[Music] hey all welcome to home school and welcome back to class live in chemistry series we have completed first two chapters in class 11 that is basic concepts of chemistry as well as structure of atom in a detailed way all concepts are covered in a detailed way say concept clarity is very very important to attend the competitive questions of any exam it may be need je or whatever it is let me finish all the chapters and their concepts in detail and after that i will come up with uh the objective questions on important topics okay say today i am with the third chapter that is classification of elements and the periodicity in properties okay so this is nothing but we are learning entire things about the periodic table okay so it's a very fundamental chapter uh it's very much essential to understand each and every concept of this chapter because this will help you to deal with every other chapter that is there in class 11 and class 12 chemistry so it's very important to understand you may not get too many questions from this chapter for competitive exams but understanding the concepts of this chapter will definitely help you in understanding other chapters in a better way okay so try to understand every concept of this chapter i'll be explaining you all in detail okay so let me quickly tell you what and all you will learn in a chapter first and foremost you will learn something about history of periodic table okay say uh can you all tell me how many elements are there in our nature as of now see as of now we have around 120 elements there are around 120 elements okay but in many of the periodic tables that you find it in your textbook there were 118 elements or in some textbook 116 elements okay but as of now there are 120 elements all of them are not naturally existing few are artificially made elements okay so both artificial and natural together we have 120 elements and when we have to study about these elements we need to have a particular pattern okay see scientists have already studied about these elements and they have arranged these elements in the form of beautiful table called periodic table okay so uh so that it's because of this periodic table study of chemistry has become more comfortable and convenient otherwise you know what we can't study every element in detailed way and even when you study you can't remember all of them right say how is it possible to study every single element in a detailed way it's not that possible and it's not convenient also so you know we study these elements in group buys okay see there are some elements which look similar which behave similar so all of them we study together okay we no need to study every single element all of them the elements which are present in one single group are studied together we will understand their properties together because almost all of them will show similar chemical properties almost 80 percent of their properties will match with one another so all of them we will complete it at one stretch okay so this way we will study the elements of you know periodic table so periodic table made the study of chemistry more convenient i can say because of this uh you know arrangement very beautiful and arrangement follows a particular concept okay so all of that we will discuss in detail so in a periodic table like you know and and this periodic table that we are following currently is called modern periodic table before this modern periodic table scientists have introduced many more periodic tables almost around 45 periodic tables are there okay so and and these periodic tables you know had one other limitation so we can't follow them taking all the good from these periodic table our modern periodic table was introduced so to understand modern periodic table we need to understand something about these periodic tables that were there before our present periodic table okay so we are not studying all the periodic tables which were introduced uh previously i mean as a history you know we particularly study four periodic tables okay as history what we can call it as genesis okay so genesis in the sense what history so how we how is our modern periodic table actually came into existence before that we were having so many periodic tables and and what were they and all of them we are not studying i told you already right we are studying only four periodic tables that's important okay so the first one is dobrenner's law of triads the brainerds law of triads and the second one is newlands law of octaves and the third one mental use periodic table and the fourth one is lother mayor that is lotter major periodic table this will not be mentioned in our textbook but it's nice to study this periodic table also so after new land comes lothar meyers after that you will have mendel use periodic table and after studying all the four we will go for modern periodic table and this is one part of a chapter and about a modern periodic table you know we study so many things about modern periodic table say uh how this modern periodic table is classified on what basis uh the periodic table is classified all that we will discuss in detail and after that we will study something called periodic properties periodic properties will try to understand uh the meaning of the word periodic properties in detail in the later videos say under periodic properties we study about atomic size ionic size ionization enthalpy electronegativity valency electro positivity and many more things so each and every property we will have to discuss in a detailed way right so this is something about the chapter that we are going to study and in today's video i am going to complete the entire genesis all the four periodic tables i'll discuss okay so how these periodic tables were introduced what were the merits of these periodic tables what are the demerits all of that we will discuss in a detailed way and quickly let us go for the first periodic table that is darbreener's periodic table okay daw breeders dawbriners law of triads bc okay and you must understand the meaning of the word triad try in the sense three okay ads it means group so triads is nothing but group of three group of three and during darbriner's time almost around 16 elements were discovered out of 16 elements dobrenner could give arrangement for only few elements actually that was the greatest limitation of dobrino's triads and uh let's understand on what basis dobriner gave his periodic table it is on the basis of he arranged the elements on the basis of atomic mass atomic mass okay so he arranged the elements in the increasing order of atomic mass and he followed one principle he observed one thing in his periodic table that atomic mass of middle element was the average of atomic masses of first and third okay so this is very very important atomic mass of middle element middle element was the average of was the average of first and third elements okay so you will understand once i give uh his triads you know what he mainly gave three triads for us this is triad number one this is triad number two and this is triad number three in the first triad he arranged lithium sodium and potassium in the second triad you will find calcium strontium barium chlorine bromine iodine so these are called as you know dobrenner's law of triads even in your modern periodic table you know the first triad is present like this only i mean after lithium you will have sodium after sodium you have potassium okay even even calcium strontium barium also are arranged in the same pattern right so you will find this triads even in our modern periodic table and see he arranged these triads in the increasing order of their atomic masses atomic mass of lithium is seven okay atomic mass of potassium is 39 okay and what he says is the atomic mass of middle element is average of first and last i mean if i have to find the sodium's atomic mass i need to take average atomic mass of lithium and potassium so what is lithium's atomic mass 7 what is potassium's atomic mass 39 7 plus 39 by 2 if you do sodium's atomic mass you will get that is 23 so sodium's atomic mass is 23 okay so like that in every triad the middle elements atomic mass is average of first and last so this is the main point that you need to remember about darbriner's law of triads okay but during his time 16 elements were there but he could not give justice for all the 16 elements based on this principle he could arrange only these elements in a proper way okay so that was the greatest limitation of dobryner's law of triads so nothing much to discuss about this let's quickly go for newline's law of octaves coming to newlands law of octaves this is also very very simple even this periodic table uh was designed on the basis of increasing atomic mass on the basis of increasing atomic mass okay so just like dobriner this fellow also followed atomic mass is the property to decide the arrangement of elements okay see let me first show you his periodic table see he started with hydrogen we know atomic mass of hydrogen is one next element he arranged was lithium and lithium's atomic mass was seven right and after lithium he arranged for beryllium after that boron then carbon nitrogen oxygen then he came back here and he has put fluorine here okay and below lithium he has put sodium then comes magnesium aluminium okay here silicon here phosphorus here sulfur then he arranged chlorine here after that potassium okay calcium chromium titanium manganese and he went on like that okay so this is how we arranged the elements based on atomic mass atomic mass of hydrogen was one lithium is seven uh beryllium you will find 9 boron 10 carbon 12 nitrogen 14 oxygen 18 right so sorry oxygen 16 like that atomic mass increasing order you will find image arrangement and what he also found was every eighth element was similar to the first element if you consider lithium as the element okay first element then with respect to lithium which is the eighth element if this is one two three four five six seven eight so with respect to lithium sodium is eighth element like that with respect to a beryllium which is the eighth element magnesium with respect to boron which is the eighth element aluminum with respect to sodium which is the eighth element potassium right so what he found was every eighth element was similar in the properties okay that means sodium is similar uh just like lithium uh our potassium behaves in a similar way just like sodium like that he found a similarity between first a particular first element and its eighth element okay so that is why his periodic table was called as octaves octaves in the sense what uh you know musical notes so we know the musical notes right the knee indian musical note see this is our first note which is the eighth note against so first note is similar to the eighth note just like that for a particular element uh the properties are similar with eighth element its eighth element okay so for carbon which is the eighth element silicon with respect to nitrogen which is eighth element phosphorus so that is why this was called as law of octaves okay so that is important point guys so what i can write here for a particular element or i can write this way every every eighth element is similar to is similar to a particular a particular first element first element okay so this is the main principle of double sorry new lines law of octaves i can tell fine everything is fine and now let us discuss its limitations limitation so the major limitation is his principle what is this principle every eighth element must be similar to the particular first element right his principle holds good only till calcium okay so this principle i mean his theory is applicable it is applicable only till calcium okay you see with respect to magnesium calcium right calcium's properties must be similar that is okay but you see chromium below aluminium he has placed chromium but whereas chromium's properties are entirely different from aluminum titanium is placed below silicon titanium is very much different than silicon manganese he has placed below phosphorus whereas both are very much different so his theory is applicable only till calcium okay so after calcium whatever he has arranged to know they have actually deviated from this particular principle they were all having very much different characters compared to the first elements okay so that is the greatest limitation and the next one is two elements he placed in a single slot okay i mean to say if you uh come to this side i mean first group so below chlorine or below bromine he has placed two elements together okay say for example cobalt and nickel he placed together right say this is another you know limitation you can see so two elements two elements placed in a single slot in a single slot okay so he could not give any reason why he placed two elements together in one single slot they they should be placed differently right in different uh positions but they were together for that he could not give enough uh justification and next one is he did not give any gaps for newly discovered elements see uh during his time there were around 50 plus elements discovered he has given place for those 50 plus elements but what about the newly discovered elements he could not give any place he could not provide any gaps in his periodic table for the newly discovered elements so that is another limitation of newlands law of octaves okay so this is all about law of octaves now we will go for lother mayor's periodic table see guys lotha meyer followed very different method for the arrangement of elements uh actually what he has done is he has plotted a graph between atomic volume and atomic masses okay so atomic volume is nothing but density so elements density versus atomic mass so that is the graph that i have shown it here see one thing you can observe is you see lithium sodium potassium rubidium cesium okay let me let me write it here lithium sodium potassium rubidium cesium so where are they located in a graph they are located at the peaks right so these guys are actually located at peak peaks of a graph or a curve right so that means all these elements must have had same properties that's why all of them occupy peaks isn't it so he he said that yes these elements belong to one particular group okay you can you can study them together because when he has plotted a graph all of them occupied you know peaks and he called these elements with the name alkali metals okay so all alkali metals occupy the peaks say for the competitive question position of elements can be asked say in lotha mayor curve what was the position for alkali metals so what was the position here the position is peak right so the peak of the curve uh is occupied by our alkali metals right so this is the first point you have to remember now the second point okay let me talk about this you see beryllium okay and this is magnesium calcium strontium and barium see they are they they are occupied in a same position i mean on a descending curve right so what is this the point you see from here the curve has gone like this descending this point and this point you observe descending position again this magnesium descending curve calcium descending line strontium descending line barium right so the elements which have occupied the descending curve okay so elements elements on descending curve descending curve are nothing but alkaline earth elements alkaline earth elements so these elements behave in a similar way so which are the elements beryllium magnesium okay calcium strontium and barium so all of them occupy the uh you know descending curve okay i mean the downward curve and now you see upward curve up upward curve is what this one this is upward curve okay say upward curve fluorine upward curve chlorine upward curve bromine upward iodine right so what i will call it as ascending curve okay elements elements on ascending curve which are the elements he called these elements as halogens okay so uh your fluorine chlorine bromine iodine so all of them have occupied ascending ascending curve okay so all of them must have had same chemical and physical properties and finally you see bottom of the curve okay lowest peak lowest peak is occupied by you know the transition elements okay uh the elements which we can call it as metalloids right so actually in the modern periodic table you find these elements uh in between s block and p block or we can call them as d block elements okay so rest of the elements p block elements and d block elements have occupied you know the bottom peak so p or i can say d block don't worry about this what we will study in modern periodic table so d block elements are found at bottom peak bottom peak so what is important to remember is position of elements so where are alkali metals located at the peak okay so where are uh you know alkaline earth elements located in the descending curve where are halogens located in the ascending curve where our d block elements are located in the curve at the bottom peak so position you have to remember here okay so this is how based on their common position he could tell that yes these these elements have common properties you know that's how one can come to conclusion right so that is all about lotta mayor's curve and you know what see only based on a curve we can't decide uh the similarity of properties between the elements you know there are many limitations here you see here if you see boron aluminium they belong to one group actually in the modern periodic table whereas lithium and rhodium have very much different properties compared to boron and aluminum like all these guys do not show similar properties in fact right so like that there are many limitations for lotha meyer's periodic classification also okay and now let's go for mendel use periodic table which is our very much previous periodic table for our modern periodic table okay so many points we can take it we we can find similar between modern periodic table and the mental use periodic table let's understand mendel use periodic table in a detailed way see guys mendel use periodic table gives very important idea for modern periodic table see mendeley also arranged all the elements according to atomic mass okay so he also arranged the elements on the basis of atomic mass and here is a very very important sentence that you need to understand there is something called mental use periodic law okay so just like modern periodic law there is a mental use periodic law it says that the physical and chemical properties i'm just writing a short form okay so phy in the sense physical properties physical and chemical properties of elements okay that means physical and chemical properties of elements depend on they are periodic functions periodic functions of their atomic masses okay so it means that physical and chemical properties depend on atomic masses okay so that means the elements which have same physical and chemical properties gets repeated after certain intervals i mean after some atomic masses okay say if if you have the element number one here see after some atomic masses again the element with the same physical property gets repeated okay so first element is placed here then the other element comes here next element comes here next element comes here i mean all these elements which are there in a group must have had same physical and chemical properties so between this element and this element there are so many other elements with different atomic masses right so that is what the meaning see the elements with physical and chemical properties gets repeated continuously after certain atomic masses okay so that's what the meaning of this particular sentence fine and you know uh the concept of groups and periods are introduced by our mendeley so he arranged his periodic table in seven periods seven periods and eight groups okay so you must understand what do you mean by group here group is nothing but vertical column okay vertical column is called group horizontal row is called you know period horizontal rows are periods vertical columns are groups so let us just quickly roughly draw mendel's periodic table so this is our first group okay so this is a first group this is our second group third group fourth group fifth group sixth group seventh group okay and this is our eighth group like this you know there are eight groups eight vertical uh you know columns in mendel's periodic table and seven horizontal row okay so this is period number one period number two three four okay five six seven like that so very very roughly i am showing you right okay and now listen carefully each and every group is again subdivided into two groups group a group b you see this is our first group first group is again subdivided into two subgroups that is a and b like that our second group is also divided into a and b third group is divided into a and b fourth also divided into a and b like that fifth also sixth also and seventh also so till seven groups each and every group is subdivided into a and b okay so a subgroup b subgroup in first group like that in second group a sub group b subgroup like that till seven group you have a b sub groups whereas eighth group will not have some groups okay and there are some elements placed in a subgroups okay for example in the first group if you come you have an element hydrogen lithium okay uh sodium potassium rubidium cesium right so very very roughly i am showing you and coming to the b sub group you have an element like copper you know all d block elements will come here right and and actually there is no connectivity between a subgroup and b sub group usually the properties of a sub groups are entirely different from the properties of b sub group this you keep it in a mind okay so actually this is one of the limitation of mental use periodic table i can say okay properties of b subgroup is entirely different properties of a subgroup is entirely different but whichever the elements are there in a subgroup all of them will show same chemical and physical properties okay whichever the elements present in a b subgroup all of them show same chemical and physical properties right so this is how we have eight groups and seven periods and now once mendeleev has given the entire periodic table noble gases were discovered okay so he had to give some place for noble gases so he introduced uh the you know ninth uh group that he called it as zero group so this is zero group in this zero group you will find the noble gases helium neon argon etc okay so zero group includes our noble gases okay so uh what actually he did was he studied each and every element you know during his time almost around 60 elements were discovered he studied each and every element in a detailed way you know what every element he made it to react with oxygen and hydrogen okay so he conducted reactions of elements elements with oxygen and hydrogens oxygen and hydrogen okay so whichever the elements on reacting with hydrogen uh when they have given uh this particular formula you know for hydrides all of them were placed in the first group okay and when they reacted when these guys when the elements that were placed in the first group when they reacted uh with oxygen they gave the formula m2o type of oxide okay see all these elements why did he put in group one actually when they reacted with hydrogen they gave this kind of hydride this formula having hydrate and when they reacted with oxygen they gave this formula this particular oxide okay and similarly these guys when the elements when he has placed the elements in the second group all of them when they reacted with hydrogen they gave this kind of hydride and similarly when they reacted with oxygen they gave this kind of oxide m in the sense what any element in group 2 okay like that based on the reactions with hydrogen and oxygen whatever the product he had got no so based on the formula of that product you know he arranged the elements into several groups and periods so whichever the element that has reacted in a similar way with oxygen and hydrogen all of them he has put in one single group okay so this is a a major thing that he had done uh for introducing his periodic table right so all that is very nice and one more good thing he has done is he left gaps here and there okay for example you know what uh boron imagine if boron is here so below boron he left a gap and he called that gap as ekka boron okay like that you know what below silicon also he left a gap and he called that gap as a car silicon silicon similarly below aluminium also he left the gap and he called with the name ekka aluminium okay actually these are not the real positions okay just for example i'm showing so below boron he left a gap below silicon he left a gap below aluminium he left the gap okay so not only below these elements you will find gaps in its periodic table frequently like after few elements it's because these gaps are because if newly discovered elements are there you know they can be placed in the gap according to their properties okay so if the element uh is showing similar properties with group one then in group one here and there some gaps are there so you can place the element in that gap so depending on what physical and chemical properties are there for a new element you can give place for newly discovered elements also so that is the main purpose why he left gaps in the periodic table okay and you know what see below boron he called the element as ekka boron eka means what the meaning of the word eka means one okay or save it means that this element in this position you have to place an element which shows similar characters with boron okay so here what do you mean by eka silicon you know there is an element which can be discovered newly and that element shows similar characters with that of silicon so you have to give the position for that element here below silicon that's what the meaning of the word eka silicon so actually uh eka silikan is nothing but germanium okay so germanium was discovered during that time and people were studying its characteristics still they have not confirmed that it will have a similar characters with silicon but this person predicted that germanium can be similar with silicon so he gave a place empty below silicon and he called that germanium as echa silicon still name was not given for germanium okay but he predicted mendeleev predicted that it can be similar with silicon so he left a gap below silicon and called germanium as eka silicon okay similarly echa aluminium is nothing but gallium okay so gallium was also discovered uh during his time and still name was not given and he predicted that gallium can be similar with aluminium so it has to be placed below aluminum so still name was not given right so he called that gallium as aluminium echa means one same or one similar okay uh so that's what about the gaps that he left in his periodic table so this is a very good thing that mendeleev had done uh you know if any new elements were discovered in the future so all this is about mendel's periodic table and now let us study about the limitations of mental use periodic table these limitations are very very important to understand see the very first limitation that i will be discussing is about the position of hydrogen so what i can say is position of hydrogen is uncertain hydrogen is uncertain uncertain in the sense what doubtful okay so he could not confirm the position of hydrogen actually i have written hydrogen here but in his in his original periodic table you don't find hydrogen here because there is a controversy in deciding the position of hydrogen because hydrogen shows similarities with alkali elements like lithium sodium potassium rubidium they are called as alkali elements hydrogen shows similarities with alkali elements and it can also show similarities with halogens halogens are nothing but fluorine chlorine bromine and id okay so he was in a confusion that where to place hydrogen whether to place it with alkali metals or to place it with halogens so this was a big doubt so that is the reason he could not give justice for the position of hydrogen so that's why we say the first limitation as the position of hydrogen is doubtful that is uncertain okay and the second one is very importantly no position he did not give any position for isotopes so we all know what do you mean by isotopes right isotopes are nothing but elements okay atoms of same element you know they have same atomic number but different atomic mass see carbon 612 carbon 6 13 carbon 6 14 like that okay so isotopes are actually atoms of same element you know atomic number is same atomic mass is different this guy has arranged the elements according to increasing order of atomic mass say if if he arranged lithium here he has arranged you know beryllium here boron here so after that the you know like that in the increasing order of atomic mass he has arranged all elements that means if he has arranged carbon 12 here carbon 13 must come here carbon 14 must come here because atomic mass of carbon 12 is 12 atomic mass of this carbon is certain atomic mass of this carbon is 14. so almost every element has isotope okay so if you come to nitrogen nitrogen 14 is there nitrogen 15 is there nitrogen with atomic mass 14 nitrogen with atomic mass 15 okay like that if you come to oxygen oxygen 16 is there oxygen 18 is there right so every element has isotopes so the isotopes also must be placed when he considered atomic mass because isotopes will have different atomic mass with same atomic number right but he did not mention isotopes of any element in his periodic table when he considered atomic mass he must have mentioned isotopes also but he did not mention any isotopes right so that is another greatest limitation and coming to the third point okay you will find somewhere that you know tellurium is placed after that iodine is placed actually tellurium's atomic mass is 120 iodine's atomic mass is 126.9 you see iodine should come here tellurium must go there right so element with higher atomic masses are placed before than the elements with lower atomic masses okay so here and there some misplacements you can observe right so that is another limitation of a mineral use periodic table so you know most of the cases you you will find this kind of pairs everywhere i mean uh like every uh situation in the periodic table okay so one such example i have mentioned here actually tellurium must come here because it has a higher atomic mass but tellurium is placed first later iodine right so this kind of situations also you will find in a periodic table right so this is all about mental use periodic table okay so you must know on what basis mendeleev has given his periodic table it is it is based on atomic mass and very famous sentence you should not forget that what is that physical and chemical properties are periodic functions of their atomic masses okay and the concept of group and period is also introduced by mendeleev and that is what used later uh to introduce modern periodic table even in our modern periodic table we say there are 18 groups and seven periods right so concept of group and p red has come from mendeleev right and uh the way he left the gaps for newly discovered element is one interesting fact what modern people thought okay so and and even modern periodic table you can give place for newly introduced elements right so that's what about mendel use periodic table so this completes our uh you know history part of what is that periodic table and in the next class i will talk about the modern periodic table in a detailed way i'll be finishing modern periodic table overview as well as you know the different classifications that are there in our ncrt textbook about modern periodic table okay so let's revise the concept and do subscribe our channel to learn the concepts in the easiest way and in a detailed way and don't forget to share the videos with your friends let everybody get benefit out of this thank you so much i'll meet you up in the next class [Music]