 we are going to start with yeah the next chapter we are going to start with is periodic properties. Okay so this particular chapter it is basically the first chapter of the inorganic chemistry okay the first chapter of inorganic chemistry. So basically here we are not going to see any numerical questions like we had in some basic concepts of chemistry or atomic structure. You will have a theoretical questions into this right conceptual questions you will get yes there are few things in fact many things you have to memorize here right but certain terms that we are going to understand here like you remember in GOC I have discussed electronegativity concept remember that organic is easy Shastra. Okay then see I don't I don't get this thing you know this concept of easy or tough it's basically something is easy for you and for someone it is difficult because he may he maybe you know probably he did not understand the concept properly. So if you understand the things I know there's nothing tough here but yes there will be you know the nature of the topic maybe like you know there are many things to memorize to mug up maybe that could be a you know the boring part of it that you can say but easy tough I don't get into these concepts it's just you know if you understand it fine if you don't you won't get it right you find it tough maths you know basically the concept is the math is a very vast subject right but you if you like maths you won't be scared of it yes or no so I don't get into this concept of easy and okay try to understand this okay you will get it not a problem organic also if you are if you are finding it tough just give it some time revise the concept that has been taught right and get back to me if you have any doubt right if you run away from the topic that you are not getting in you are not going into the right direction right understand that anyways so in organic chemistry like I said here you know you we are not going to get the numerical questions there are concepts we need to understand terms we need to understand factors affecting it we need to understand that particular terms factors will be using in the entire chemistry whether it is physical especially in organic in organic chemistry we'll use that okay so here we are going to understand for example like I told you we have used a term that is electronegativity that we'll discuss in this chapter okay same thing but a little bit more we'll discuss nothing okay so when you know all these terms then we can uh no normality we'll do after this after this we'll start more concept to there we'll discuss about normality redox reaction and all the concept we'll do over there after this okay this one chapter it won't take much time but I think maybe you know two and a half class requires depending upon it depends upon you like how much doubt you ask that's all so the point is in organic chemistry periodic properties like I said we are going to understand here about the periodic table how the periodic table you know designed what is the you know thought behind this why we need periodic table and then various trend in the periodic table like one thing you must know as you go down the group what happens in periodic table size increases or decreases as we go down the group size increases this trend you know right so these kind of trends we are going to understand here right what are the factors affecting uh the atomic size or ionic size okay those things we are going to discuss okay so the thing is when when they were you know scientists were looking at for different different atoms there were very few elements known right so that point of time what happens uh you know they can understand the property of that particular atom because suppose if you have eight or ten odd atoms known then you can memorize the properties there's no need to arrange them in a proper way so that you can keep that in mind that what happens right but when the time of like when the study goes on and on the research was they were doing various different kinds of research right and that they get to know there are so many different different atoms exist in the nature right as the number of atoms increases elements different different types of elements increases they start they this thing like to keep that you know uh properties and various other things for those particular atoms in mind it becomes difficult and they started looking for the arrangement of atoms in a particular way based on their properties based on their electronic configuration based on their nature many other things right so they started looking for the arrangement of atoms in a particular way so in this way they have given different different theory it is similar to the various atomic models that we had okay various scientists they started looking for the arrangement of subatomic particles and they have given their own theory which we call it as various atomic models so here we have was there are so many elements known so we started looking for the arrangement of atoms so that it is easier for us to keep the keep those properties for a particular element in mind in this way we get different different theories that we call it as the attempt to get the periodic table right and the final arrangement that we have of atoms according to their properties or atomic number basically that arrangement is the periodic table the modern product table we have okay so this theory this entire you know of attempt that is made that we discuss under the development of periodic table right so first of all you see what are the attempts made for the development of periodic table so write down quickly we will finish this because on this you are not going to get any question right so quickly write down development and in the present no the recent syllabus they have removed this historical part of it okay it is not there in the board syllabus that's why we'll go quickly on this okay development of periodic table we cannot ignore this completely because maybe you know in 2022 you know they may ask you these things in the exam j or information must be required right that's why we'll go through it quickly the first attempt was made by the scientists called plots right and this theory we call it as plots theory plots synthesis or plots plots hypothesis not synthesis it's not a plots hypothesis quickly write down what he said he assumed that all elements are made up of hydrogen which was obviously the no wrong not correct but yes we have to go through once he assumes that or he suggested he suggested that all atoms are made up of of hydrogen which was obviously wrong and we discarded right and atomic weight for any element what he says the atomic weight of any element is equals to n where n is the number of hydrogen atom present in it right this is the first theory that we get for the arrangement of atoms the second one is and which is a bit important that is dobernier tried rule dobernier tried rule write down he suggested that he suggested that that within a group of 3 elements group of 3 elements within a group of 3 elements having similar physical and chemical properties similar physical and chemical properties the atomic weight of the middle element the middle element of the middle element is the mean of the other 2 is the mean or average of the other. This is what he suggested. For example, you see atomic weight is the concern. We have atomic weight, not number. Okay, keep that in mind. It is atomic weight. So if you take an example of lithium, sodium and potassium. Okay, the atomic weight of lithium is 7 potassium is 39. So if you take the average of the two, that is 23 is the atomic weight of sodium, and it follows double near triad rule. If you take calcium, strontium and barium, the atomic weight of calcium is 40. And for barium, it is 137. And the average value is 88.5. Right, that is the atomic weight of strontium. The exact, no, it's not for all the things, not true, only for a few groups of elements. Okay, the exact value of strontium, the exact atomic weight is 88. But still it is close. So we can consider this. The exact value is this. Okay, if you see sulfur, selenium and tellurium. Sulfur is 32. Tellurium is 128. So that would be 160. And this selenium is 80. So it is valid for this also. Right, so this is the double near triad rule. Okay, all elements could not arrange this way. And that's why we just started this particular. But yes, it is important in exam also, they have asked this question that which of these groups of elements follows this particular rule double near triad rule. But yeah, they won't ask this. We cannot say next year what happened because we are going to write the exam in 2022. So maybe the things get in place, then they will again, introduce all these things back. So that's why we are not, leaving those things. We can just go through it quickly. Okay, that's all we are doing. In board exam, you won't get this. They won't ask you these things in the board exam, not for sure. Right, third one you write down. The third attempt made was Newland's octave rule. Newland's octave rule. He suggested write down, if the elements are arranged, if the elements are arranged in order to their increasing atomic weight, their increasing atomic weight, then every eighth element, every eighth element, similar properties, similar properties to the first one, the first one, like the first and eighth note in music, like sa-re-ga-ma-pa-da-ni-sa. So sa and sa, the eighth one, sa-re-ga-ma-pa-da-ni-sa. So same thing we have here. If you arrange this atom, you see, we have lithium, beryllium, then we have boron, carbon, nitrogen, oxygen, fluorine, and then sodium. We have sodium here, magnesium, aluminium, silicon, phosphorus, sulphur, chlorine, and potassium. So if you compare this with the musical note, sa-re-ga-ma-pa-da-ni-sa, all these elements have similar properties. Like we have this one, this, similar properties. But yes, this thing was also not fine to be correct for all the elements, and there's no place for inert gas. Inert gas was not discovered, and all elements could not classify it on this basis, and hence we have discarded this. The next one is, the next one is Lothermier curve. Right down here, he plotted a curve, a graph, plotted a graph between atomic weight, atomic weight, and atomic volume, atomic volume of different elements. See, all these attempts made with atomic weight only. Here also we have atomic weight and atomic volume. And he observed a particular pattern, and that pattern is, you see this graph here, the graph is this. Okay, this we call it as Lothermier curve. This is the curve we get. What he observed in this, that the electropositive element, that is the first group, group one, alkali metals. Right, the electropositive elements like alkali metals occupy the peak position on the curve. You see here, electropositive elements occupy the peak position. You see, lithium, sodium, potassium, rubidium, and cesium. Right, these red dots are electropositive elements, electropositive elements. Okay, second observation is what? The less electropositive elements, that is the group two elements, alkaline, alkaline, earth metal, occupy the descending position. You see, lesser electropositive than this one, occupies the descending position, which is this. See this beryllium, magnesium, then calcium, strontium, beryllium. Okay, this red one is the elements of group two. Right, the first one is group one. Lesser electropositive is group two. No, it is not Sashworth. Still, it is not clear. We cannot assure this on this. Okay, metalloids and the transition metals occupy the bottom part of the curve. You see the metalloids and transition elements on the bottom part, vanadium, cobalt, copper, zinc, this side you see, this side you see, metalloids and transition elements occupy the bottom parts of the curve. Right, more electronegative like halogens, chlorine, chlorine, bromine, iodine occupy the ascending position of the curves, ascending position. Right, so ascending position you see here, here we have chlorine, bromine, iodine, somewhere here we have chlorine. Right, so ascending position of the curve, there is halogen atoms present. This kind of pattern we observed, like with a given mass, the volume occupies in this pattern. That is what he said. Right, but the problem with this is that he concluded what with this particular graph, that the atoms with similar properties, elements having similar properties, occupy similar position on the curve. Like all electropositive metals occupy the peak, electronegative occupy the ascending part of the curve. Right, less electropositive, descending part of the curve. This is what he concluded with this. And he suggested right down, he concluded on the basis of Lothar-Mier curve, he concluded on the basis of Lothar-Mier curve that the physical properties of the elements are, physical properties of the elements are, physical properties of the elements are the periodic function of their atomic weight, the physical properties of the elements are the periodic function of their atomic weight. Okay, so this was again, you know, a better result to get from this. And this conclusion actually that the periodic function of the atomic weight the properties are, this conclusion becomes the base of the next attempt, which is Mendeleev's periodic table. Okay, so next you write down the fifth one. Wait, on the basis of Lothar-Mier curve, he concluded that the physical properties of the elements are, the physical properties of the elements are the periodic function of their atomic weight, periodic function of their atomic weight. Okay, this is the conclusion of this, next. Next one is Mendeleev's periodic table. Mendeleev's periodic table, write down, he suggested that, he suggested that the physical and chemical properties of an element that the physical and chemical properties of an element are the periodic functions of their atomic weight. Right, physical and chemical properties are the periodic function of their atomic weight. He's again talking about atomic weight. Okay, so this is important, physical and chemical properties are the periodic function, their atomic weight. Okay, so atomic weight we are dealing with, not number. Okay, he was the first scientist who actually arranged the elements in horizontal and horizontal rows and in vertical column. Right, so the horizontal rows that he arranged here, the horizontal rows are called periods and the vertical column, the vertical column are called groups or called groups. There are, when he give this particular theory, there are total seven periods in the Mendeleev's periodic table, there are seven periods present. This also they ask in exam and if you talk about the row, that is group, there are eight groups. Only 63 elements were known, seven periods and eight groups were present that time. Okay, next write down, each group, just a second, Lotham here was correct. Yeah, it is not wrong. It's correct. It gives us an idea that, you know, the properties had some, it has some periodic order with the elements, but not completely correct because atomic weight he was taking, because atomic weight only Mendeleev's also discarded of some time. Right, but the conclusion that we get, that physical and chemical properties could be in a periodic manner, it may get changed with the elements. So periodic thing was correct, but atomic weight since he has taken, that's why we just started this later, Lotham here. Okay, just a second Pranav, just a second write down, next slide into this, write down each group, each group up to seven, not eight one, up to seven is divided into, is divided into A and B subgroups, subgroups where A is for normal elements, normal elements and B we use for transition elements. B subgroups is for transition element, transition elements. Okay, write down the eighth group, the eighth group consists of nine elements, consists of nine elements in three rows, consists of nine element in three rows, and this we call it as transition metal group. Yes, so Pranav, there are some, you know, discrepancies in this theory and that's why later on we discarded this also, it is also not completely wrong, but again, this is not, you know, valid for all the elements, you could not accommodate all the elements and hence we discarded this particular theory also after some time, but this was the first attempt made in which we get a tabular form of the elements. We can arrange, after this only we started thinking of the arrangement of elements in a table like this. Mendeleev to some extent it is, he was so correct that there were some element for whom the position and properties, for whom position and properties were well defined by Mendeleev even before their discoveries. Okay, he gave this theory and for some elements which was not discovered that point of time, he left the position blank for those elements. Okay, so this was the biggest achievement of Mendeleevs we have, we could find out those things and put left the space blank for those particular elements in its periodic table. But then again with the help of atomic weight, this arrangement of atoms was not finding, was not, you know, observed to be correct for all the elements. There will be some difference in property here and there. So later on, this particular theory was also discarded. So defects is what? There is no certainty in the position of hydrogen, few drawbacks of this point you write down Mendeleev, position of hydrogen is uncertain, drawback of Mendeleev write down, position of hydrogen he did not fix, it was uncertain. Then no separate position were given to isotopes. Last one, the order of increasing atomic weights is not strictly followed. The order of increasing atomic weights is not strictly followed in the arrangement of elements in the periodic table. Yes, yes, yes, fine, but there are other drawbacks also because of that only we discarded this. So the modern periodic table is just a little bit correction in Mendeleev only. Okay, we'll discuss that next class, last point you write down. The order of increasing atomic weights is not strictly followed in the arrangement of elements in the periodic table. This was the drawback. The modern periodic table is what? It is just the modified Mendeleev periodic table. Some corrections we do into this one and we get the modern periodic table. So what is modern periodic table? How the arrangements of atoms are there that we'll discuss next class. Okay guys, okay, thank you guys, thank you so much. Atomic structure guys on Lernist, there are three assignments uploaded, right? It a mixed question. You must solve all those, all the three assignments. Okay, all of you have Lernist credibility, you have credentials, all of you have right, fine, those who did not finish it, finish it by the next class. Fine, okay, thank you guys, thank you so much, take care, bye. Thank you, sir. Thank you, sir. Thank you.