 Next you write down imperfection in solids. What is imperfection or defect? Exactly changes. See imperfection or defect is the change in the arrangement of atoms. Not only arrangement of atoms, we can also change the properties of the atoms. When you heat this or when you mix some impurity into it, then the property changes from order arrangement to disorder arrangement. This deflection from the order arrangement, whether in terms of properties or color or anything you can say, this deflection is nothing but the defects or imperfections. Improfections possible when you heat the compound, heat kia, electron kia, heat gain kia and it jumps to the higher energy level. And because of that we have current changes also. So, imperfection right on the heading, imperfection in solids, imperfection is nothing but the deflection from perfectly ordered arrangement. Deflection from perfectly ordered arrangement of constituent particles in the crystal. Right on the next line, perfect or ideal crystals can only exist at absolute zero temperature or zero calorie. Perfect or ideal crystal can only exist at absolute zero temperature. These defects may also change the properties of the solid. Like you see one example, gemstones are the crystal of Al2O3. So, Al2O3 and it is colorless. Now, when you add some impurities into it, suppose Fe3 plus iron you have added into this, then the current changes to blue. If you add Fe3 plus into this, the color changes to red, ruby red also. So, these are the impurities. When you add those impurities into these gemstones, the color changes. So, this is what the ordered deflection in the property we have. Or perfectly ordered arrangement if you are changing the position of atoms of the constituent particles, then that deflection is nothing but imperfection in solid. Imperfection is possible because of impurities or at high temperature when you heat this. Two types of imperfection we have. Two types of imperfection, write down the first one, electronic imperfection. Electronic imperfection as the name suggests, it happens because of electrons. Electronic imperfections. Semiconducted we have done in physics, p-type and type, doping, semi-conductor. Electronic imperfection. It is because of irregular arrangement of electrons. Electronic means electrons, irregular arrangement of electrons. As the temperature increases, some of the electrons occupy, the higher energy level and shows conduction. So, when the electron leaves its original site, suppose the electron is present here. Now, when you heat this or when you provide at high temperature, this electron jumps to the higher energy level. So, we will have a hole over here at the original site of the electron. This hole creates by the movement of electron from one position to another position. The concentration of electron, write down, the concentration of electron is represented by small n. Hole is h, we represent the hole as h and the concentration of holes is represented by p. Because of this transition only, the electron or the solids, whatever solids we have, that show conduction. Conductive nature is because of these electrons only or this property only. Conductive nature is because of this. Both electrons and holes give rise to the conductive nature of the crystal. Because of both of this only, the crystal shows conduction. So, it is electronic imperfection is what by the movement of electrons at higher temperature. Generally at absolute zero temperature or zero Kelvin, electrons are, there is no movement of electrons. And we can say there is no mobile electron present and no conduction is there. No mobile electrons and no conduction. When you increase the temperature, the electron occupies higher energy level, becomes mobile, creates hole and both this mobile electron and holes give rise to the conduction in the solids. Next, write down atomic imperfection. Atomic imperfection, we also call it as point defect. Atomic imperfection or point defect. Write down this type of defect is observed because of the movement of constituent particles. This can take place in two different way. When the first one, when the constituent particles are missing from constituent particles are missing from their original sides and the second possibility is when the constituent particles are missing from their original sides and occupy and occupy, occupy interstitial vacant sides or the position of other particles. Any vacant side it occupies or the position of any other particles. Now this defect also, let me write down atomic defect also classified into three categories. All these are not important, we will see just two way to go. Three categories, the first one we write down, defects in stoichiometric crystal. Second one, defects in non stoichiometric crystal. Third one, line defect or dislocation defect. Defect in stoichiometric crystal, defect in non stoichiometric crystal, line defect or dislocation defect. These are the three different atomic defect we have. In this the most important one is defects in stoichiometric crystal. You must have heard about Schottky defect and Frankl defect. Schottky defect and Frankl defect are observed in stoichiometric crystal. So write down the heading, defect in stoichiometric crystal. Like I said, when the original position of the atoms are missing, suppose A B atoms are arranged like this. A cation and B anion, two types of defect, Frankl and Schottky. So these are the position which is given to the various cations or anions here. A plus and B minus. Now if one of the cations or anions are missing from its original site, suppose A plus or B minus is here. A plus and B minus is missing from the original sites. So this earlier it was an order arrangement. When these two atoms are missing, ions are missing from their original site. Now this becomes the defect, the crystal is defect. It is imperfection that missing of these ions are imperfection of solids. So this missing, where the equal number of cations and anions because the crystal as a whole should be neutral. So it is not like one A plus is missing and B minus is present. Electrical neutrality must be there. So this kind of imperfection is there. This imperfection we called as Schottky defect. S, C, H don't write this as Schottky defect. Equal number of cations and anions are missing from their original sites. Now it is also possible that A minus B minus is present here and A minus leaves its original sites and occupies any interstitial site like this. So this defect overall it is also electrical neutral. So when the ions occupies interstitial sites or the sites which is meant to be for any other ions or atoms of the crystal. This site occupies the crystal or ions position occupies the crystal. That question should not be meant for that particular ion. So this kind of defect we call it as Frankel defect. Based on definition only we ask questions on this. Some properties also we have like suppose if I talk about the density in the Schottky defect. Density can be overcome because ions are missing from the original sites. So mass decrease or density decrease. In this case density won't change. Mass is there. Like this we have certain properties of Schottky and Frankel defect. First of all these two defects are present in the Schottky defect. First defect right on Schottky defect. Just two three points you will see. In this defect equal number of cations and anions in this defect equal number of cations and anions are missing from their original sites. Equal number of holes creates. It is observed in ionic compounds. As a question are that in which of these compounds Frankel defect observed. Schottky defect observed. Ionic compound of AB type. For example NACL, KCL, KBR, AGBR, CSCL etc. Density decreases. Density decreases. Lattice energy and stability also decreases. What about entropy? Entropy increases. Entropy increases because disorderness is increasing. Entropy increases in both cases. Frankel and Schottky. These are the two three points we have in Schottky defect. Next write down Frankel defect. Frankel defect. This defect is observed when an ion in bracket you write down usually cation. Usually cation changes its position because cations are smaller in size. When an ion usually cations of the crystal occupy any interstitial sites leaving a corresponding number of holes at the original site. Next one. It is not observed in alkali metal halide. Alkali metal halide may Frankel defect is not possible because size of cations and ions the difference is not that much. Alkali metal halide may the difference is not that much. Size difference and that is why Frankel defect is not observed. Example write down AGCL, AGBR, ZNS, AGI etc. AGBR you take care of in this both kind of defect is possible. Schottky and Frankel. Last one maybe we have done this example. AGBR may Schottky defect also possible. And this question they have asked once. You must keep that in mind that in AGBR both Schottky and Frankel defect possible. There is no change in density. Lattice energy stability decreases and property increases. After this we have defects in non stoichiometric crystal. It is not that important. Hence the RT it is given you can go through. Non stoichiometric crystal may we have again two types of defect. I will just tell you here. One is metal excess defect. Metal excess and other one is metal deficiency defect. As the name suggests metal excess defect is what? When the number of metal ions is more. Number of metal ions is more you can achieve this in two different way. You have to metal ion to add here right. By the addition of metal ion or you remove an ions. Removal of an ions. Then also the metal excess will be there right. Metal deficiency is what? You add an ion into this or remove metal ions. In both way the defect is possible. There is one term into this. Write down that F centres as definition. You write down F centre. Capital F centre. Write down when a negative charged ion. When a negative charged ion is missing from its original site. It creates a hole. It creates a hole. And to maintain electrical neutrality. This hole is occupied by. This hole is occupied by the electrons. This hole is occupied by the electrons. They explain when the electrons are trapped. In an ion vacancy. When the electrons are trapped. In an ion vacancy. Then it is known as F centre. So basically from the another layer. The electron diffuse into the vacant site. From which the an ion has been removed. So when the electrons occupy that an ion vacancy. Suppose this cation is not present in the site. When the cation leaves its original position. This vacancy we call it as cation vacancy. Since cation is coming out from there. When an ion comes out it is an ion vacancy. So when the an ion vacancy is occupied by an electron. Then this is known as F centre of that. That is what the definition. Once they have asked question on to this F centre. When an ion vacancy leaves its original side. It becomes the F centre. One just last line into this. Greater the number of F centre. More will be. Greater the number of F centre. More will be the intensity of colour. Because more will be the electron transition. That is why the intensity increases. So these are the defect we have done. Defects with electromagnetic crystal. Next we have to do this electrical and magnetic properties. Electrical properties we have already done. This is P type and N type semiconductor. We have to learn I am not doing it right. Magnetic properties there are 5-6 different types of compounds. We have ferromagnetic, ferrimagnetic, paramagnetic, diamagnetic. Examples and all we will see. And the last part of this chapter is that Bragg's law. Bragg's law we will discuss and then we will see some questions. Ok.