 All right time for the entirely oversimplified yet totally sufficient history of atomic structure Now we did these timelines in class and you had to make and fill out these tables About the history of atomic structure in class, but I saw a lot of mistakes on So I'm putting this video up so you can go back through Figure this stuff out because I'm not teaching it in class We just don't have the time especially with the snow day or days that we have coming up So let's take a look at it and really dates aren't so much as important as it is people and what they did you got to know the The people the particles the laws the theories the models the experiments and stuff like that So the whole thing starts in 460 BC fifth century BC with Democritus Democritus is the first person that suggests that Adams exist. He's the first person that came up with the idea of an atom. His idea was simple Take a piece of lead cut it in half Take one of those halves and cut it in half Take one of those halves and cut it in half. You keep getting smaller and smaller pieces of lead he Came up with this idea that you would reach a point where it was so small If you cut it in half again, it wouldn't be led anymore You would have an atom most of lead which is great for Adam You have an atom of lead and if you split that atom in half It wouldn't be led anymore despite the fact that he's the fifth century BC was that long ago that idea is really correct That is what Adams are. It's the smallest particle of an element you can have if you break it down any further Then it's no longer that element anymore. So that's Democritus. He's the one that starts it all Now this timeline that I'm using this is a simplified one I used in classes before does not include Lavoisier and Proust they fit in this segment in here in 1774 in France We have Lavoisier and his idea was the law of conservation of mass What he did is experiments with chemical changes and what he noticed is that the mass of the reactants was always the same as the mass of the products So if you started with a candle in a jar Unlit just in a jar And it's mass was I don't know 35 grams You can light that candle let that candle burn down as long as it stayed in the jar and you captured all the gases that came off That candle candle might look smaller. There might be less candle there But if you account for the mass of all the gases that are produced as well It would still be 35 grams. There would be no change in mass He fits in here right after Democritus in 1799 Also in France we have Proust and Proust writes the law of constant composition What he did is he did chemical reactions on compounds and broke them back down into elements again So for example, he took carbon dioxide he could break it down into carbon and oxygen He took water you can break it down into hydrogen and oxygen And what he found is no matter where that carbon dioxide came from it was also always the same ratio of carbon and oxygen by mass Wherever that water came from didn't matter where that water came from when he broke it down It was always the same ratio of hydrogen to oxygen by mass That whole We talk about percent composition thing the percent composition was the same no matter where that water came from That was Proust's Contribution about these take place in France and here's a little interesting cross-curricular thing Notice we go from France to England with Dalton and Thompson and Rutherford these people all worked in England the switch Was the cause of the French Revolution When these guys were doing their science they were funded by the monarchy of France when the French Revolution happened they ended up in jail some of them ended up losing their heads for it and That was the end of the French contribution so to speak as the Revolution took place people were more worried about survival than they were about science So from there it moved on to England and we see a lot of development taking place in England instead picks up with Dalton 1808 what he does is the first atomic theory He doesn't know what Adams are and that's the interesting part here but what he does he takes all these ideas that came before him and he puts them together into What are four major points in his atomic theory? First of all all matters composed of tiny particles called Adams basically democracy's idea there The second idea is that Adams of an element are identical and different from every other element In other words if you had a sample of gold Adams you had a Mole of gold 6.02 times 10 to the 23rd Adams of gold What he's saying here is that all the gold Adams would be the same but those gold Adams we'd different from every other Gold Adam so a interesting idea. He's also saying they're different from every other Adam of every other element So if you had a mole of silver Adams all those silver Adams would be identical But they would be different from every other Elements it'd be different from the gold Adams all the gold Adams are the same All the silver Adams are the same But they're different from one another. That's what he's getting to there The third thing the third point Adams combined and fixed ratios to produce compounds Good old Prost was doing here this constant composition idea. He's talking about how the Adams of an of The elements they should say because Prost wasn't talking about Adams The elements are always combined together in the same ratio So you always have the same ratio by mass of carbon to oxygen and carbon dioxide what Dalton's saying well That's because you have the same elements You have the same Adams combining in the same ratio. So that's democracy's idea. That is Prost's idea Fourth and final thing he says is that Adams are not created or destroyed in chemical reactions They're rearranged That's the Vossie's idea in action He's just applying the idea of Adams to it. So really these four things only the second one is Really his idea this idea that Adams of an element are identical but different from other elements when he says matters composed of Adams democratists Had already come up with that idea This is Adams combined and fixed ratios to make compounds. That's Prost's idea constant composition The ratios by mass were the same because the Adams and their ratios were the same And then Adams can't be created distorting chemical reactions That's just building on the Vossie who says mass cannot be created destroyed The reason why mass can't be created destroyed is because Adams can't be created or destroyed So again that idea here about elements of the Adams of an element being the same but different from every other element That's his big contribution to all of this now. He had no idea what Adams were We don't get anything on that front until JJ Thompson comes along in 1876 he's working with cathode ray tubes glass tube electrodes at both end beam shoots down the middle He's trying to figure out the beam was made of so he does some experiments with it with Electrical fields around it to see how it reacts to electrical fields He puts paddle wheels inside to see what it does to paddle wheels He comes up with this idea that those that beam is matter and it's a part of an atom and that part of the atom Is the electron that's what he discovers he discovers the electron It's the first piece of the opomic puzzle now It gives us the ability to go back to adult and saying here and try to get some more detail in it So we can start thinking about what an atom is And that's where it comes up with the plum pudding model of the atom This idea that you have this massless cloud of positive charge with the electron scattered around through it now It's named after plum pudding because the idea was and in a plum pudding you've got this bread This bread is the massless cloud of positive charge. You've got these raisins or prunes in it these these dried up plums and Those would be the electrons scattered through it best way to think about that's the chocolate chip cookie model Where the cookie is the massless cloud of positive charge and the chocolate chips are the electrons scattered through it There is only one particle because that's all he knows Electrons this is attempt at explaining what an atom was In 1911 we get the next It's in pieces of information from Ernest Rutherford He's doing the gold foil experiment radioactive source shooting radioactive particles had a thin piece of gold foil He knows most went straight through that most went through the gold foil like there was nothing there some Deflected off in different directions something can bend them or change their path Well, if you were still bounced right off of it Based on those observations he came up with the idea the nucleus This thing that was they were bouncing off of these particles were bouncing awesome had to be something They had a relatively large mass, but was relatively small because not many of them bounced off So this small massive object the center of the atom called that the nucleus This deflection here Had to do with the nucleus charge He knew these particles that he was shooting at it were positive and what he theorized is that they were being repelled by positive charge So that nucleus that he discovered must have a positive charge Meaning it must contain a positive particle. He called it the proton. So Rutherford discovers the proton and the nucleus When he does his gold foil experiment The nucleus is this compact mass of center of the atom and it contains these positive particles called protons He just ideally thought that this must work kind of like a solar system with these electrons, which were negative corn Thompson Orbiting that nucleus called a planetary model. So big big change for the plum pudding to the planetary Believe it a little solar system instead of a sun in the middle. There's a nucleus in the middle Instead of planets orbiting it you got electrons Orbiting it instead of gravity holding the whole thing together. It's opposite charge negative electrons being attracted to a positive nucleus Next up and the dates vary in the and some of the things I've researched it puts Chadwick at 1932 and it's put Neil Bohr and his work at 1922 this one here is talking about 1940s You know, whatever as long as you know what they did. That's what's more important James Chadwick Fixed a problem with this model when Rutherford came up with a model he stuck all these nucleus There's protons together in the nucleus and these protons have a positive charge and like charged objects repel each other So all these positive charges shouldn't be there together They should be repelling each other. So there has to be something in there that's stopping them from repelling The second big issue with this is that the masses didn't work when he took his model and he tried to predict the mass of elements It was always less than what they really were by about half So there had to be something else in there Chadwick discovers something else He discovers Neutrons the other particle that's found in the nucleus the neutral particle that's found in the nucleus little trivia Jimmy neutrons named after James Chadwick Nickname a very common nickname for James is Jimmy Jimmy discovered the neutron and that's where the whole name came from that might help you remember it So I guess it's more than just trivia. It'll help you remember stuff for the test Finally last person on this timeline again kind of comes here on some timelines when you look at them online when you try to research this stuff sometimes comes after Meals board Another problem with this model is that orbiting bodies eventually crash into whatever they're going to orbit But these electrons never crash into the nucleus So they can't be just orbiting it. There has to be something Different about it. He uses line spectra, which we'll talk a little bit about in class because it's important and and based on this line spectra comes up with this idea that The electron cloud this outer part is not just a willy-nilly electrons orbiting the nucleus thing that the electrons have to Exist at very discreet distances from the nucleus. They have this as the nucleus. It has to be here Here or here. It can't be anywhere in between He called these discreet distances energy levels Basically, he comes up with the idea of dividing up the electron cloud the outer part of the atom into energy levels That's his big thing So what do you need to know? Democrat is the first person that came up with the idea of the atom La Voce is a person that comes up with the law of conservation of mass That the mass and the chemical reaction never changes the mass that react and some products are always the same Prouce law of constant composition The ratio of elements by mass is always the same in a compound no matter where it comes from So if you took carbon dioxide that you exhaled versus carbon dioxide from dry ice versus carbon dioxide from burning something And you did the percent compositions the answers would be the same no matter what the percent of carbon would always be the same No matter where it's from percent of oxygen would always be the same no matter where it's from That's his idea Dalton comes up with atomic theory the first atomic theory takes the ideas of Democritus and La Voce and Proust and combines them together with some zone ideas into the first uniform theory of what atoms are He's considered the father of modern chemistry for that reason it changes the focus of chemistry towards atoms Which is where it stayed ever since Know the points of its atomic theory Thompson does the cathode rate to Experiment in that experiment discovers the electrons The negatively charged subatomic particle very small one is going to learn Based on that it comes up with the plum pudding model of the atom Rutherford doing the gold foil experiment Discoveres the nucleus of the atom the small densely packed cluster in the center where most the masses and In that nucleus he says there are protons positively charged particles Those are his two biggest discoveries the protons the fact that there's a nucleus in an atom And on to Chadwick Does the same gold foil experiment by the way? He's actually just using Rutherford's experimental data He was a graduate student of Rutherford's So same experiment, but in that experiment figures out the neutron idea the other particle that's in the nucleus It ends up being equal in size to the protons, but it has no charge And then finally Nils Kind of changes the way we look at that electron cloud that outside of the atom No longer do the orbit, but they exist within energy levels. It divides the electron cloud up into energy levels These discreet distances from the nucleus where those electrons have to exist so go back to that That that table sheet that I'm going to give you back Fix the stuff you need to fix the biggest things are what they discovered when it comes to Thompson Rutherford Chadwick and Bore those four people there are a lot of mistakes on the timelines in terms of what they did what they discovered I Saw a few of you the left off the fourth point. It was on a separate slide You just had a look at the next slide down to find point four But a lot of you didn't have point four on there, so make sure you got it fix it study it This is what you're going to be quizzed on