hydrogen gas combiningwith 1 volume of oxygen gas to form 2 volumes of water.

 

Mass is conserved, everything is consistent, the chemicalreaction can be expressed either in termsof the symbols or in terms of the equation.In either case, it fits in with everything.So don't be scared by the term, Chemical Equations.A chemical equation is nothing more thana shorthand for describing a chemical reaction.It's better than writing out the entire thing.For example, we can note that iron reacts with sulfur to form iron sulfide.So, here's iron reacting with sulfur to form iron sulfide.Notice how much simpler it is and how much clearer it is to say itin symbolic terms than to say it in words.You'll also notice that the compound names are relativelysimple, if only 2 elements are involved.Here the naming is mostly consistent, and in this case,it's a sulfide because iron is combining with sulfur.So, if this was oxygen, it would be an oxide.If it was chlorine, it would be a chloride and so on.We'll get into some of the naming a little bit later in the program.We might also note that in many cases common names are given preference.For example, we would generally say water rather thandihydrogen oxide when we're combining water with anothersubstance or when we're using water in the chemical reaction.We'd still use the symbol H2O, but we would say the word, water.

 

One other thing is that in more complicated chemical reactions,other things are often added to the equation to indicatethe physical state of the substance.Here, for example is the reaction involving manganese dioxide asa solid which is mixed with hydrochloric acid in aqueous solution.In other words, dissolved in water to form manganese chloridein solution plus liquid water, plus chlorine given off as a gas.Notice how the symbols are used here."Aq" means aqueous solution, "s" means solid,"g" means gas, "l" means liquid.There might be other symbols that crop up from time to time,but these are basically the states of matter that are goingto enter into chemical reactions at any given time.Now it's time to take a look at how we useconservation of mass to balance chemical equations.If you've done this before, don't be too concerned about it.It's just looking at the amounts of things in each substance.And what we're looking at is simply the number of atomsmust balance on both sides of the reaction.I said if you've done this before don't worry, because you mighthave had a bad experience with this having to balance thesehorrendous equations like the one on the screen.But, we don't have to balance this one.All we have to do is look and see how this works.This is the equation we saw before using the subscriptsof solid, aqueous, liquid and gas, but now we notice a change.

 

Now we notice that there's a number 4 here, and a number 2 over here.All this is doing is telling us how much of one substance will react with the other.And we can see that this is balanced simply by counting upthe number of atoms of everything involved.Here, for example, manganese, 1 atomon the left side, 1 atom on the right side.Manganese is conserved.How about oxygen?Well, here's O2.This means that there are in this particular compound,there are 2 atoms of oxygen.If we look over here, what happened to all the oxygen?Well, over here is H2O has only 1 atom of oxygen, but there are 2 molecules.So, a total of 2 atoms of oxygen on both sides; oxygen is balanced.OK?What about hydrogen?Here there's 4HCl.Now here we have a molecule of HCl.This is a molecule consisting of 1 atom of hydrogen, 1 atom of chlorine.But we have 4 of them.So the total number of hydrogen atoms is 4.And sure enough, we look on the other side, and we have overhere, water, H2O, but we have 2 of them, so the total numberof hydrogen atoms involved is 4, 2 times 2.How about the chlorine?Over here we have 4 atoms of chlorine because we have 4 molecules of HCl.On this side we have the substance manganese chlorideis MnCl2, so that means there are 2 atoms of chlorine here,and the other 2 atoms of chlorine are given off as Cl2, which is a gas.So, we notice that we can change the numbers of things involvedhere, but we can't change the subscripts because theyrepresent the actual chemical elements.

 

Let's go to the ElMO and practice one of these.I need to get a clean sheet of paper here.The ELMO is here, OK, so.Let's look at this equation.We looked at this reaction before, but let's look at the reactionwhere we take hydrogen gas and combine it with nitrogen gas to form ammonia.How can we balance this reaction?We notice, first of all, that it is not balanced,because on this side we have 3 hydrogens and this side we have2 hydrogens, and on this side we have 2 nitrogens,and this side we have only 1 nitrogen.So, how can we possibly balance this?Well, balancing really isn't that really that hard,if we note something about the numbers 3 and 2.And I want to do a little thing here, just a little arithmetic thing.We know that 3 times 2 is 6.Everybody knows this.But we also know that this is equal to 2 times 3.What do the numbers 3 and 2 have in common?Well, they have in common that they, when multipliedtogether, they form the number 6.So, what does this actually mean?Well, 3 times 2 means that we have 3 rows of 2.Right?What does 2 time 3 mean?Well 2 times 3 means that we have 2 rows of 3.OK?Can you see that these two are actually the same thing?Because on one hand you can look at this as 2 rows...3 rows of 2.On the other hand you can look at it as 3 rows of...2 rows of 3.I'll get this right in a minute.On one hand you can look at it as 2 rows of 3;the hand you can look at it as 3 rows of 2.So, when you have the numbers 2 and 3, what does that mean?Well, if I take 3 of these and 2 of these, the number of hydrogen atoms is now 6.Three times 2 is 6, 2 times 3 is 6.What about the nitrogen?Well, on this side I have 2 nitrogen atoms combine in a molecule of nitrogen.On this side I now have 2 nitrogen atoms combined in 2 molecules of ammonia.So, add them up.Three times 2 is 6; 2 times 3 is 6, 2 times 1 is 2, 2 times 1 is 2,the equation is nicely balanced and everything is just fine.So, now we can turn our attention to the amount of substancesinvolved in reactions, and we'll do a little exercise with this in a minute.

 

Keep in mind that chemical formulas are showing us several different things.They're showing us the number of atoms involved in a reaction,but they're also showing us the ratio of atoms involved in a reaction.So, when we say the ratio of atoms involved in a reaction,that holds whether we have a lot of the substance or whetherwe have only a small amount of the substance.So we can look at this in several different ways.One way to look at this is to look at the term called the gram molecular weight.This is simply saying that you have an amount of a substancewhich has the weight in grams equal to the atomic weight of the substance.I think if we go to the computer slide we can see this a little bit better.Here, for example, is a balanced reactionof hydrogen and oxygen combining to form water.So, how much, what's the total weight of all the hydrogen involved here?Well, it's...each hydrogen atom has a weight of 1.There are 2 of them here, so that's a total of 2 times 1.There are 2 molecules, so we have altogether 4 atoms of hydrogen.So, the total atomic weight of 2H2 is 4.So in terms of gram atomic weight, we can thinkof 4 grams of hydrogen--1 for each hydrogen atom.In the oxygen gas, we have each oxygen atom weighs 16, relative to hydrogen.We have 2 of those in O2, so the total atomic weightof the oxygen is 32, so a gram

atomic weight of oxygen would be 32 grams.

 

You notice what happens here is that now we can see thatwe can combine our knowledge of atomic weight with the balancereaction to note that 4 grams of hydrogen reacts with 32 gramsof oxygen to form 36 grams of water.Notice that the equation is balanced.And sure enough, if you add up the total weight of the water,you find that you have 2 hydrogen atoms, at 2 each.You have 1 oxygen atom at 16 each, that's a total of 18--18 times 2 is 36.So, everything's balanced, and we see that 4 gramsof hydrogen produces 32 grams of oxygen.We have used 32 grams of oxygen to produce 36 grams of water.So, now we can pose a question.Given 16 grams of hydrogen, how much oxygen will combinewith it and how much water will be formed?Let's go to the ELMO and see if we can put this together.Another clean sheet of paper.So, here's the question.We're given 16 grams of hydrogen, and we want to combine itwith some amount of oxygen, and we want to know the resultof this, how much water will be formed?And, now, you may say, "Well, you know, who's going to make water, anyway?"But there are other chemicals that are made,and chemical engineers need to know this.So, let's go back now to our original picture whichwe saw that 4 grams of hydrogen will combinewith 32 grams of oxygen to form 36 grams of water.So, can you see now how to do this?

 

Notice here that this is like one recipe.For baking cookies, you use a certain amount of ingredients.So, if we're using 16 grams of hydrogen, this mustbe 4 recipes or 4 batches, right?So, how much oxygen are we going to use?Well, if we use 4 times the amount of hydrogen,then we're going to use 4 times the amount of oxygen.So, this must be 128 grams of oxygen.And now there are two ways to figure out how to finish it.We can simply add 16 and 128 to get a total of 144, or we couldlook here at 36 grams of water times 4.So, I'll bet if you multiply 36 times 4, you also get 144.4 batches--everything is multiplied by 4.Now you don't actually have to do this, but I think you can see howa chemical engineer can figure out exactly how much chemical theyneed to use in a processing plant to produce a certain amount of chemical.Now we can make a few general statements about naming compounds.The rules for naming are mostly systematic,and the name generally tells the composition.A few rules will help us to understand most substances.

 

Organic substances and more complicated substances we'll skip over.So, the simplest are simply compounds composed of 2 elements.Here we use the suffix"-ide" pronounced "ide" for the second element.Usually metals are written first and nonmetals, second.Some examples are hydrogen chloride, sodium chloride,carbon dioxide, potassium iodide.Certain groups of elements have a tendency to staygrouped during chemical reactions.They tend to stay together and so we give those special names.For example, SO4 is sulfate, SO3 is sulfite; NO3 is nitrate, NO2 is nitrite.Again, notice how the "ate" and the "ite" are usedfor the higher and lower numbers.In the same way, CO3 is carbonate and PO4 isphosphate, and CLO3 is chlorate.A couple of other ones, OH is hydroxide.Notice the use of the "oxide" there again, and NH4 is ammonium.There are also, we can look at the names of elementswhen there are multiple proportions involved.For example, suffixes "-ic"and "-ous" are attachedusually to the name of the first element.We can see some examples here."-Ous" is given to the element with the largest proportionor the largest number of atoms in the compound.For example, mercurous oxide is 2 atoms of mercury to 1atom of oxygen, but mercuric oxide is on the ratio 1 to 1.The same holds true for iron.Ferrous oxide is a higher number of iron atomsand ferric oxide is smaller number.Notice the use of the word, ferrous, ferric.Other prefixes such as "mono-, di-, tri-, tetra-,penta-" may be given to the second element.For example, carbon dioxide is CO2.Notice the use of the word, dioxide, whereas, CO is carbon monoxide."Mon" coming from the word, "mono" meaning one.On the same line of reasoning, SO3 is sulfur trioxide.And CL4, that's one atom of carbon, 4 atoms of chlorine is carbon tetrachloride.

 

Now there are other more complicated systems than this,but this is enough for most simple compounds, and for our purposesand understanding any kind of chemicals, except organicchemicals, this should be entirely sufficient.You don't have to memorize all the names, just go back and reviewthis and look at how the names come about, so that when youneed to, you can figure out what a particular chemical compound is made out of.In this program we tried to take you through the developmentof the atomic theory, which really brings us kind of full circlewith chemistry, at least for the time being.We still have some problems to consider.But we also looked at some stuff in this program of namingcompounds and that sort of thing, which I'm not suggesting youhave to memorize all the names of everything, but certainlydo be aware that these names exist.

 

The question I want to consider now for the next coupleof programs has to do with the atomic paradigm and the Newtonian paradigm.The question is, can these two things be reconciled?And we'll see in the next program that heat asa form of energy is really the link here.Because the atoms, after all, have mass, they're Newtonian particles.So, the question is, if they're Newtonian particles, they dohave mass, do they obey the laws of mechanics?Can we apply Newton's laws somehow to figure out how this fits together?And I think, in the next program, we'll be able to do this very nicely.So, I think that's it for Program 25.So, remember, when it comes to science, get physical.Bye.Silico: "Do I have to know all of those names?How come I never get to say "Get Physical?"Hey, I just said it, get physical.Bye."Music