[Music] hi and welcome back to free science lessons by the end of this video you should be able to describe the plum pudding model of atomic structure you should then be able to describe how the results of the alpha scattering experiment led to the nuclear model now the idea of atoms has been around for a long time thousands of years ago the ancient Greeks believe that everything is made of atoms they believe that atoms are tiny sphere which cannot be divided and that idea was accepted for hundreds of years now in 1897 scientists discover that atoms contain tiny negative particles which the scientists called electrons the discovery of electrons told scientists that atoms are not tiny spheres that cannot be divided instead atoms must have an internal structure scientists now suggested a new model for the structure of atoms and they called this The Plum Pudding model I'm showing you the plum pudding model here in the plum pudding model an atom is a ball of positive charge with negative electrons embedded in it this is what an actual Plum Pudding looks like so you can see where the name came from now scientists wanted to know if the plum pudding model was correct to find out they carried out an experiment called the alpha scattering experiment and you need to be able to describe this now the alpha scattering experiment is one of the most important experiments in science and that's because it radically changed the way that we think about atoms first the scientists took a piece of gold foil just like this one they used gold because we can Hammer gold into very thin foil just a few atoms thick scientists then fired tiny particles at the gold foil we call these alpha particles and you'll find out more about these in physics the key fact you need to remember is that alpha particles have a positive charge the scientists found that most of the alpha particles pass straight through the gold foil without changing direction like this sometimes an alpha particle was deflected in other words it changed direction as it passed through the gold foil and sometimes an alpha particle simply bounced straight back off the gold foil like this so let's look at what the scientists work out from these results now the fact that most of the alter particles went straight through the gold foil told the scientists that atoms are mainly empty space so straight away they knew that the plum hudding model had to be wrong secondly because some of the alpha particles were deflected this told the scientists that the center of the atom must have a positive charge remember that alpha particles are positive so any alpha particle that comes close to the positive center of an atom is repelled and changes Direction and finally because some alpha particles bounce straight back this told the scientist that the center of an atom must contain a great deal of mass We Now call the central part of an atom the nucleus so from these results scientists replace the plum pudding model with the nuclear model I'm showing you the nuclear model here most of the atom is simply empty space in the center of the atom we have a tiny positive nucleus containing most of the mass of the atom and around the edge of the atom we have negative electrons so as you can see new experimental evidence led to the plum pudding model being replaced by the nuclear model in the next video we look in more detail at the nuclear model of atomic structure you'll find plenty of questions on this topic in my vision workbook which you can get by clicking on the link [Music] above [Music]