as scientists have done experiments and learned more and more about atoms they've changed the way they think about atoms so in this video we're going to look at a timeline of the different ways that scientists have pictured or imagined atams over the years now the first people to really talk about the idea of atams were the ancient Greek philosopher democratus and his teacher liuk kius they lived about 2,500 years ago and democratus he said something like this he said imagine you have an object like say a slice of bread and you cut that in half and then you take half of that and you cut it in half and then you take half of that and you well you get the idea eventually he said you're going to come to something that you can't cut in half anymore and he called these objects he called them utmos which means uncuttable and it's where we get the word atam from democratus imagin that all matter all stuff was made of these tiny uncuttable particles and he imagined that the atoms came in different sizes and different shapes he imagined for example that iron atoms had hooks which is how they could hold together so strongly and he thought that salt atoms had spikes on them because he felt that salt tasted Sharp so democratus was right but people didn't really take to his ideas part of the reason was because around the same time the well-known philosopher Aristotle proposed his own idea of what matter was made of he said that different things were made of different amounts of the elements earth water air fire and ether this is kind of like Captain Planet if you're old enough to get that reference and more people believed Aristotle maybe just because he was so popular already so democratus and lippus they were right all along but here's the thing they weren't scientists they couldn't do experiments in the laboratory to prove that they were right and because of this some people think that their idea it was just kind of a lucky guess they couldn't actually prove what they thought so you know how can you tell whether it's right or wrong ideas about Adams remain that way for about 2,000 years until in 1808 the British chemist John Dalton came up with the first scientific experiments that showed that matter was made of tiny little particles this is kind of how John Dalton pictured Adams he imagined them sort of as tiny little balls that arranged in different combinations to make different things and he imagined that these atoms were indivisible you couldn't cut them into smaller pieces now at first nobody believed Dalton but over the course of the 1800s more and more scientists did begin to believe what he had to say but then in the 1900s the early 1900s people's idea about atams started to change one of the key things that caused this change was that in the late 1800s JJ Thompson discovered that atoms have electrons and he discovered that electrons are much much smaller than atoms so while Dalton thought that atoms were tin indivisible JJ Thomson said no no no they're not indivisible because they're made up of electrons which are much smaller so JJ Thompson pictured the atom as sort of like a blueberry muffin he called this The Plum Pudding model JJ Thompson imagined that if you took an atom and split it open you'd see Tiny electrons stuck throughout the inside of it just the way blueberries are stuck in the dough of a blueberry muffin and Thompson thought that what's the dough in a blueberry muffin that it was like a positively charged substance so you had negative electrons stuck in like a positively charged dough and together the positive and negative charge balanced the the two things Balan balanced each other out so that the atom was electrically neutral but the big change from Dalton's model to Thompson's model was showing that atoms weren't actually indivisible that they were made of even smaller things now not too much longer in the uh gold foil experiment Ernest Rutherford discovered that atoms had a nucleus that all the positive charge in an atom was concentrated right in its Center and that besides that and the electrons atoms were pretty much empty space so JJ Thompson thought the positive charge was all distributed throughout like dough and a muffin but Rutherford showed that all this positive stuff was concentrated right here in the center and this is what we call the nuclear model of the atom because it has a nucleus sometimes people call this the Rutherford model now so far we've been talking a lot about the positive charge and the nucleus of an atom but we haven't talked too much about what's actually going on with these electrons in the atom and in 1913 the physicist Neils bore came up with his model of the atom he reasoned that there was a nucleus in the middle just like ruford had but that electrons instead of just sort of being randomly distributed throughout the atom bore said that the electrons were sort of like planets around a sun that they were spinning around the nucleus in circular orbits so here a picture of some of the electrons and here are the orbits imagine that they're spinning around the nucleus in these circles all right now people thought B's idea for the electrons made a lot of sense at first but then in the 1920s additional experiments showed that it wasn't exactly the way electrons really move and a variety of physicists particularly the physicist irn schinger showed that electrons weren't really spinning in orbits but it's more like they were hyperactive flies and they were buzzing around the atom sketching out different shapes it's kind of if you did like timelapse photography on a hyperactive fly and you saw that over a long period of time it sketched out a particular design and whereas bore called these circular paths he called them orbits schinger called the hyperactive sketch out shapes he called them orbitals here's a circular orbital too but electrons didn't only make circles this is actually a sphere because it's a circle in three dimensions here is another shape another type of orbital that electrons could also make looks like this sort of two tiar drops next to each other so in the quantum mechanical model electrons don't orbit the nucleus they Buzz around the atom sketching out different shapes now let's focus on the nucleus here over the same amount of time and a little bit later scientists were discovering the two subatomic particles that make up the nucleus so we can refine this picture a little bit more in 1919 Ernest ruford discovered protons there they are and then in 1932 James Chadwick discovered neutrons so the really correct view of the quantum mechanical model shows the orbitals being sketched out by the electrons but then also shows the subatomic particles protons and neutrons here in the nucleus now this is pretty much how we think about atoms today but as scientists learn more and more about atoms as they do more experiments they're going to find that this model isn't exactly a perfect representation of what atoms are really like and they're quite likely to change this and refine it even more now as I said this quantum mechanical model is like the really accurate way to describe atoms but the thing is with these orbitals it can really be kind of a pain sometimes to describe simple things that atoms are doing using electron orbitals and so a lot of times in these videos when I talk about atoms I'm actually going to be sort of using a cross between the very correct quantum mechanical model and the sort of outdated B model just because for our purposes a lot of the simple things we're going to be talking about the bore model it works works just fine so already you've probably seen me draw atoms like this where you see the the electron orbits at different angles and sometimes particularly when we're talking about bonding we're going to be drawing atoms like this with the protons and neutrons here in the nucleus and then electrons in different rings different orbits on the outside of the atom we're going to find that thinking about the atom like this is very useful for simple tasks talking about bonding and stuff but keep in mind that when we're discussing atoms they actually aren't exactly like this and they're much more like the quantum mechanical model so keep in mind that I'm lying to you a little bit but I'm lying to you in order to make it easier to convey some fundamental topics