 Lot of information you cannot get like why a specific compound is colored right what happened to their magnetic properties because these are the things we are really really interested in. So, this is where crystal field theory comes in of course, it is based on the failures of the balance bond theory or as that is how in the book you read that where balance bond theory kind of fails cannot explain further and crystal field theory basically picks up. So, of course, we can just learn crystal field theory, but the problem is balance beam theory is so simple I think nobody kind of see you cannot forget the history of something and just take the present I mean present is something different not crystal field it is something different right which we may not be or we will not be talking too much. So, it is you know present means temporarily present 100 years down the line it would be explained in a completely different way or more better way of course, crystal field theory has tremendous limitation as well, but we may not be talking about those. So, as we progress or as the chemistry understanding progress we will try to do. So, what we are saying that balance bond theory really cannot explain tetrahedral and square planar ok when it is any distortion what balance bond theory is discussing is an ideal situation kind of any anything bond elongation shortening these things cannot be explained by balance bond in a moment you will see how the distortion is going on by crystal field theory. Color of complexes of course, you cannot have any idea about the color what color the complex should be I say compound is this hybridization or this many ligands are there this there that there crystal field theory can explain. However, we did not explain yet, but balance bond theory cannot explain those. Temperature dependence why magnetic properties are dependent on temperature if you increase the temperature what happens whether magnetic susceptibility or the magnetic behavior goes up or goes down or how it goes down or how goes up those sort of thing will be discussing ok. Now, crystal field theory first we have to look at the orbital this is something you have to kind of have it within your mind very clear what we are talking about the atomic orbital these orbitals mainly the 5 D orbitals right we have 5 D orbitals how they are and along the axis how they are where they are. Now, this is the z axis or g axis whatever you want to call ok. Now, the dg 2 orbital is going to be like this the electron density is going to be over here and over there along the z axis. So, axis you can think along this one let us say this is x axis this is y axis this is z axis ok in 3 dimensional scenario you can take this corner any corner one axis another axis nice laser point a failing any corner you can pick up x y z of course, 90 degree angle it may not be always true here. Now, this is d z 2 orbital so, along the z axis this is dx 2 y 2 along the x and y axis and this is let us say dy z that means, in between y and z. So, if you look at here if this is z axis this is the electron density over here and the lobes are here and below this one there is lobe ok. If it is x and y axis then dx 2 y 2 will be along these x and y axis along just right on top of those axis right on top of the z axis is d z 2 right on top of x and y both plus and minus reaction is going to be your dx 2 y 2. And dx y will be in between dx y where is dx y dx y see this is let us say x axis or whatever y axis x and y as you see these are right on top of the axis in between x and y axis is dx y. Similarly, in between y and z is going to be dy z. So, this is z axis centre the lobes are here this is dz. Now, if you look and say that this is let us say x and this is y dx 2 y 2 is going to be here right. So, and dx y is going to be. So, this is y axis this is x axis right on top of y axis sorry we will come to that. So, it is going to be like that ok. Now, you have to I am sure you have seen it before you have to be really really clear about the they are positioning I think we will come to that let me tell show you where they are over here no we will come back in a moment let me tell you. So, what crystal field theory assumptions are it is very simply these are electrostatic interaction it is a metal centre is a cation ligand is an anion most often. So, it is a cation anion interaction or electrostatic interaction ion ion interaction or ion dipole interaction previously we are thinking just about the covalent interaction right. Now, if you are thinking so, metal about metal metal has electrons if you are bringing ligand ligand has electrons. So, these ligand and electrons and metal electrons are going to repeal each other they are going to they are electrons same charge right although metal is positive ligand is negative let us say or neutral whatever it is, but if you bring them together those electrons of the ligand and electrons of the metal they are going to repeal each other. So, thereby the energy of the total system going to be increased if D level energies are for example, over here if you bring the ligand from the equal distance or from the all distance or all direction equally then then also the energy of the D orbitals will go up it is a spherical let us say cricket ball you are going to put the pressure on cricket ball from all directions cricket ball is going to be destabilized or in this case ligand approaching ligand is going to make cricket ball destabilized ok. Now, this is under ideal situation where all the ligands let us say are coming from every distances or every directions all the distance all the directions. Now, in reality what you have seen is ligands are not there from every directions it is specific ligand is here, here, here, here, here and here only few directions this is the direction for z axis let us say this is the z axis this is the let us say whatever y axis this is x axis right. So, ligands are going to approach the metal center only from a specific direction not from here it is just along this direction not from here not from here not from there it is a specific the direction. Now, these are the directions where the metal orbitals are there you have d z 2 there you have d x y this is the one where you have d x y. So, eventually what you will see is I will show you since ligands are coming from this direction directly those orbital d z 2 and d x 2 y 2 orbitals are going to be rippled very much means they are going to be unstable they are going to be high in energy. So, over here 5 d orbitals are there since ligands are coming specifically from z or towards z axis y and x axis any orbital that is facing those axis directly they are going to find the consequences that means, they are going to have the energy increased their energy will be increased. Any other orbital for example, d x y which is over here in the middle in the middle they are going to be perturbed, but not too much in reality with respect to this one they are going to be stabilized because this is the total stabilization with respect to that something is going to be destabilized something is going to be stabilized ok. Now, let us look back all the orbital if you look back one more time very carefully this is the g z 2 anyone has anything to say please speak out. Now, d z 2 orbital d x 2 y 2 orbital and you can see all these orbital right now also if it is not clear you look back at the note I am sure it will be very very clear the pictures are very clean. Now, as we are saying that plus and minus attraction electrostatic attraction will be there. Now, 2 of these orbital which is d x 2 y 2 and d g 2 or d z 2 these are the orbital let us say all these orbitals are there these are the ones which will be facing the ligand directly like this. So, ligands will be coming directly from 2 different angle or from 2 different direction for d z 2. So, d z square orbital will be high in energy right it is it was previously it was all of them are same having same energy or so called degeneracy 5 d orbital where degenerates that is so far you have mostly learned of course, you may have learned this one as well, but since you see that there is a discrimination there is a preferential attack you are going to get it destabilized because they are going to interact directly. Now, if you look at the d x 2 y 2 this is the d x 2 y 2 orbital and 4 of the ligands are coming from these direction exactly of course, this is going to be also destabilized. So, what you have learned so far is d z d g 2 and d x 2 y 2 are going to be destabilized, but if you are looking at let us say this is d x z orbital x axis and z axis d x z orbital and the ligands are approaching right actually from the middle not directly towards these lobes. So, their energy will not be overall destabilized because we have already destabilized by bringing the ligand comparatively they are going to be stabilized that is how the ligands are coming right sorry that is how they are coming in. So, they are not fitting the bill right on top of each other they are just you know squeezing in not head on collision. Now, so d x z will be stabilized d x y d y z is the same scenario it is just different axis. So, overall we see that it is split into like this two of them getting destabilized three of them getting stabilized. Stabilized means stabilized with respect to where it started not in the free ion over here this is a free metal ion with respect to free metal ion when you have a metal complex formation it is all the d orbitals are going to be net destabilization will be there their energy is going to be high with respect to this some of them will be destabilized some of them will be stabilized, but the net destabilization is going to be this much. If you have a free metal ion it is stable the moment you put ligand in it it is going to be unstable or destabilized with respect to that destabilization ok. So, that is how it is going to be, but with respect to free metal ion of course, they are destabilized ok. Now, this is what is octahedral field is all about you see octahedral complex 6 ligands are there surrounding the metal center 5 d orbitals getting destabilized and further splitted this is no longer degenerate of the same energy right. Now, this is also another way to look at it 2 ligands and these black balls are ligands and how they are coming and all the d orbitals are super imposed over here you can see which are facing what ok. Now, this is for octahedral field this is called E g orbital E g orbital and this is T 2 g orbital 3 of them. So, E g is d x 2 y 2 d z 2 and T 2 g is d y z d x z d x y ok. So, 3 of them and 2 of them. Now, the extent to which with respect this is called bary center where the 0 is ok. With respect to that the destabilization will be the same amount compared to the stabilization why it seems like unsymmetrical because there are 3 orbitals. So, 6 electrons can be filled 6 electron versus 4 electrons. So, 4 time destabilization and 6 time stabilization. So, it is a there is a factor this distance from the bary center this distance is 0.6 this is 0.4 from the middle this is 0.6 and 0.4. So, from here this is going to be 0.6 this is going to be 0.4 ok I should have stabilized I should have switch off this one 0.6 0.4 ok we will come to that again. Now, some more information are given which you can read very clearly I will not dwell too much on that stabilized one destabilized one this is also another way of looking at this the same thing exactly same thing you may not be able to see it clearly from here, but in slide it will be clear d z 2 d x 2 y 2 and the 3 2 orbitals and 3 different orbitals in the compound form or in how they interact ok. Further it is much better I think this is the last slide hopefully on that you see z d z square and d x 2 y 2 d z x d y z d x y same thing how the ligand is coming. See when you take the print out of these things if you take the same print out I do not mind, but the information is not different, but once you are seeing in the computer for example, you will be able to see it clearly what exactly we try to say that will give you a crystal clear picture hopefully what is going on in here. So, once again I will take the break in a moment this is the 3 5 of the total distance is called delta 0 or 10 d q this is going to be your 6 d q this is 4 d q or so to speak 3 5 delta 0 2 5 delta 0 this is something you need to remember the total is called 10 d q 4 d q and 6 d q 0.4 and 0.6 4 d q 6 d q ok. If it is delta 0 you are saying this is going to be 0.4 delta 0 this is going to be 0.6 delta 0 and these are the easy t 2 g we will be coiling the difference between them is delta 0 10 d q show on so forth anyway. So, let us continue over here what we see this is the total 10 d q we are saying what is d q it will be clear soon enough or this is the delta 0 the distance between this t 2 g and easy or the energy difference between these 2 some of them are destabilized some of them are stabilized let us say let us take some little bit more practical example you have a titanium hexa aqua complex with 3 plus Scandinium titanium Scandinium titanium ok. It is d 2 s 2 it is going to be d 1 then after 3 plus so 3 d 1. So, that means, no longer we will be saying it 3 d 1 we are going to say it t 2 g 1 easy 0 because if you see the filling up of the electron now it is going to happen the one which is stabilized first and then either over here or back to here. So, the filling of electrons we are trying to see no longer we will be calling it d 1 it has to be defined at as t 2 g what easy what let us say t 2 g 5 easy 0 t 2 g 3 easy 2 t 2 g 4 easy 2 or t 2 g 6. So, how we are going to do that this is what we are going to discuss. So, in other words whether all the let us say you have 6 electrons 6 electrons if you are having each of them are one orbital therefore, technically you can have 6 of them over here or 3 of them over here 2 of them over here and another over here 4 plus 2 you can say g 6 plus 0 or whatever other power mutation combination you want to have what order these d orbitals will be filled that is what we are going to discuss. The answer to that question is very simply it will depend on the ligand that is why it is also called ligand field stabilizes an energy ligand if it is a strong ligand what is a strong ligand let us say I will come back to that again if it is a let us say cyanide cyanide is a strong ligand ok aqua water water let us say for example, usually a weaker ligand or it is all relative again there is a spectrochemical series you will bring ok that will tell what is strong ligand what is weak ligand fluoride may be a weak ligand ok. So, chloride may be weak ligand CO may be a strong ligand ok so on. So, depending on the difference this energy is having like how much difference is there between T 2 g and E g it is this much or that much if it is this much difference then electrons will be occupied all T 2 g and E g because you know that Hunz maximum principle that spin has to be maximum and so on. But if it is this one that Hunz rule may not be applicable here because you know it is very big. So, putting electron in this orbital E g orbital is going to cost you too much of energy of course, another problem is the pairing for if you want to pair up pairing energy is also there. If you want to pair up over here some energy you have to give whether pairing energy is high or the distance or the energy difference between this T 2 g is high that you need to kind of know you know you do not need to memorize we are going to tell you what is the scenario ok. So, we need to know what is the ligand what usually is the pairing energy what is the oxidation state of the metal that also varies higher the oxidation state you will see the splitting will be high this T 2 g E g gap will be high 3 d to 5 d gap will be increasing 2 plus 2 5 plus gap will be increasing. Therefore, if the gap is increasing pairing become easy because you know it cannot go too much if it is gap is too much. If gap is low then pairing will not occur it will be both in T 2 g and E g if this is E g this is T 2 g ok that is what we are going to see now. I am kind of summarized over here it is going to be T 2 g 1 E g 0 now everything you have to explain or you have to write in this format why we see purple color in this titanium hexa aqua complex why do we see purple color it is like this the UVB is maximum the absorption is going to be this 2300 or 2 2 0 3 0 0 wave number. So, that is actually the gap between the T 2 g and E g we will show. So, let us say this is this is your T 2 g electron and you put the energy the light it is going to convert from T 2 g level to E g level and that is where you see the in terms it comes out the absorption energy where it absorbs that means, how much energy you have given to bring let us say T 2 g electron 1 electron from here to here that is what nothing, but you see as absorption the peak you see or you have a metal complex you shine light you want to see the electronic transition from one level to other. It could be let us say sometime T 2 g T 2 T 2 g or it could be usually the for one to see you have to have T 2 g to E g conversion from T 2 g orbital any of them because they are degenerate to over here that is the energy you need and that is is going to be your absorption energy and depending on that how much energy you absorb as we say why the color different color comes how much energy is required based on that or what wave number is required based on that you will be able to see the color. So, you give them white light simple light we end up seeing some color based on what is being absorbed and what is being emitted or indirectly what is being emitted. So, for T 2 this titanium hexa aqua complex we see that this is the UVVs absorption this is nothing, but this transition from T 2 g to E g level and that is how the peak is coming ok that is the absorption that is happening from for transferring T 2 g electron to E g electron. Of course, there could be multiple transition there could be multiple if it is a simple electron system one electron system if you have two electron systems three electron four electron five electron and so on and based on the electronic configuration you can have multiple transition. Therefore, your peak could be like three four peaks or I mean your spectrum could be having three four peaks or different region different things can happen. So, simply speaking some sort of transition has to occur in the orbital itself five of them are degenerate you are not going to explain that is why you cannot explain color by crystal by valence bond theory, but crystal field theory gives you an idea of where the origin of the color is this is nothing, but transition of one sub level to another one right. So, this is where crystal field theory becomes superior compared to your valence bond theory. Valence bond theory what you have done d 2 sp3 or sp3 d 2 whatever sp3 and so on there you cannot explain where the color is coming from ok enough. Now of course, as I said there are scenario where you can have more than one electrons right. So, d 1 to d 3 so of course, wounds rule will be promoted. Now, for 4 electrons you can have d 2 g 4 easy 0 d 2 g can have total up to 6 electron or you can have d 2 g 3 easy 1 3 of them are going to be filled out after filling out the fourth one will be the easy 1 easy right. Now, I will come to come with that more pictorial diagram I think I will skip that now this is what it is. So, d 2 g orbital 1 electron d 2 g orbital 2 electrons d 2 g orbital 3 electron there is no story of easy because easy is high in energy why it will go to high in energy. After d 3 then you have dilemma then you have problem whether you send it to easy or you pair it up with d 2 g. So, there are two scenarios high spin complex will have d 2 g 3 easy 1 d 4 option 1 option 2 will be d 2 g 4 easy 0 this is d 2 g this is easy easy over here nothing in there. So, you have low spin complex this is high spin complex because four unpaired spins are there here you have two unpaired spin. So, up to d 1 d 2 d 3 you do not have to worry at all you just put d 2 g 1 d 2 g 2 d 2 g 3 after that whether it is d 2 g 4 easy 0 d 2 g 4 easy 0 or d 2 g 3 easy 1 which one is going to be predominant or which was going to be happening that will be determined by ligand metal which metal it is what the orbital they are having what is their oxidation state. All these factor will put together will determine whether it is going to be a high spin complex or low spin complex. It is not complicated at all just go through simply I will I will try to explain when what you can expect you do not have to remember again you do not have to remember what will be the delta 0 and what then what will happen that that sort of memorization is not required ok. So, in other word if delta 0 or that 10 d q value we were talking difference between t 2 g and easy. If this is small then you will see t 2 g 3 easy if that difference is small the spin will try to be maximum or you know electronic spin will be maximum. So, t 2 g 3 easy 1 will be happening if delta 0 is small for this to happen t 2 g 4 to happen you have to pair this 2 electrons right. That means, you are dealing with pairing energy. If pairing energy is favored if pairing energy is less compared to this delta 0 then you are going to have this low spin configuration ok. Now of course, lot of things I have given written the same thing again and again written, but essentially once it is clear to you you do not have to read this slide too much ok. I think we have explained already. Now, I will just give you a phenomenon. So, what we again what we have said up to d 3 you do not have to worry it is going to be t 2 g 1 t 2 g 2 t 2 g 3 after d 4 you have to decide that again let us say at d 8 you do not have to worry it is going to be t 2 g 6 easy 2 1 2 3 4 5 6 7 8 whatever way you want to fill out d 8 d 9 d 10 you do not have to worry it is going to be only one configuration possible because your goal is to minimize the energy without compromising the spin of course, one's rule says the spin should be maximum right. You try to do that, but while you are trying to do that you have to also mind the gap distance between t 2 g easy whether it is going to be unpaired spin or paired spin. After filling t 2 g you have to up from 4 5 6 really the 1 cases where and 7 as well 4 5 6 7 you have to worry about whether it is going to be high spin or low spin. Up to 3 it is going to be always high spin there is no low spin scenario almost and after 8 8 9 10 it is always one configuration 4 5 6 7 it is going to be high spin or low spin that is what you are going to high spin means spin is maximum low spin is spin is minimized with the given situation. Now, something like these complexes if you see some easy complex like very soothing for the eyes those are going to be high spin like iron aqua very easy complex looks like water molecule iron is there 3 2 plus 2 plus mind you easy complex the difficult complex could be 3 plus means which is more higher charge. Now, this is going to be high spin over here because the delta 0 you see is this much pairing energy is high pairing energy high means you are not going to get it paired you are going to have the unpaired spin right. Now, iron hexa cyanide we are all talking about octahedral complex do not forget that 6 ligands are there we we did not talk about tetrahedral as of yet. So, 6 of them this is going to be a strong ligand cyan cyanide is a strong ligand that means the gap between T 2 G and E G is very high this will be D 6 right. So, those 6 electrons will be T 2 G 6 not T 2 G 4 E G 2 I think some of them are some of you are having little bit dizziness let us see try to explain in the board what we are having let us say D 6 this is T 2 G 3 of T 2 G and 2 of E G you can have this as one scenario right other scenario is nothing here all paired up right. So, this is T 2 G 4 E G 2 this is a high spin situation that is what is happening in iron hexa aqua complex 2 plus. Now, iron cyanide 6 FECN 6 hexa cyanide 4 minus now you have D 6 total electron right. Now of course, how it is it is iron 2 plus this is also iron 2 plus both of them are iron 2 plus iron 2 plus that is why it is 2 plus iron 2 plus 6 minus that is why it is 4 minus outside right or both of them are D 6 electronic configuration only thing that is differing is the ligand metal is in the same oxidation state hexa coordinated ligands are different. What you are seeing here is the distribution of electrons are different the first one will have this electronic distribution second one is going to have this electronic distribution because let us say. So, to speak the difference between these two guys is high distance this difference is very large if you look at this delta 0 or 10 D Q is this much pairing energy is less. So, thereby it will pair up very easily it will electron cannot go and jump over there in this case the pairing energy is high, but delta 0 is small. So, it is going to be it is going to follow your Hund's rule or I mean of course, it is always following Hund's rule sometime there is no option when there is no option you are going to end up getting that configuration. This is usually speaking most of the cases I think high spin will be preferred of course, most of the cases is a wrong statement, but it is a ligand dependent metal dependent, but lot of things that we see in you know in the regular books usual books those are going to be high spin species unless it is high oxidation state of the metal and strong ligand it is not going to be low spin. If it is high oxidation state let us say iron 4 plus or you know some high oxidation state and ligand is strong ligand then you are going to see low spin because the T2G and easy splitting is going to be high ok. Now, next one cobalt F6 cobalt is here 3 plus 6 of the fluoride 3 minus total D7 configuration cobalt is D7 S2 iron cobalt here and then if it is iron cobalt nickel D7 S2 it is 3 plus right I think something is wrong there is it not it should be D6 right. Let us assume that this is D7, but this charge are wrong cobalt cobalt is D7 S2. So, 9 electrons if 3 are taken so 2 are taken then it is let us say this is going to be your 4 minus the charge is wrong here I do not know how come. So, anyway it is a D7 system both of them are D7 system ignore the charge just take my word ignore the charge D7 system D7 system one is high spin another is low spin. It is also to tell you sometime you see the ammonia complex is going to be low spin sometime it is high spin again that depends on the metal center I will give you a summary. Let me give you the summary the delta 0 will be increasing in the short 3 D, 4 D, 5 D, 5 D will be high higher oxidation state will give you the higher delta 0. Now, over here you see with the chromium chloride aqua ammonium cyanide the energy between t2g and eg how they are differing. So, you can say that this is a weaker ligand this is little bit stronger this is more stronger this is the strongest in this series. So, the difference between t2g and eg can tell you what is the strength of these ligands are. Depending keeping the metal constant oxidation state constant you are changing ligand and you are saying that the splitting you are varying. So, that will indirectly measure the strength of the ligand ok. Now, over here you are keeping ligand constant oxidation state constant everything constant, but you are changing the metal center cobalt rhodium radium in the periodic table look at. Now, you see how they are increasing. So, the overall trend is 3 D splitting with the least then 4 D then 5 D metal oxidation state will also vary that is also over here all these things summarized together I will tell you what is summarized to this is what it summarized to ok. You can take a series of compound just vary one thing either ligand you vary or metal you vary you keep on doing you come to a conclusion that 5 D will have higher splitting then 4 D and 3 D and higher oxidation state will have higher splitting. Now, there is something called electrochemical series this is what is electrochemical series. This is the strongest ligand then this one then that that that so. So, the idea here is if you have a high oxidation state and strong ligand you are definitely going to get a low spin complex high oxidation state splitting will be high strong ligand splitting will be high. So, low spin complex means it is the splitting is going to be high. So, the electron cannot jump to the E g. So, it is going to be low spin spin will be minimized it will stay in T 2 G. Now, you can think about the different permutation combination that is why it is not that very easy to say what is going to happen unless you give the exact combination. So, the strong field ligand they will tend to give you high delta G or delta 0 right T 2 G E G separation will be high therefore, it will give you a low spin complex. Strong field ligand will tend to give you a low spin complex, but that does not mean that any metal you take you will always get low spin with let us say cyan or you know this any of the alkyl or nitrite. You have to of course, you have to you also have learned that 5 D will have more splitting than 4 D and 3 D higher oxidation state will have more splitting than lower oxidation state. So, it is a combination of all these 3 factors where the ligand is in terms of spectro electro chemical or spectrochemical series not spectral spectrochemical series where the ligand is whether it is strong field this is the strong field these are the weak field where it is and then what is the oxidation state of the metal and what orbital metal is having ok. If everything strong strong strong then you are going to get high splitting low spin if it is very small you are invariably going to get high spin ok. You just read through little bit first the slide look at the slide and then go through the books I hope it will be clear ok. Now, it is summarized in here once again and this is the summarized for this ligand. So, overall after having this you should be able to calculate the crystal field stabilization energy how much with respect to the 0 how much stabilize or destabilize it is. So, over here each of the electron over here I said it is 4 d q right 4 d q and this is 6 d q. So, you can see that 3 of them let us say if you have 3 of them 4 this is 4 d q 4 times 3 will be 12 and 2 times 6 will be this is 6 d q this is also 12. So, 3 over here 2 over here net stabilization will be 0 nothing is left 3 over here 2 over here symmetrically field 4 times 3 2 times 6. Now, the moment you put it here one electron the stabilization energy crystal field stabilization energy that is what called crystal field stabilization energy 3 and 2 is 0 in this case it will be 4 d q. Of course, d q has a value different for different compound as we have seen in that d q is changing, but we do not you know memorize those data just say that it is 4 d q. 4 d q could be 500 wave number 4 d q could be 2000 wave number, but this is 4 d q that d q depends on what is the extent of splitting how much how far it is splitted ok. Now, this is having 4 d q stabilization this configuration 3 and 2 cancels out just 4 d q left. If you have one more electron over here 3 2 cancel out 8 d q right 1 more 12 d q 3. So, you can calculate also 4 times 6 is going to be 24 and 2 times 6 this is stabilization this is destabilization 12. So, it is also 12 d q right 4 other way to say it 2 and 3 is cancelling completely 0 1 2 3 4 times 3 12. So, this is 4 d q this is 6 d q over here it is each of them are 4 nothing is over there 4 times 6 minus 24 d q. Stabilization means usually we put minus that much it is stabilized. So, you can these are number that is called crystal field stabilization energy. So, you can of course, this you know calculate based on this it is 4 or 0.4 I mean if you are saying delta 0 then it is 0.4 and 0.6 if we are calling 10 d q this is 6 d q and 4 d q right. It is very simple math you should be able to do for example, over here case 1 you have low spin case that means, the splitting is high low spin case. So, the stabilization is going to be 5 times 4 5 electrons 4 d q e h or 0.4 delta 0 h. So, it is going to be 20 d q over here it is going to be 0 right. So, this is again it is called crystal field stabilization energy due to this crystal field theory the splitting comes and thereby what is the stabilization energy. You look back to the valence bond theory you do not talk about any stabilization. You cannot talk all the orbitals are degenerate means same energy d x y d x z d x whatever the same energy here you have splitted them therefore, stability and unstability are coming into the picture. That is what is crystal field theory for octahedral.