in this video I'm going to talk about some early models of the atom that I want you to be familiar with in in this course the first one that we'll reference is John Dalton's model uh and John Dalton put forth what we call the first formalized atomic theory it was in the early 1800s and we call this the first formalized atomic theory because we actually attribute the first ideas about the atom to the Greeks which about 2,000 years ago um there was a Greek philosopher named democratus and he um sort of thought about if he's looking around him and sees a rock and he thought well what happens if I chop this rock up into smaller pieces and smaller pieces and smaller pieces at some point I would get to uh a point where I can no longer chop that rock into any smaller pieces and at that point um he coined that phrase atomos so atomos is um is that the Greek term that was used to think about what we would uh call something if I took any object around us and chopped it up into smaller smaller pieces and got to that point where we can't chop it up any further uh when the Greeks were thinking about atoms and thinking about matter they were really philosophers not scientists so they had these ideas but they didn't do any follow through with them so they weren't actually going around chopping up um chopping up substance and checking to see do we get to that point where I I can't chop it up any further um but they were thinking about things they did a lot of we call thought experiments John Dalton is the first one this formalized atomic theory the first one to really put forth this kind of nice package of um of how we can use these Atomic ideas to explain the changes that we see around us um and they were his ideas were based on experiments and observation and data and tested over and over again so these are things that we um now recognize as sort of foundational to Atomic Theory John Dalton's atomic theory um has a number of statements I have a few of them here um the first statement is that matter is composed of tiny indivisible particles called atoms and that's not unlike what the Greeks were saying right the Greeks were saying that if if I take a rock and I I chop it up then I get this smallest indivisible particle of the rock Dalton also said that all atoms of a given element are identical um so if I have a hydrogen atom every hydrogen atom is going to be the same um and then uh a third statement here is that all atoms of uh one element I have a little typo there of one element are different from atoms of any other element so if I have a hydrogen atom that's going to be different from a carbon atom or uh an oxygen atom he has several other statements that go along with his uh his early model that he put forth and we'll talk about those in uh additional chapters so they have to do with how atoms are going to combine uh to form compounds but we have three statements here um and so that first one that that matters composed of tiny indivisible particles so that's one I want you to think about in terms of just kind of visualizing what this earliest model looks like so um when I think about Dalton's model I just think about a solid sphere the important piece is there's no internal structure there are no protons electrons neutrons there just was not the any technology for us or for him to to see any of those things or observe any of those particles so a hydrogen um atom might like look like this and then we could represent maybe a an oxygen atom like this or if you see pictures of his drawings you'll see that he used different shapes for different at so um so the atoms uh are are indivisible meaning they don't have any uh any internal structure the second model that I want you to know um was put forth by someone named JJ Thompson so this was around 18 997 so toward the end of the the 18th century um so in JJ Thompson um his big contribution the big change that he made was the having some inter internal structure to our atom so I do want you to recognize um not only what each of the models are but how um what was the the big gamechanging thing from one model to the next so the big thing that happened from Dalton's model to Thompson's model is that we now do have an internal structure so Thompson was able to discover that these particles um could stream out from uh a sheet of metal so we would have these particles uh which he called electrons so his model basically is involving a positively charged sphere so we don't have positive particles but the whole kind of sphere is positively charged and then we have these negatively charged particles um that are kind of embedded if you will in that positively charged sphere so the overall atom is neutral because the positive sphere and the negative particles are going to cancel charge um but the negative particles are kind of embedded in that um that positive sphere so the change we have with Thompson so he discovered the electron so that's the the big piece that I want you to know this is sometimes called the plum pudding model and that's kind of an old name for it so Plum Pudding so Plum Pudding is a a British uh kind of dessert where it's like a cake and it's got nuts and berries and things inside um I like to sometimes think of it as a chocolate chip cookie so in the chocolate chip cookie like the cookie part would be the positively charged sphere and then the chocolate chips would be the electrons so that's a plum pudding or a a chocolate chip cookie model the third uh model that I want you to recognize is um attributed to Ernest Rutherford Rutherford was actually a student of of JJ Thompson so worked in his lab at his university um and Rutherford did a lot of things related to the atom if you go on to do any more um Atomic chemistry or Atomic physics um you'll learn a lot about Rutherford's contributions uh during this time um he discovered different forms of radioactivity he used one form of radioactivity which is uh the alpha particle and so we have an alpha particle is basically uh what you need to know about this is a positively charged uh particle and sometimes we call it a helium nucleus so it's basically just two protons um and and two neutrons so it doesn't have any electrons so it's just a positively charged particle and this is a a form of radiation um that can be emitted from a radioactive substance so one of the things that Rutherford and his team did was set up an experiment called the gold foil experiment and the gold foil experiment looks something like this um he basically took a r radioactive substance and emitted this is a particle emitter here he emitted these alpha particles so he's going to shoot these positively charged particles at a gold foil so this little piece right here this is like a very very very sh very very thin sheet um of gold you can think like an aluminum foil sheet but much much thinner um so the thickness is just a couple of atoms thick so this really really thin uh foil of gold and we're shooting these uh positively charged particles at them on the outside here this kind of ring this is basically a detector so the detector is going to light up anytime an alpha particle hits it so if there was nothing there if we're just shooting alpha particles straight through the alpha particle would go here it hits the detector and it's going to make a little flash of light so if there's any deflection of the alpha particles right if if they don't go straight through then we would see them on various parts of the screen so this is a setup for the the the gold foil experiment and we have here uh two pictures I pulled from your book and so these two pictures um kind of test the two different ideas so this is Thompson's model and then this one over here I'll just call this one number two for right now so for Thompson's model if Thompson's model which is this one right up here we have the positively charged sphere and then the negative little particles um so here's our sphere this is our positively charged sphere and then these little guys here these little green ones these are our electrons so if we're shooting in so in the gold foil experiment we're shooting in these positively charged particles if we shoot these through our gold foil um there's nothing big for them to interact with right so this this particle is going to go through this alpha particle is going to go through this one is going to go through this one um is getting deflected just a little bit but for the most part uh we would expect if we use Tom Thompson's model that the alpha particles would just go straight through that sheet and so if they went straight through the sheet most of the um the hits on the uh the detector screen should be in this region here you might have a little bit of deflection as the the particles get pulled toward a a negatively charged particle but we should see everything pretty much here what happened if we look at this one what happened when they shot the alpha particles at the gold foil is that we did have some that were here but we had some that had a a big deflection maybe this way and there were some that actually got deflected back so back toward the detector and so with Thompson's model this should not have happened you shouldn't have had any um of these positively charged particles go into your your gold foil or hit a gold atom and bounce back backwards and so the the gold foil uh experiment provided evidence that that this model was not correct so the evidence did not support that model and so a new model um had to be presented and the new model that was presented is what's known as the nuclear model so in the new model we have still our here's our uh our atom but instead of that whole kind of yellow goldish piece having a positive charge kind of spread out across the whole thing now we have the nucleus and all of that positive charge is concentrated In This Very dense central region of the atom so when these positive uh alpha particles go through most of them just kind of shoot right through and don't touch anything but if we have one that hits right at that positively charged nucleus because this is positively charged and these are positively charged we know two positively charged things will deflect each other then we would have this really big deflection of that uh of that alpha particle and so Rutherford's kind of gamechanging piece the thing that that changed with his model relative to Thompson's model is that now we have we still have our our little atom we still have the electrons but now we have a nucleus so as I go from Thompson to Rutherford's it still had those little electrons I'll still just these are still kind of out wherever wherever they want to be um but this is called the nuclear model so the three models I want you to know from early early on we have Dalton which is just a kind a solid sphere no internal structure there's Thompson who had the plum pudding model which gave us the electron and then there was Rutherford who had the nuclear model and that gave us the uh the nucleus the next model that's coming which we'll talk about in just a um a few days or maybe a week um is the uh the bore model so the bore model is the the next model that we'll look at and then after that we'll get into the quantum model