 Hello everyone, welcome to the series of lecture on actinide chemistry and today we are going to discuss about the acuity chemistry of block elements that is lanthanides and actinides. Prior to the lecture I just assume that most of you have gone through the other lectures of actinide chemistry in which the basic ideas of actinide concept bear position into the predictive table and the reference configuration is already discussed. So, I will not go into the details of those concepts. So, first of all I just want to add that these books that I have used for my references and some of the sources that I have taken from the internet. So, I have used primarily this book that is the chemistry of actinides and transactinide elements for my reference in which I have generally considered chapter that is chapter 15 and chapter 23. I have used Medusa header based software for the specification plots. I have also taken some information from internet and web for my this presentation. So, as you already know about the electronic configuration of lanthanides and actinides but just to brief you or just to start the presentation I have shown you the electronic configuration of actinides and electronic configuration of lanthanides. If you see I have also given you the electronic configuration of the trivalent lanthanides and actinides. If you see the lanthanides and actinides what you find common between the two that in actinides when you talk about the trivalent state the f-electron filling goes from f1 to f14 and very similar case arises when you talk about the electronic configuration of lanthanide from 4f1 to 4f14. So, when you see the tri-positive starting from f1 to f14 filling is there but when you talk about the atoms rather than this tri-positive state you find certain differences suppose this one. So, why this kind of differences arises most of these things has been already discussed so I will not go into the detail but one thing I just want to convey you that if you see this they have the occupancy of d orbitals are there what they suggest that the f and d orbitals are close to each other but after that if you see the electronic configuration prefer f and 7s two kind of system. So, if you can see generally that to talk about the actinide then 5fn 6d1 and 7s2 this kind of electronic configuration is preferred when n is equal to 2 to 4 but when you go beyond n is equal to 6 what is there the configuration that is most preferred is fnn 6d0 there is no electron and 7s2. So, this preference goes up to embryo and after that you can again see the involvement of d orbital that basically comes from the upfield shell that is f7 and 4f7 and 5f7. So, with this basic understanding of the electronic configuration we would like to see some of the differences and similarities into the lanthanides and actinides that we all know that when we talk about the actinides and lanthanide the actinide starts from actinium and ends at lorencium whereas talk about the lanthanides they start from lanthanum and ends at lorencium. The filling of epheloprine starts at cerium in the case of lanthanide whereas the filling of epheloprine starts at tritinium in the case of actinides. Most of the lanthanides are naturally occurring except from lithium which is the fission product whereas actinides are generally man made and only few of them such as actinium thorium tritinium and uranium the first two in the series can be found in the miniature. So, when you talk about the similarities as we have seen in the electronic configuration both lanthanides and actinides use f orbital as a part of active valence orbital both lanthanides and actinides when you go from left hand side to the right hand side when you move like this there is decrease in the size. So, that is basically due to contraction. So, we say this as a lanthanide contraction in the case of lanthanide and actinide contraction in the case of actinides. We will try to discuss this again in the upcoming slides. When you see the tri-volatile metal ion if you see these two they have f7 configuration both aluminium and uranium and the trivalent states whether this or this they behave in very much similar way when we talk about the trivalent state in both lanthanide and actinide. But what is the difference this? There are several differences that mainly arise this because the lanthanides use over act whereas actinides use right. The mainly differences arises because they are using different end of shape. The first difference you can say is that 6-D orbiters are energetically accessible. What does it mean that as I have shown you in the previous slides that if you start filling of electron in the early elements of actinide versus lanthanide you can see there is no deorbitant. Where is there is deorbitant? What it suggests that the f and d are close they are energetically very close. So, in actinides these three orbiters that is 5F, 6D and 7S they are energetically very close that I have written in the next slide that 5F orbiters of actinides are in close energetic proximity to the 6D and 7S orbiters whereas if we talk about the 4F electrons they are shielded more effectively than the 5F electron that you can see from this graph also this is the 4F this is the 5F. So, if you see that 5F is more diffused compared to the 4F and if you see the energy difference between 4F and 5D and if you see the 5F and 6D if you see 5F is here 6D is here. So, they have quite good amount of overlap but when you see the other one that is the 4F and the corresponding 5D the overlap is very very small. So, this makes their energy very close to each other. Similarly when we talk about the valency of these actinides because these three are very close to each other. So, you can remove electron either from S either from S or D or F. So, because of this they show variable oxygen state into the aqueous media. So, let us see something about this oxygen state. So, when you talk about these lanthanides they have group oxygen state of 3. What does it mean that most of the lanthanides are having only oxygen state of 3 but if you see the actinides you can start from 3, 4, 5, 6, 7 and sometime 2 also. So, you can see when you talk about the actinides the oxygen states vary from plus 2 to plus 7 whereas when we talk about the lanthanides it mainly plus 3. Why is it like so? Even one more peculiarity about the actinides is the existence of multiple oxygen state at a single time. For example, plutonium you can say most of the oxygen state in the case of plutonium exist at the same time into the solution. How it is possible? To understand that let us see the redox potential of these actinides into the solution phase. So, here I have given you the redox potential of uranium, naphthenium, plutonium and the corresponding couples such as uranium 6 to uranium 5, uranium 5 to uranium 4 and to uranium 4 to uranium 3. And this all is in one volar parabolic acid. So, if we see very carefully the first couple is having a redox potential of 0.06. Next couple is almost 10 times higher and the next one is again going to the negative direction. So, there is a huge difference from uranium 6 to uranium 3 couples. When you see the naphthenium case again you can see the naphthenium 6 is plus 1.136 whereas naphthenium 5 to 4 is 0.739 and again it is getting reduced to 0.155 in the case of naphthenium 4 to naphthenium 3. So, again you can see there is a difference. What about the plutonium? The first one is from plutonium 6 to plutonium 5 is 0.916. Second one is hardly 0.25 minutes ahead that is 0.1.17. Second one is very close again 0.98. So, even this one if we directly going from plutonium 6 to plutonium 4 again it is in the range of 1.043. What it means that most of these redox potentials are very close to each other. What does it suggest that most of these pieces can coexist at a given solution condition. So, it connects through this kind of particular behavior that sometimes the overblasting oxygen sheets are also possible for a given element. We will all we will now see that how the individual oxygen sheets are varying as I have shown you that the definite can have plus 2 to plus 7. What are the elements that exist in plus 2 and obviously plus 3 plus 4 to plus 7. So, first off we will talk about the zivalent ion. The only possible or only attempt that prefer this state is novalium. You can see here and along with this I have given the electronic configuration in the m3 plus state. So, it is the mp state that is given at 30. Suppose I go to m group. So, the extra stability of this is coming because of the f14 configuration that is a closure configuration. But the same is not true if you see the corresponding lengthenite. In lengthenite if you see the terbium it does not prefer plus 2 it is not prefering plus 2 it is prefering plus 3. That can be explained just by looking at the record potential. If you see the plus 3 the plus 3 to plus 2 that the redox potential if you see it is highly positive plus 1.45. So, the energetically this transformation is very much favorable. So, the tendency of novalium going to 2 from 3 is very much favorable. But if you see the terbium terbium 3 to 2 it is negative and the corresponding delta G for this should be positive. So, this kind of transformation is very difficult that explains that why terbium 2 is not stable. Although one can see that both of these when you talk about the novalium and terbium they have electronic coordination that is f14 when they are in the diagonal state. So, what it means that rather than the stability of f14 that is the closure configuration there could be other factors that decide the stability of the metal ion into the aqueous phase that may be related to the electromagnetic effect that is very much different from the 4s orbit and the 5s orbital or due to the interaction of these orbitals into the aquatic media because of which the optional states differ from 2 to 3. When we talk about the trivalent cyan starting from amyrecylium to medallivium everything can be present in the trivalent. So, you can see amyrecylium to medallilium along with amyrecylium they can be trivalent. But if you talk about the lower part that is plutonium, nectonium, murinium, protectinium, orthodium there is very much difficulty in preparing the trivalent state. In plutonium you can prepare trivalent using some reducing agent, but the moment you prepare they tend to oxidize to plutonium 4. Most of the time this happens because of the radiodesis of the water that will be there because when we see a plutonium solution we know that it will give some alpha particle and this alpha particle has tendency to do some radiodesis and because of that radiodesis we produce several ions and several radicals that are very reactive they can be oxidizing they can be reducing. So, it so happens that whenever solution of plutonium 3 which is giving you continuously some alpha particle that lead to radiodesis of the water and producing this kind of very reactive species the plutonium 3 get oxidized to plutonium 4 because of the radiodesis. To confirm that what people have done that they use the plutonium that having a very large half life such as plutonium 242 or 244 and but they have seen that when you are using this plutonium where the half life is squared up it means the alpha emission is low then their stability in the plus 3 is quite large as compared to the plutonium isotro where the alpha emission is very frequent or you can say is half life is very small. When you talk about the methoenium and uranium again they are very difficult to stabilize and most of the time they require inert atmosphere for the stability. Thorium and plutonium they are almost very very difficult to form and they are not even stable in the solution phase. Let's talk about some tetravalent ion so when you talk about the tetravalent starting from thorium to californium everything can be prepared in the tetravalent form but if you talk about this stability the most stable one is thorium and plutonium. The other parts such as plutonium uranium and sodium they can be made stable but they require absence of oxygen but plutonium 4 is obviously stable and even in the presence of oxygen it is quite stable. The other actinide that is stable is barchelium you can see from here that is stable because of the F7 configuration of plus 4 states so that is extra stability comes because of the F7 configuration in the case of barchelium and as I have shown you in the last slide all the plutonium is stable in plus 4 but that is not the only option state that is there in the plutonium solution. All the oxygen states starting from plus 3 plus 3 to plus 6 can coexist in the case of plutonium. When I talk about the other elements such as emerycium, curium and californium they are very difficult to prepare in the plus 4 and even if you try to prepare them using some reducing condition you need strong complexing agents such as chloride or phosphate to get sterilizing to the plus 4 states. Let us see about the pentavalent ion again you start you can see that from plutonium to emerycium they can be made into the pentavalent state but the stable pentavalent is plutonium and neptonium rest all are very much unstable and the most of the time this instability comes from the disproportionation what is disproportionation that I will just discuss in the next slide so they are unstable with respect to the disproportionation. When I talk about the hexavalent ion again from uranium to emerycium they all can be prepared in the hexavalent state and the most stable one is the uranium that if you see uranium is stable that is because of the F0 system if you see uranium 6 doesn't have any electron in the upper beetle and if you talk about the relative stability again uranium 6 is very much stable compared to plutonium 6 which is stable compared to neptonium 6 and that can directly be seen from the corresponding red dot function if you see the relation from 6 to 5 is not very much feasible it is only 0.063 so delta g is not very feasible but we talk about from neptunium 6 to neptunium 5 this is very much feasible so that explains the trend that why neptunium 5 is so stable and uranium 6 is so stable when we talk about the hexavalent state or the plus 7 states the possibility is neptunium and plutonium that too in the alkaline medium in acidic medium they do not exist as a hexavalent ion so with this information of different kind of oxygen state into these aquatic media let us try to see that because as we know that the stable states are from plus 2 to plus 3 1 in the actinite and in different set of conditions some of them have a different structure altogether let us see how they differ so as I told you that for actinites you can have from plus 2 to plus 7 but ions in plus 2 plus 3 plus 4 they are spherical but what about plus 5 and plus 6 so when you see it's plus 5 and plus 6 they are not existing as a spherical ion because here the any potential of plus 5 and plus 6 is so high that they expect the oxygen from the media and they make this kind of linear compound which are known as linear dioptocatase you can see here the pentavalent this actinite is obviously having pentavalent state so you can say pentavalent minus 2 here and oxygen minus 2 is total charge plus if you see the hexavalent obviously plus 6 minus 2 minus 2 so they exist as a linear dioptocatase but not all pentavalent this is mainly true for actinium onward what about the pentavalent state of actinium this does not exist as this the most stable form of this is monoxy with either one or two heteroxial group and depending on the number heteroxial group the oxygen can be again state of the total is can be plus 2 to plus 1 so this difference that exists that although this is the most stable state of actinium so like methenium but this doesn't exist as dioptocatase because the formation of the dioptocatase is very very difficult because of the some symmetry of orbiters and they cannot make these five warnings with the oxygen the second oxygen basically and they prefer to remain in this form when I talk about the actinium obviously as I told you that they are only stable in the offline media and the form in which they are stable is actinite 4-4 ovex 3 minus so we know that yes these are the states and these are the basic forms you can say that the stability forms in the extra space and some of them are existing as a spherical and some of them are existing as a linear hand we say that if you linear hand like this you are actinized and the corresponding either class or coupler depending whether they are pentavalent or hexavalent so let us see as I told you that most of the line the pentavalent states are very much unstable because of the term called disproportionation what is this proportionation this proportion is nothing but you start with the one oxygen state let us say five and that will result into two oxygen state that is plastic it is the splitting of one oxygen state into one higher and one lower oxygen state that is very much common for the pentavalent iron as you can see uranium, neptunium, plutonium all of them undergo disproportionation and if you see the equilibrium constant that is very very high for the uranium compared to neptunium that again suggests that neptunium 5 is more stable compared to uranium 5 and when they disproportionate what they are forming is a lower oxygen state that is uranium 4, uranium 6 similarly when you talk about the neptunium then you talk about the neptunium that is NPO2 plus it will take up 4 proton from NPO2 plus plus 2 H2 so neptunium again starting from 5 going to 4 N2 6 so this is this proportion that is mainly happening for the pentavalent but there are other ions also as this you can see the two oxygen states are combining to give two new oxygen states but this is very common in the actinides that this proportion reactions that is there for the actinides so now with the knowledge of the exact spherical or linear ion in the actinides in their oxygen states let us talk about how the sizes of these ions are varying as I told you there when you talk about plus 2 to plus 4 they are mainly spherical and when you talk about plus 5 plus 6 they are mainly a linear ion so here we have seen the ionic radii of the actinides as well as lanthanide ion in plus 3 and plus 4 are not going for the plus 5 because they are not spherical they are basically linear compound if we see that there is a steady decrease whether we talk about the lanthanide or we talk about the actinide there is a steady decrease in the ionic radii of this with the atomic number 5 because when we talk about the lanthanides this 4F or in the case of actinides this orbital they contribute to a very poor shielding and because of the poor shielding whatever electrons we are adding when we are going from air to air they are feeling more effective charge and because of this there is a contraction and this is linearly decreasing and why the size is different from lanthanide to actinide obviously we are going from 4F air to 5F so the size is on the higher side again in the tetravalent also you can see there is a steady decrease in the size because of the contraction so this is the steel lanthanide or actinide contraction that basically happens because of the poor shielding of where we work on by airport brittle one more very interesting effect that is very important when you talk about the heavier atoms is called relativistic effect what the effect is when you are in the in the zone of this high atomic number that is actinium sodium or put actinium such a very high atomic number what will happen that we have a nucleus right and the electrons are revolving around them so when you are increasing this atomic number the electron will more and more pull from the nucleus and its speed keeps on increasing when you go through a very high atomic number such as in the lanthanide or actinide this attraction is so much that the speed goes close to the speed of light and when the speed goes to the close to speed of light there is something that is called the relativistic mass that is different from the dashed mass and if you compare them where your v is going close to see your relativistic mass of the electron keeps on increasing and your relativistic mass and your Bohr radius are inversely proportional when the mass is increasing the Bohr radius when the mass is increasing the Bohr radius is contracting and this effect is very much prominent to S and P orbitals so you can say the S and P orbital will try to contract but when we talk about the other two that is D and F they feel opposing effect why because since S is getting contracted and P is getting contracted now the shielding of nucleus or the shielding of nuclear charge for the outer electrons are very high so they contract and they shield the outer orbital because of that D and F do not feel that much amount of attraction from the nucleus and instead of getting contracted they expand so this is something called direct relativistic effect and this is something we say like indirect relativistic effect the same thing you can see in the figure that happened actually here we do not talk about the S and P if you see if I am considering the relativistic domain and non relativistic domain in the non relativistic domain the orbital is here but the movement we apply this relativistic correction the orbital shifted then you can see the P orbital this is non relativistic and this is relativistic you can say there is a shift towards the nucleus but what about the F and D the non relativistic is this side whereas the relativistic is shifted towards right so there is a destabilization of because the destabilization of D and F whereas there is a stabilization of S and P because of this relativistic effect also the contraction of the lengthenance and actinate occur and almost 10 to 15 percent of the lengthenance of the main contraction can be attributed to this relativistic effect so when you talk about this linear ion there obviously I will not talk about this contraction in sizes because the linear ion that is pentane is developed they are basically existing as the linear ion so this is by dexavirant and similarly I can write for pentavirant also and there the concept of this reduction in the anachronism we are not going to discuss because they are linear they are not spherical and this concept is mainly we are discussing about the spherical ion so the first thing that can happen when you have a metal ion you know about this size you know about the radius and you put them into the what will happen they will try to hydrate themselves what can happen if you have a metal ion you put into water there can be a primary hydration layer just on the metal ion that is they have given an H2O and it can be a putter hydration which includes both primary and the secondary that have given the name H that is obviously primary plus secondary so the moment you put there are hydrogen structures around this metal ion we will talk about the trivalent metal ions and what are the hydrogen structure around the trivalent metal ion we can determine this hydrogen structure obviously because we need to know that how many are in the primary sphere and we want to know that how many is there in the secondary sphere or if we can get information about the total we can get secondary just by subtracting the primary one from the total so there are two techniques generally people use to get information about the primary hydrogen sphere that is fluorescence and exhaust whereas to get information about the total you are mainly relying on the electrophoretic mobility kind of experiments in which we measure some kind of diffusion which will tell about the overall radius of the structure and since we know about the radius of this we will try to redo and deduce that what is the total hydration and from this total hydration we subtract primary hydration that we can directly get from these techniques and we can get the value of the secondary hydration number so now how these hydration numbers are changing for the trivalent metal ion if we see the trivalent metal ion and you start from this and this is shown here the initial hydration level shows almost nine water molecules but the moment you go from left to right what you see there is a decrease and start from nine and get settled down eight why there is a change from nine to eight when we are at this position obviously as shown in the previous slide so since the sizes are large they can accommodate and so size is a bit larger you can accommodate almost nine but the moment you move like this your size keeps on reducing so now because of the steric factors accommodating nine water molecules are very difficult so they settle down with eight and the very similar case happens with the actinates also and this transition when you see this particular area that happens for lanthanides at promethium and dysprasium whereas for actinides it happens at americium to anesthenium why this smooth transition because at this particular place whatever metals are coming such as the first americium here they can have both some of them can have nine as two some of them can have eight as two so the hydration space can have nine or eight so they have this kind of mixture and because of that they follow this line what about the secondary hydration if you see the secondary hydration this is just reverse although the primary is decreasing from nine to eight is secondly when you are going from cerium to tervium this keeps on increasing why so because as we are reducing the size but we are not reducing the charge everyone is struggling so the z by r ratio or you can say the ionic potential is keeps on increasing and although because of their particular size they cannot accommodate more water into the primary sphere but because of their electrostatic field that can extend they can now accommodate more water molecule into the secondary sphere if you show up the secondary sphere and they totally obviously on the larger size so here comes the role of ionic potential that is the surface ionic potential and this happens because of the again when you talk about the tetravalence in tetravalence such as thorium we are having generally 10 to 11 water molecules what about pentavalence the case of pentavalence again as I told you that little special when you talk about pentavalence and hexavalence because pentavalence do exist as a linear time that action here and the positions that we say the axial are already occupied or already blocked by the oxygen and you are only left in the equatorial plane when we talk about this then the chances of water coming into the plane of this neptunium is restricted in the equatorial plane only and generally 5 to 6 water molecules are present in the actinide when you talk about the pentavalent actinide or pentavalent actinide one very interesting aspect that is very much peculiar to the it may sort basically to the pentavalent ions are cation cation interaction when the concentration of these actinides are very low then obviously they exist as a high little ion but suppose you have a medium in which you are having both neptunium 5 and urinium 3 suppose you are having both so urinium 6 obviously that is q22 plus and q22 plus both are linear cations so when they are present together the chances are there that the cations can interact with each other and the more in which they interact one is called t shape and one is called diamond and these kind of shapes are very very common in the solution why the interaction is taking place why such a interaction is there to understand that you can think of the concept of residual charges what is the residual charges although I have shown you that the pentavalent actinide that we write as a n o2 plus we say they are pentavalent but since they have oxygens here and oxygens donate part of their electron density to these actinides it so happens that if you see the charges on the actinide they are not exactly pentavalent they are not exactly 5 or 6 what happens that if you talk about neptunium let us say np42 plus and if you see the charge on neptunium exactly it play around point 2.2 whereas if you see about the urinium you do 2 plus and you try to see the charge on urinium then they belong plus 3.3 so these charges are different than whatever we say that whether they are pentavalent but which is the actual charges it is basically 2.24 pentavalent and 3.34 hexavalentine and now since the charges are different this again has some partial negative charge and this partial negative charge can interact with a positive charge of pyridine which is 3.3 and they can make this kind of complex which is known as cation cation complex and it is very very unique properties of the actinide that catamphetam formation not with urinium only you can have other metal ion also for example you can have thorium also and as the charge is increasing the interaction is getting stronger and stronger so with this I want to end this particular lecture and we will discuss about the other concept in the next coming lectures thank you very much