Hello, my team and I have been asked to create a video to help you with an area of your first year physics course. We have decided to cover types of bonding, cohesive energy calculations and crystal defects. These topics form part of your thermal physics course and we hope that you find this helpful if you are struggling. The properties of matter segment of this course is often underestimated by students, myself included and hopefully this video gives some way to resolving your issues. Before we get down to the physics it's a short clip of me using phenathosalicate powder to make some crystals to show you the applications of what we are going to tell you about. If you were to look at these crystals through a microscope you would see a lot of what we have described in this video. After this James will talk to you about types of bonding. So let's go over the basics. What are the types of bonding in crystallized structures? What to start with we have covalent bonding, characterized by the shane of electrons between atoms. In our example here we have covalent atoms showing four electrons to form diamond crystals. Secondly we have ionic bonding. In our ionic bonding we have atoms that give over electrons to other atoms. For example here we have sodium which gives an electron to chlorine, forming a negative and a positive ion which attract each other, forming a diorionic crystal lattice. For example here we have NACM, like we have metallic electrons. Now metal atoms are special because they are out of the electron shell that is free to move within the solid. There is therefore a electrostatic force of attraction between this sea of three electrons and the positive metal ions. We have got an example here, we have copper. Finally we have found the valescent interactions. These happen between molecules and atoms where there is a redistribution of charge forming a diol across the molecule that we have posted on negative N and these are attracted to each other following a bond. These are normally very weak and normally happen between gases at the real temperature, like sea otters. The types of bonds in the material, in the position of each atom or ion within the solid, they are having a very important property which is cohesive energy which is defined as the energy required to separate all atoms to infinity. To calculate them we need to think about each individual particle within the material. So we think about the potential energy per atom, U. U is a function of R0 where R0 is the minimum distance between two atoms in the material so it is the equilibrium distance. The cohesive energy per atom will be negative that so it is cohesive energy per atom equals minus U. To calculate the potential function at our node we need to think about which bond is keeping the solid together. So if it is an ionic bond we will use a coolant interaction form. If it is covalent bonds we can use our most potential. If it is van der Waals bonds we can use Lennard Jones potentials. If we have a metal we need to think about many body interactions model that deals with the position of each atom and ion and the ionism between them. So here is an example on how to calculate cohesive energy for a material. This is a material that is arranged in simple cubic structure. So there is a cube and the atoms are each corner and their minimum distance are not and that is the nearest neighbor distance. So if we think about the atom the nearest neighbors would be at distance R0 and there is 6 of them and the second nearest neighbors would be at a distance root 2 for that node. There would be third nearest neighbors as well and fourth nearest neighbors as well but we need to think about how strong the bond is. So if we have an interaction that only affects the first nearest neighbors we calculate the cohesive energy of the solid by thinking about the potential energy per atom potential at R0. Times the van der Waals neighbors which in this case is 6 divided by 2 because each bond would be shared between two atoms. So that gives us minus 3 V of R0. If we have a stronger interaction that affects the second nearest neighbors as well then we need to take account of the potential energy at the second nearest neighbor's distance root 2 over R0 times the number of nearest second nearest neighbors which is 12 in this case divided by 2 because each bond is shared plus the cohesive energy due to the first nearest neighbors. So in this case the cohesive energy of the solid would be minus 3 V of R0 minus 6 V of root 2 over R0. So now we will move on to crystal D phase. First of all we have a frequency which is an atom missing from the latter side as seen in number 1. Next we have an interstitial which is an atom sitting between two latter sides as shown in number 2. Third of all we have a substitutional purity which is a different atom of less than the original atom of the crystal as shown in number 3. And finally we have interstitial in parity which is a different atom sitting between two latter sides. Now you might be wondering what is the importance of all these crystal D phase. But as you can see there is many more ways of arranging an atom silenced crystal. So we are actually in this crystal in presence. And secondly we can use substitutional purity such as number 3 to create a semiconductor that we use on real life today. We hope you found this education informative and we hope that it helps you pass your exams. Good luck.