in today's video we're going to run through the history of the atom so we'll take a look at some of the different scientists that have contributed theories and see how their experiments influenced our understanding of the atom and how its structured the first major theory that had tried to explain what stuff is made out of was atomic theory which is the idea that everything is made up from tiny little particles that can't be broken down any further and that they're separated from each other by empty space this was originally proposed by a guy from ancient greece called democritus who was alive around 500 bc it then took another 2 300 years meaning the 1800s before anyone really improved on his ideas at this point john dalton described atoms as solid spheres and importantly he suggested that different types of spheres might make up the different elements a short while later in 1897 j.j thompson came up with the plum pudding model he had done a series of experiments which showed that the atoms simply couldn't be solid spheres and instead that they must have contained negatively charged particles which we now know to be electrons so using this new evidence he proposed that the atom was a general ball of positive charge with discrete electrons stuck in it just a few years later in 1909 a man called ernest rutherford and his students made another big discovery what they did in their experiments is they took positively charged alpha particles and they fired them at a really thin sheet of gold the idea was that if the positive charge in the gold atoms was generally spread out as jj thompson had proposed with his plum pudding model then the alpha particles should pass right through the sheet of gold because the weak spread out positive charge wouldn't be strong enough to affect them weirdly though what actually happened was that some of the alpha particles were deflected to the side and a small number were even deflected back the way they had come proving jj's theory wrong because of these results rutherford suggested his nuclear model which proposed that instead of a general field of positive charge there was some sort of compact nucleus which contained all the positive charge of the atom and he thought that the negative charge must exist in some sort of cloud around this central nucleus at this point rutherford was already pretty close to how he currently understand the structure of the atom but his model had one important flaw namely there didn't seem to be anything stopping this cloud of negative electrons from rushing in towards the positive nucleus meaning that the atom should just automatically collapse which we know it doesn't just four years later though in 1913 a man called niels bohr suggested a solution he suggested that the electrons orbited the nucleus in a similar way to how the planets orbit the sun and also that they were held in shells this idea was really important because the orbiting of the electrons is what prevents the atom from collapsing in the years since then many experiments have supported this model and it's pretty much the same one as we followed today with just a few small changes further experiments by rutherford found that the positive charge in the nucleus is actually made up of small discrete particles which we now know as protons and a short while later a guy called james chadwick provided evidence for neutral particles in the nucleus which we now call neutrons and that's pretty much how we understand the atom today anyway that's everything for this video so hope that was useful and we'll see you next time