 Hello. Yes. Yeah. Okay. So the last part we are going to do today is the imperfection of solids imperfection in solids imperfection is nothing but defects. Okay. We also call it as defect. So what is defect or what is imperfection? It is the departure of a crystal which is there in ordered arrangement means when arrangement is different. Okay. For any crystal we have seen the various structures like NaCl and other crystals we have seen the structures. So that is the definite arrangement we have ordered arrangement we have if there is any departure from that particular arrangement or any change in the arrangement of the crystal by any means like suppose if you heat it or suppose if you add an impurities. Okay. So any one of these things will change the property of the solids or crystals. So that change in property that departure from the ordered arrangement is called imperfection or defects in solid. Okay. So right on this imperfection or defect is the imperfection or defect is the departure from is the departure from perfectly ordered arrangement perfectly ordered arrangement of constituent particles of constituent particles in the crystal of constituent particles in the crystal. Next slide down perfect or ideal crystal perfect or ideal crystal exist only at absolute zero temperature that is zero Kelvin ideal crystal exist only at absolute zero temperature or zero Kelvin. Okay. Next line this imperfection can be intrinsic or extrinsic intrinsic or extrinsic extrinsic when we add some impurities into this intrinsic or extrinsic when you add some impurities or in presence of impurities will have extrinsic imperfection impurities. For example, you see if you have gem stones, gem stones are the crystal of Al2O3 is a crystal of Al2O3 and the pure thing is this the perfect crystal that we have ideal crystal that we have it is colorless. Okay. It is colorless in nature. When you add some impurities into this that is extrinsic imperfection. If you add some impurities, you know, in every three plus iron if it is present into this, it's color is blue. Okay, sapphire blue exact color if you see, or if it contains CR3 plus iron with it, it's color is ruby red. This color is because of the change in color is because of the impurities present into this. Okay, so because impurities may be the property of the solid or crystal changes, or it will have a new properties or the color of the crystal changes. Okay, so all these things are, you know, shows the imperfection in solids. Okay, now imperfection we have three types, mainly we have two types, but total different classification of imperfection you see we have three types of imperfection. First one is electronic imperfection electronic imperfection as the name suggests, it is because of the movement of electrons. The second one is atomic imperfection. It is because of the movement of atoms, atoms or ions atomic imperfection or atomic defects. And the third one is line defects. Which we also call it as dislocations or dislocation line defects is nothing much we have a solid crystal and the edge of the site changes, there will be some imperfection into that that we call it as line. Okay, dislocation about a point or along the edge that is line defects or dislocation. Atomic defects or electronic defects like I said, this is because of the movement of electrons, and this is because of the movement of atoms or ions. Okay, this atomic defects further classified into different categories. Okay, we'll write down everything here, but we'll discuss only few things which are important. Okay, we can go through LCRT is given over there, you can just read once not much important these things are what are important things I'll tell you atomic defects. We have three types. The first one is stoichiometric defect. The second one is non stoichiometric and the third one is third one is we have impurity defects. Give me just one second. So impurity defects is stoichiometric defects and non stoichiometric defects. Okay, is stoichiometric defects further it is classified into different different categories. Okay, like the four different types of defects into this non stoichiometric defects are also further classified. Okay, so that's why I'm telling you if you look at all these things. We have a lot of theory to go through it. Okay, so everything is not important, but I would suggest just NCRT you have to read once. I'll just write down all the names here and just tell you the important points, one of the important points that we have here. And few things are important that we'll discuss after this indeed. Okay, stoichiometric defects we have four different types. One is one is vacancy defect vacancy defect. Vacancy defect. Other one is interstitial defect interstitial defect. Next one we have a short key defect, short key defect. And one more we have that is Frankel defect. Both are very much similar, means this two belongs to this two is defined for non ionic solids. The type of imperfection is almost same, but this two is defined for non ionic solids. And this two is defined for ionic solids type is same. But for ionic the name is short key and Frankel. And here it is vacancy and interstitial defects. Okay, ionic solids and non ionic defects. The only difference is here the crystal maintains its neutrality, electrical neutrality maintains over here. Okay, so in all these things, till now you can say 90% of the time they have asked question on Frankel and short key. Now, coming back to non stoichiometric defects. Okay, this also we have two, three types. Okay, like metal excess defect and metal deficiency defect. Two types we have here, non stoichiometric defect. This is metal excess defect, metal deficiency defect, metal excess defect and metal deficiency defect. Okay, now you see at the as the name suggests here, metal excess defect means what we have more metals present metal ions will be more that is metal excess defect. Okay, so metal ions would be more. So how do we get more number of metal ions. Again, we have two, three categories for this. Okay, I mean, we can have metal excess defect in two different ways. One is when we remove some anion from the crystal. Right, initially we have electrical neutrality. So metals, positive ions and negative ions are safe. If you remove the anions will have more number of metal ions present metal ions is cations we're talking about right. So in that way we can achieve this metal excess defect we may have another way is what you add more amount of metal ions on to that. Okay, so the first case by which the metal excess defect possible that is the anion vacancy by the removal of anions. So in this thing, we have two different ways. By anion vacancies by having anion vacancies means what anion you are removing from the site. So eventually what is happening the metal ion is getting more number of metal ions is increasing in the crystal. That's why we have metal excess defect this anion vacancy we call it as f center. Okay, so we call it as f center on this also they have asked few questions. Okay, so one, two, three, these three points are only important. Okay, but yes you have to go through once the NCRT. Okay, so that you will have the idea of what all things. So metal excess defect one possibility is by removing anions another possibility is what by the presence of extra ions means extra cations not ions extra cations. If you add extra metal ions into that in that way also we have metal excess present in the crystal and hence that also leads to metal excess defect. Okay, metal deficiency defect is just opposite of that remove metal ions from the crystal. Right, so few properties of this will tell you impurity defects is what it is the same thing. Suppose we have group 14 element you must have done P type n type semiconductor right. Right, so that is the same thing we have impurity defects is what suppose we have any group 14 elements you add or you mix group 15 elements into group 14. So group 15 plus group 14 gives you what more number of electrons so we have n type semiconductor that is impurity defects. Okay, in group 14 you add group 13 that is P type semiconductor to this kind of thing we have under impurity defects imperfection. We have these three types in this will discuss little bit of electronic defects will discuss Frankel and Schottky. Okay, important point difference into these two and we discussed an ion vacancy. Okay, a few properties will see in metal deficiency defects also. Okay, other things that deficiency part the imperfection part just go through and CRT that will be more than enough. Okay, so first point you write down electronic defects. Like I said, it is due to the irregular arrangement of electron one second it is due to irregular arrangement at zero Kelvin. There's no movement of electrons and hence we say no electronic movement. I'm just giving you the key points here that is it no electronic movement and hence we do not have any conduction no conduction temperature increases as temperature increases transition of electron takes place. Transition of electron takes this basically electrons occupy higher energy state takes place and hence it shows conduction. So when the electron leaves its original site or original position. It creates a whole at its original position right right on due to the movement of electrons due to movement of electrons holds creates and holds are represented by a small achieve holds creates. At the original position of electron where the electron was initially present original position of electrons holds create next concentration of electron the concentration of electron is represented by is represented by a small n and that of hole is represented by a small p. Right concentration of electron is represented by a small n and that of holes is represented by a small p both electron. Both electrons and holes both electrons and holes gives rise to electronic imperfection gives rise to electronic imperfection. Next slide down atomic defects or point defects okay atomic defects or point defects are the same thing. This type of defects observed due to movement of constituent particles due to movement of constituent particles previously it was electrons here we have particles to possibility we have when the particles are missing from its from its original position. In the lattice right it is missing from the lattice completely another one that it occupies the industrial sites on the same lattice okay leaves its original position and occupies the industrial sites. Okay both way this kind of defects possible okay like I said the point defects. Are again classified into three categories that is the stoichiometry defects and then we have non stoichiometry defects and then we have impurity defects so in stoichiometry defects we have first one we are going to see that is short key defects short key. Write down write down it generally observes in AB type crystal it generally observes in AB type crystal it generally observes in AB type of crystal. A plus B minus I nick AB type of crystals and in this type equal number of cations and anions equal number of cations and anions are missing from their are missing from their original. Original or normal lattice sites original sites so when they're missing when they're missing from their original position it creates holes right. It is observed in a strong ionic compounds like NSCN KCN KBR CSCN AGBR AGBR also shows us. Okay few properties of this kind of defect you must remember like the ions are missing from their original sites hence we can say density of the crystal decreases in this type right stability also decreases lattice energy also decreases lattice energy and stability both decreases. And property because the disorder disorderness is increasing it was originally it was ordered arrangement defects is all about you know the disorder arrangement right or the other disorderness so we can say that and property because the defect increases so property based question they have asked in this okay short key defect. Examples and property based question. Okay, now the second one is. Did you copy this second one is frontal defect this type of defects observes when the ions in bracket you write down usually cations because of the ions usually cations. Of the lattice of the lattice occupy the interstitial interstitial sites leaving a corresponding number of normal site vacant means polls created repeating this. Yeah, this kind of defects observes when some of the ions usually cations some of the ions usually cations of the lattice occupy interstitial sites interstitial sites. Leaving a corresponding number of holes. Next slide. It creates vacancy defect it create vacancy defect at original site because you know the position is getting vacant right so vacancy defect at original sites and interstitial defects at the new site. New site means where the ions goes the new site where the ions are present. There we have interstitial defects interstitial defects and vacant defects at the original sites. There are few we have one condition one or two condition for this but obviously we have some exceptions also here. That's why I said you have to know memorize this. For all those crystals whose coordination number is low coordination number is low can show this kind of defect. Okay condition size difference. Of an ion and cation is more right so size of an ion. Is bigger than or the size of an ion should be bigger more than that of cat ion. So in this case these two cases this kind of defect possible see alkali metal highlights the size of cat ion and an ion are very much similar like the difference is not that great. Hence alkali metal highlights does not show this kind of defect. Okay right down this point the size difference in alkali metal highlights is not high or more. Hence Frankl defect is not observed. See the ions does not leave the site okay means leave the crystal it is present in the crystal only but not at its original position. Okay if you have NCRT you can open it and you can see the diagram okay or after the class you can see right so ions are present in the crystal but not at its original site. So because of this only the density change is not there no change in density no change in density. Here also lattice energy and stability decreases decreases disorderness increases so entropy also increases the molecule which shows this kind of defect is AGCL. AGPR again I am writing it down here it is important it shows both defects AGPR, AGI, ZNS all these shows triangle defect. So in AGPR both Schroedtke and Frankl defect observed since AGPR is ionic but again the size difference is also very much. That's why Frankl it shows yes now we'll see one or two things in non stoichiometric defects, non stoichiometric defects. This kind of defect observes in non stoichiometric crystals mainly this observes in non stoichiometric crystals. This also classified into various categories like I said we have metal excess defect. So metal excess defect is possible in two different way one is you add the metal ions in the crystal will have excess of metal metal excess defect. Other one remove an ion from the crystal that is an ionic vacancy right now in this type metal ions or in this type metal ions or cations metal ions or cations are in excess in excess. This defect may develop in two ways this defect may develop in two ways the first one is in two ways. The first one is when excess cation excess cation occupy occupy the interstitial position so number of cations increases metal excess defect and the second one is we call it as an ion vacancies and vacancies. Write down in this write down when a negative ion negative ion is missing from its lattice sites when a negative ion is missing from its lattice sites leaving behind leaving behind a vacancy or a hole leaving behind a vacancy or a hole. Which is occupied by which is occupied by by the electrons which is occupied by the electrons in order to maintain in order to maintain electrical neutrality to maintain electrical neutrality. Trapped electrons are called f-centers the trapped electron are called f-centers centers f-centers which is responsible for which is responsible for imparting color to the crystals which is responsible for imparting color to the crystal. Which is responsible for imparting color to the crystal this defect is similar to short key defect similar to the short key defect and it is observed in the crystal which shows short key defect. So this is f-center just one thing you have to take care of write down one note greater the number of f-center more will be the intensity of color greater the number of f-center more will be the impurities sorry the intensity of color. Okay, so this is it for imperfection these two things no they have asked in the exams okay but ncrt like I said you must go through it is completely theoretical you have to memorize certain things okay and that is it the first part you can understand everything logically all the positions of point and everything. But this thing you have to memorize another thing is what there is one more thing that is magnetic property that is paramagnetic behavior paramagnetic diamagnetic behavior we have ferromagnetic substance anti ferromagnetic substance also there for that it's not at all important but for that I will share one pdf okay so whenever you get time you just go through that pdf it is more than enough given into that. Fine, so this is it for this chapter okay we are going to start next that is chemical kinetics. Okay, just one minute.