Class 11 Chemistry: Periodic Properties and Atomic Size

[Music] hey everyone welcome to homeschool and welcome back to class 11 chemistry series we are with the third chapter that is classification of elements and their periodic properties we have completed all about the classification we discussed about dobrinos triads newlands law of octals mindless periodic table modern periodic table in detail and we learned how we have classified modern periodic table into s block p block b block and f block based on electronic configuration and also classification based on the chemical properties of elements isn't it and in my previous video i taught you a beautiful trick to identify period number and group number of an element from the periodic table so this is a very very important question that you have to concentrate for competitive exam so they give you some atomic number and they'll ask you to which group and to which period does it belong or they'll give you electronic configuration and they ask you this question so whereas to identify that i thought you a simple trick in my previous video so you can watch the video link is provided in the description if you have not yet watched and coming to today's topic i am starting with the next aspects of the chapter all about classification we have learned now we will study about periodic properties so first try to understand the meaning of the word periodic properties see here there are certain properties of an element that gets repeated in a group after some atomic numbers so such properties are called periodic properties i mean to say suppose you have lithium its atomic number is 3 so below lithium you have sodium its atomic number is lemon there are certain properties which looks similar as that of lithium and when is our sodium coming sodium is coming after some atomic numbers between lithium and sodium you have eight other elements so you have a beryllium you have boron you have carbon you have nitrogen and after some atomic number you have got an element where in that element you will see a character getting repeated you will see a physical and chemical property getting repeated which looks exactly similar to you know the above element that particular property may be similar to the above element so that's why we say all elements which come in a same group will have same property so that particular property got repeated as you go to the bottom right so and how it got repeated after certain atomic numbers so after some atomic number you have got this atomic number where in this particular element you have the same property you have a property which is common to lithium so such properties we are going to discuss and those properties we mainly call it as periodic properties and you know what these periodic properties vary in a periodic table as you go from left to to right in a periodic table uh the property the property may increase the property may decrease and when you go from top to bottom in a group there are certain properties uh you know that can increase or decrease so there is always a slight variation in these properties so we are going to discuss about such periodic properties and their variation in a periodic table okay so if i have to list out those properties it is atomic size is the first and very very important property or we can also call it as radii atomic radii radius atomic size all same okay second one is ionization enthalpy so this is another a very very important property on which the chemical properties of elements depend so actually based on these properties you know uh the chemical reactions or the physical properties depend on right so ionization enthalpy is one such very very important property that you will observe with element and third one is electro negativity electronegativity and fourth property electron gain enthalpy so this is also one such important property that you have to study about the element and there's lots of difference between electro negativity and electron gain enthalpy all that differences we will try to study in detail right and next one is electro positivity we say something called electro positivity electro positivity is nothing but metallic character and we will also talk about balancing you know so all these are periodic properties okay and and there is certain variation in the periodic table as you go from one group to another another to another you know there is a variation right so all those variations and what are the reasons for those variations everything we have to study and in this class i am going to cover everything about atomic size radii okay we will discuss what is atomic size uh what are the different types of atomic radii are there actually and ionic size we will discuss and most importantly important topic for competitive exams is iso electronic species so to identify iso electronic species i will teach you a beautiful trick so watch the video till the end definitely it will give you 100 benefit right so let's go into the topic atomic size or atomic radii let's understand the meaning of the word atomic size which is also called as atomic radii okay see we all know atom will have a nucleus at the center and it will have many many shells around this electrons are present in the shells which are present around the nucleus right so atomic radii is nothing but it is the distance between this nuclei and the last shell okay so distance between the nuclei let me write it here it's very very important to understand distance between what and what between nuclei or nucleus and last shell or we will also call it as balanced shell right so in valence shell or in last shell our valence electrons are present so it is the distance between the nucleus and the balance shell okay so instead of calling as last shell it's nice to call it as valence shell where balance electrons are present so that distance we will call it as atomic radii and this atomic radii to measure is very very difficult okay why because see extracting single atom itself is practically not possible if you want to measure this distance you need to extract one single atom from a substance or element is it possible to extract one single atom it's not possible practically right so that is the reason you know measuring this distance that is the distance between nuclei and the last shell is practically not possible that is the reason we are taking this distance with the help of several bonds okay so by you know one atom can combine with another atom and make attractions you will observe attractions between the two atoms which we will call it as bonds we have covalent bond metallic bond right ionic bond there are so many types of bonds that can be formed when one atom combines with another atom so with the help of these bonds we are trying to find out this particular distance so we have different types of bonds isn't it so we have different types of atomic radii okay so this concept is very very important and now i'm talking about different types of atomic radii okay so why we have different types of atomic radii it's because atoms can combine with one another by various types of bonding since we cannot practically extract a single atom and then measure this distance we are measuring this distance indirectly by observing the type of bonding between the two atoms okay so we have different types of atomic radii so the first one is covalent radii so this is really very very important to measure the atomic size of many elements we have considered covalent radii okay so uh let's discuss everything about covalent radii in detail second one is metallic radii and third one van der waals radii so this van der waals radii is used in case of noble gases right so van der waals radii so let's discuss all the three in detail first and foremost covalent radii see guys this covalent radii can be used when two atoms combined with each other to form a covalent bond so how is a covalent bond is formed imagine you have hydrogen molecule where i want to find out atomic size of one hydrogen so my aim is to find out atomic size of one hydrogen atom so i take the help of h2 molecule first i'll try to identify how this h2 molecules are formed you studied in your basic classes how covalent bonds are formed right it is by overlapping of atoms see this is this is a nucleus this is uh the first shell where one electron is there so this is hydrogen atom one and this is another hydrogen atom where electron is there right let me write this electron this side this is hydrogen atom to when they overlap you know this is how the atoms overlap and here your covalent bond is formed sharing of electrons takes place that itself we will call it as covalent bond okay so this is the nucleus of first hydrogen atom this is the nucleus of second hydrogen atom so this is this is what we mean by h2 molecule okay so this is one hydrogen atom another hydrogen atom they must have combined overlapped with each other something like this so sharing of electrons took place so hydrogen molecule is formed so this is the theory behind formation of covalent bond okay and once they are covalently bonded with each other once they have overlapped with each other you know what this distance the distance between uh nucleus of this hydrogen atom and nucleus of other hydrogen atom this distance we will call it as inter nuclear distance so it is called as internuclear distance covalent radii is nothing but half of this inter nuclear distance is called as covalent radii okay see if you make this distance half you know almost it can be equal to the size a radius of this atom right see anyway actually covalent radii is smaller than actual radius but then it can be considered as one of the type of atomic radii okay so half of the internuclear distance between the atoms which have covalently bonded with each other is called as covalent radii okay so let me write its definition half of this is important half of internuclear distance between atoms between atoms which are covalently bonded covalently bonded is called as covalent radii okay so when atoms overlap with each other and the internuclear distance half is called covalent radii for example you are here let me give an example h2 molecule has the internuclear distance of around you know 72 okay so what is the atomic radii atomic radii of single hydrogen atomy 72 divided by uh you know two half of the internuclear distance so how much is your answer your answer is 36 picometer right so this is how you will find this atomic radii is what type of radii it is covalent radii okay this is the inter nuclear distance in hydrogen molecule if i have to find covalent radii it is 72 by 2 it is the half of the inter nuclear distance will give you covalent radii so this is how indirectly we are trying to find the distance between the nuclei and the elasticity okay it will not be exactly similar to the actual radius but then approximate values we will get okay so this is how the size of atom was determined i mean atomic radii was determined similarly let's go for metallic radii see now let's go for second type of radii metallic radii so usually metallic radii is designated with rm okay covalent radii r v r means small r is nothing but radius okay you see here when we have uh some metals like iron copper you know silver all these are metals so these elements will have cross and cross of atoms right so between one atom and another atom there is an attraction called metallic bond okay say here this is one atom this is another atom just they have touched with each other attraction between them is metallic bond okay and the distance between the nucleus of this atom and this atom as usual we will call it as internuclear distance so metallic radii is nothing but half of that inter nuclear distance okay say let me write it here half of half of the internuclear distance nuclear distance between the atoms between the atoms which are which are bonded by metallic bond bonded by metallic bond is called as you know metallic radii so covalent bond is formed by overlapping right whereas metallic bond is formed like this they just touch with each other two atoms okay so actually speaking half of this distance will be the actual radius of one single atom right i told you covalent radii if you consider it is actually much smaller than actual radius of the atom right but here you know this metallic radii will be exactly equal to the actual radius of atom okay so uh you know depending on the type of bonding we have this radii so half of the internuclei distance the distance between the two nuclei of between the two atoms which are bonded by metallic bond you know half of that distance we call it as metallic radii okay so hope you are clear with the difference between covalent radii and metallic radii now we will go to another important type of radii van der waals radii that's a third type of radii observe carefully guys these van der waals radii we consider only for noble gases noble gases okay see for all other elements uh to talk about atomic size we consider either covalent radii or metallic radii but to talk about the size of noble gases we will always consider van der waals radii so what is this van der waals radii so imagine this is one molecule of neon okay so the best example for noble gas is neon or helium okay so this is one neon molecule and how did this neon molecule formed this is one neon atom okay this is another neon atom so which have covalently bonded with each other okay so this makes one molecule of neon one molecule of neon there is another molecule nearby this is another molecule of neon another molecule of neon okay so actually both of them uh have certain attractions between them we call those attractions as van der waals attractions so about the different attractions uh between the atoms and molecules you will study in the chapter states of matter okay so just as of now understand between this molecule and this molecule there is a weak attractive force which we will call it as van der waals attraction okay see now observe here say this is the nucleus of this atom this is the nucleus of this atom right and anyway there is a nucleus for this atom there is a nucleus for this atom but you know here the distance between the nucleus of one of the atom of one molecule and another atom of another molecule you know you you can absorb i am not talking about this distance i am not talking about this distance this is one molecule this is another separate molecule but the distance between one of the atom of this molecule and one of the atom of this molecule so this distance this distance is what we will call it as internuclear distance okay so this is our inter nuclear distance here okay right and half of this internuclear distance okay so half of this internuclear distance is called is called no van der waals radii okay r we i will write okay so rb i can write van der waals radii right so you are getting my point right so understanding a concept is very important so half of this interval so is this radii it's much greater than actual atomic radar if you consider this atom its radii is this much but van der waals radii if you consider for this it is this much see its actual radius is this much this much but van der waals area if you consider it's much bigger right so van der waals radii is always much bigger than actual atomic radii right so this is one molecule this is another molecule atom of one molecule atom of another molecule between them half of the internuclear distance is called as van der waals radii okay so we understood covalent radii metallic radii and van der waals radii okay so any one of this radii we can identify and consider it as atomic radii okay fine and now let's summarize you know a van der waals radii let me write van der waals radii is much bigger than you know metallic radii this is important for competitive exam and this is much bigger than covalent radii right covalent radii is always smaller its value is always smaller right compared to metallic radii van der waals radii value is always higher so that's why for noble gases we consider van der waals radii as atomic radii or atomic size so we always say noble gases are bigger in size okay we say noble gases are very big in size why because as their atomic radii we are actually considering van der waals radii and walls radii is actually speaking you see half of this internuclear distance i am considering as size of this atom it's actually much bigger than actual radius of an atom right so hope you are clear with three types of radii so this way we can identify the atomic radii of a particular atom in a particular element so now let us talk about how this atomic radii varies in a periodic table i mean from left to right if i go whether this property increases or decreases why and from top to bottom if i go what happens for this property as i go from element to element from top to bottom will the size of an atom increases or decreases okay so all that we will discuss now see guys everyone observe carefully here this atomic size as we move from left to to right in a periodic table our atomic size always decreases so this is surely a very very important thing actually every other properties depend on size so you need to carefully understand this concept atomic size decreases so what do you mean by this point if i take second period elements uh i have lithium beryllium boron carbon nitrogen oxygen and fluorine you forget about noble gases because in case of noble gases i told you we will consider van der waals radii whereas van der waals radii is a very much bigger type of radii right noble gases are quite larger in size we say so except that these are the elements that come in a second period so as i move from lithium to fluorine what happens is the size decreases say normally everyone thinks that as atomic number increases size will increase but no in this case it is not true you see here lithium's atomic number 3 beryllium 4 and this is 5 this is 6 this is 7 this is 8 and this is 9 atomic number is increasing gradually but atomic size decreases so why is the reason why atomic size decreases it is because the nuclear charge i'm giving you a reason this is really very important what happens here the nuclear charge increases so this is what your answer so what do you mean by nuclear charge it is the total positive charge of an atom so which particles are responsible for positive charge protons where are the protons present inside the nucleus right so let us see in case of lithium say this is the nucleus of lithium you have three protons and whereas you know outermost electrons are present in the third shell isn't it so in the outermost shell you have like one electron right see what is its electronic configuration one s two two s one so one s is first one so uh this is a nucleus this is a nucleus first station second shift so in the second shell one electron you have coming to beryllium in beryllium nucleus has four protons and the outermost shell has two electrons coming to boron in boron you have nucleus have five protons whereas outermost shell has three electrons right uh coming to carbon you know you have six protons first shell outermost shell has four electrons you see here as you go from lithium to fluorine outermost shell is your second shell only so your number of electrons are increasing as you go from lithium to fluorine but those electrons are there in a second shell shell number is not increasing all electrons are present in a second shell only i'm talking about valence electron what is increasing is nuclear charge number of protons are increasing so as number of protons increases what would happen this nucleus tries to pull the outermost shell towards itself okay imagine in carbon outermost shell is here so this shell will get pulled more towards nucleus okay so you will find more attraction between nucleus and the elasticity when when more number of protons are there inside the nucleus okay so what happens as a result of this since there is a more attraction between nucleus and last shell last shell will slightly move towards nucleus so when elasticity slightly moved towards nucleus automatically radius decreases the size decreases okay because outer most shall is same in all the elements of you know second period outermost shell is your second shell outermost shall is same but number of protons are increasing as a result attraction between the nucleus and you know outermost shell increases because of that outermost shell is pulled more and more towards nucleus as the number of protons increases okay so that way we say the size always decreases when we go from left to right in a periodic table size decreases decreases remember this why because nuclear charge increases that is the number of protons inside the nucleus is increasing fine and the next thing is next point from top to bottom what will happen from top to bottom in a periodic table that means let me take the first group lithium sodium potassium rubidium cesium so what will happen here is the size will increase okay atomic size increases this is really very important lithium's atomic number is 3 sodium's atomic number is potassium's is 90. so you would ask me here also atomic number increasing that means the number of protons inside the nucleus increases nuclear charge increases if nuclear charge increases what should happen the size must decrease right but here what is happening see lithium your outermost electron is in second shell whereas sodium your outermost electron is very third shell potassium your outermost electron is there in fourth shell see the number of shells are increasing okay so outer most shelly somewhere very far as you go from lithium to cesium right so the shell number increases so here there's no point in increasing nuclear charge even if the nuclear charge is increasing since the shell number is increasing atomic size will increase here what happened the last shell is same in all the elements protons increasing so attraction between the nucleus and last shell increases last shell will move slightly more near to the nucleus so atomic size decreased but here what's happening from top to bottom the shells shell count is increasing lithium has two shells sodium has three shells potassium has four shells and rubidium outermost electron is there in fifth shell shell most shell is increasing atomic size is after all a distance between nucleus and the last shell when the last shell is increasing it is there very very far from nucleus so automatically atomic size will increase though nuclear charge increases it doesn't matter atomic size increases because because what is the reason here because number of shells are increasing number of shells increases this is the reason guys so very very important along with the reason you must learn see from left to right in a periodic table as you go size will decrease what is the reason reason is nuclear charge increases from top to bottom in a periodic table atomic size increases what is the reason number of shells increases so this is really a very very basic point one must remember right so this is all about atomic size or atomic radii now let's talk about ionic radii see what may be the difference between atomic size and ionic size atom is neutral ion is it has some charge positive or negative charge let's understand why this ions are formed right for example right see we all know there are two types of ion one is cation the other one is anion for example i will take sodium whose atomic number is 11 if i have to write its electronic configuration 1s2 2s2 2p6 3s1 right see if it can lose this electron it will achieve noble gas electronic configuration it becomes stable so this particular sodium loses it will lose one electron and it will become n a plus so now this n a plus has electronic configuration 1 s 2 2 s 2 2 p 6 so since it has lost so why we have put positive charges because we all know our sodium right inside the nucleus it has 11 protons which are positive and outside the nucleus in different shells you have 11 electrons which are negatively charged so in sodium atom there are 11 protons with positive charge there are 11 electrons negative charge so number of positive charges were equal to the number of negative charges so what happened the atom became neutral but now what happened here sodium lost one electron now it has got only 10 electrons in variations now can i call this as a neutral atom no positive charges are more negative charges are less so this particular atom will have a positive charge so n a plus why do we write n a plus always when something on losing electron it gets positive side because i'm losing electron your proton count is more protons are positively charged since proton count is more see 11 protons 10 electrons only after losing one electron proton count is more right more positive charges are there so we put positive charge on sodium so normally we say whenever something loses electron that gets converted into cation we say so positive ion is always called as cation okay fine and similarly how do you get a negative ion see fluorine is a atomic number nine if i have to write its electronic configuration 1s22p5 see if 2p5 right yeah if it gains 1 plus 1 electron if you add it will have noble gas electronic configuration 1s2 2s2 2p6 isn't it so after gaining one electron this f is not a neutral atom now it has become f minus which we will call it as anion okay so why this negative charge say in the nucleus of fluorine you have nine protons but one extra electron has added initially there were nine electrons but now you added one electron only then it gets stability right so all together you have ten electron so negative charges are more than positive charges so as a whole this fluorine atom is becoming negatively charged so now it is no more a neutral atom it has become charged atom which we call it as ion negative charge if it is there anion we say so this is how cation and anion formation takes place okay and always remember cations cations cations are always smaller than parent atoms parent atom okay whereas anions are always bigger than parent atoms this is really very important that means if i ask you between f and f minus which one is bigger in size see f minus more electrons are there right if more electrons are there more repulsion you will observe since more repulsion is there you will not expect so much attraction from nucleus and outermost shell shell goes away and away so atomic size increases so that way we say you know always anions are greater in size than parent atom say now here between sodium and na plus which is greater in size see it has lost electron right on losing electron you got cation number of positive charges more just now i told you as the number of uh positive charges protons increases in the nucleus the last shell moves more and more towards nucleus because of more attraction between nucleus and the last shell when the last shell is pulled towards the nucleus atomic size decreases so definitely here you know n a will have greater size than n a plus so that's why i told you cations are always smaller than parent atom anions are always bigger than parent atom okay so now on this concept definitely you can expect few competitive question say for example you have i i plus and i minus i d neutral atom iodine cation iodine anion okay so among them which one is bigger or they'll ask you see the question is arrange arrange in decreasing order decreasing order of their size okay so size of ion is ionic size size of atom is atomic size whatever so you have to arrange these species in the decreasing order of their size so decreasing order means bigger size to smaller size so who is bigger here i already told you anions are bigger than parent this is parent id neutral one this is cation this is anion always i minus is greater than neutral one this is greater than i plus so this is your correct order right so this kind of questions you can expect for your competitive examination so this is how questions can be asked on ionic size you should always know anions are bigger because more electrons no more repulsion you will observe between electron shell will go outer and outer so you will not have enough attraction between nucleus and outer shell okay so shell goes away and away so size increases whereas in cations more positive charges so shell moves more towards nucleus so size automatically decreases than expected so cations are almost always smaller in size anions are always bigger in size than neutral parent atom okay so that's all about ionic size now let us talk about very very important concept iso electronic species see guys just like isotopes isobars isotones we have something called iso electronic species so iso electronic species in the sense those species it can it can be ions most of the time it can be a cations or anions okay or combination of cations are anions so those species especially it is always a charged or uncharged i cannot specifically say only charge so charged or uncharged species with the same number of electrons this is important same number of electrons is called isoelectronic species for example just observe these ions f minus o minus 2 n minus 3 mg plus 2 a l plus 3 okay so here atomic number of fluorine nine atomic number of oxygen eight atomic number of nitrogen seven atomic number of mg12 atomic number of al-13 right so what is common here atomic numbers are different but you see f minus means what one electron extra so 9 plus 1 there are 10 electrons oxygen 8 electrons were there now minus two means what two electrons extra minus anions how anions are formed always by the addition of electrons so minus one means one electron is added to neutral fluorine minus two means two electrons are added to neutral oxygen okay so oxygen neutral one already has eight electrons eight plus two ten so ten electrons nitrogen already has seven minus 3 min 7 plus 3 10 electrons so plus means what it has lost electrons from the existing one so mg neutral had 12 plus 2 means remove 2 electron if you remove 12 minus 2 if you do 10 electrons say aluminum 13 electrons it had but a l plus 3 in a l plus 3 you will have 10 electrons plus means what losing electron okay see all of them have 10 electrons so those species with the same number of electrons are called iso electronic species so all these i can say iso electronic species so what are isoelectronic species different elements or different ions different atomic number but same number of electrons are electronic species so you must completely understand the concept what actually we mean by isoelectronic species and after this you have to decide which ion has more size or less size okay among isoelectronic species you can't just decide based on atomic number see actually uh fluorine oxygen and mg and aluminium comes in the third period and these are coming in the second period and they don't belong to a same group right so how would you judge the size here always remember in case of iso electronic species okay so in iso electronic species species okay as a nuclear charge increases as nuclear charge increases so when does the nuclear charge increases atomic number increases okay so as nuclear charge increases that means as atomic number increases atomic number increases size decreases size decreases we know whenever nuclear charge increases what would happen attraction between outermost shell and nucleus will increase as a result of that outermost shell will move more and more near to the nucleus so that way size decreases so here when does the nuclear charge can increase atomic number increases so just think of connect size and atomic number in case of isoelectronic species only you can't apply this for neutral elements or whatever it is when they are having same number of electron among them if you have to decide who is more in size who is less in size then you can apply this so this is what your trick to identify the size in isoelectronic species more the atomic number lesser is the size so now can you decide who is lesser in size which one has less ionic size or atomic size it is just check the atomic number maximum atomic number is for a l plus 3 so a l plus 3 is least in atomic size that mg plus 2 next smaller one is you know this one f minus next least size is o minus 2 then the highest size ionic size you will find for n minus 3 so n minus 3 is bigger ion a l plus 3 is smaller ion in these iso electronic species okay so this is how you have to identify which ion is bigger which is smaller as long as they are isoelectronic species okay so this this trick can help you out in solving many questions almost all the questions relating to isoelectronic species so what is important is first you should know the definition of isoelectronic species then you must able to identify whether the given things are isoelectronic species or not then if any question is asked based on the size they will ask you arrange them in the increasing order of their size or decreasing order of their size so then size related things if you want to answer just remember more the atomic number lesser is the size more the atomic number lesser is the size of iso electronic species okay so this is really very very important right okay so that's all about today's video and in my next class i will come up with one more important periodic property that is ionization enthalpy till then revise the concept take care and do subscribe our channel to learn the concepts in easiest way and in a detailed way thank you so much [Music]

[Music] hey everyone welcome to homeschool and welcome back to class 11 chemistry series we are with the third chapter that is classification of elements and their periodic properties we have completed all about the classification we discussed about dobrinos triads newlands law of octals mindless periodic table modern periodic table in detail and we learned how we have classified modern periodic table into s block p block b block and f block based on electronic configuration and also classification based on the chemical properties of elements isn&#39;t it and in my previous video i taught you a beautiful trick to identify period number and group number of an element from the periodic table so this is a very very important question that you have to concentrate for competitive exam so they give you some atomic number and they&#39;ll ask you to which group and to which period does it belong or they&#39;ll give you electronic configuration and they ask you this question so whereas to identify that i thought you a simple trick in my previous video so you can watch the video link is provided in the description if you have not yet watched and coming to today&#39;s topic i am starting with the next aspects of the chapter all about classification we have learned now we will study about periodic properties so first try to understand the meaning of the word periodic properties see here there are certain properties of an element that gets repeated in a group after some atomic numbers so such properties are called periodic properties i mean to say suppose you have lithium its atomic number is 3 so below lithium you have sodium its atomic number is lemon there are certain properties which looks similar as that of lithium and when is our sodium coming sodium is coming after some atomic numbers between lithium and sodium you have eight other elements so you have a beryllium you have boron you have carbon you have nitrogen and after some atomic number you have got an element where in that element you will see a character getting repeated you will see a physical and chemical property getting repeated which looks exactly similar to you know the above element that particular property may be similar to the above element so that&#39;s why we say all elements which come in a same group will have same property so that particular property got repeated as you go to the bottom right so and how it got repeated after certain atomic numbers so after some atomic number you have got this atomic number where in this particular element you have the same property you have a property which is common to lithium so such properties we are going to discuss and those properties we mainly call it as periodic properties and you know what these periodic properties vary in a periodic table as you go from left to to right in a periodic table uh the property the property may increase the property may decrease and when you go from top to bottom in a group there are certain properties uh you know that can increase or decrease so there is always a slight variation in these properties so we are going to discuss about such periodic properties and their variation in a periodic table okay so if i have to list out those properties it is atomic size is the first and very very important property or we can also call it as radii atomic radii radius atomic size all same okay second one is ionization enthalpy so this is another a very very important property on which the chemical properties of elements depend so actually based on these properties you know uh the chemical reactions or the physical properties depend on right so ionization enthalpy is one such very very important property that you will observe with element and third one is electro negativity electronegativity and fourth property electron gain enthalpy so this is also one such important property that you have to study about the element and there&#39;s lots of difference between electro negativity and electron gain enthalpy all that differences we will try to study in detail right and next one is electro positivity we say something called electro positivity electro positivity is nothing but metallic character and we will also talk about balancing you know so all these are periodic properties okay and and there is certain variation in the periodic table as you go from one group to another another to another you know there is a variation right so all those variations and what are the reasons for those variations everything we have to study and in this class i am going to cover everything about atomic size radii okay we will discuss what is atomic size uh what are the different types of atomic radii are there actually and ionic size we will discuss and most importantly important topic for competitive exams is iso electronic species so to identify iso electronic species i will teach you a beautiful trick so watch the video till the end definitely it will give you 100 benefit right so let&#39;s go into the topic atomic size or atomic radii let&#39;s understand the meaning of the word atomic size which is also called as atomic radii okay see we all know atom will have a nucleus at the center and it will have many many shells around this electrons are present in the shells which are present around the nucleus right so atomic radii is nothing but it is the distance between this nuclei and the last shell okay so distance between the nuclei let me write it here it&#39;s very very important to understand distance between what and what between nuclei or nucleus and last shell or we will also call it as balanced shell right so in valence shell or in last shell our valence electrons are present so it is the distance between the nucleus and the balance shell okay so instead of calling as last shell it&#39;s nice to call it as valence shell where balance electrons are present so that distance we will call it as atomic radii and this atomic radii to measure is very very difficult okay why because see extracting single atom itself is practically not possible if you want to measure this distance you need to extract one single atom from a substance or element is it possible to extract one single atom it&#39;s not possible practically right so that is the reason you know measuring this distance that is the distance between nuclei and the last shell is practically not possible that is the reason we are taking this distance with the help of several bonds okay so by you know one atom can combine with another atom and make attractions you will observe attractions between the two atoms which we will call it as bonds we have covalent bond metallic bond right ionic bond there are so many types of bonds that can be formed when one atom combines with another atom so with the help of these bonds we are trying to find out this particular distance so we have different types of bonds isn&#39;t it so we have different types of atomic radii okay so this concept is very very important and now i&#39;m talking about different types of atomic radii okay so why we have different types of atomic radii it&#39;s because atoms can combine with one another by various types of bonding since we cannot practically extract a single atom and then measure this distance we are measuring this distance indirectly by observing the type of bonding between the two atoms okay so we have different types of atomic radii so the first one is covalent radii so this is really very very important to measure the atomic size of many elements we have considered covalent radii okay so uh let&#39;s discuss everything about covalent radii in detail second one is metallic radii and third one van der waals radii so this van der waals radii is used in case of noble gases right so van der waals radii so let&#39;s discuss all the three in detail first and foremost covalent radii see guys this covalent radii can be used when two atoms combined with each other to form a covalent bond so how is a covalent bond is formed imagine you have hydrogen molecule where i want to find out atomic size of one hydrogen so my aim is to find out atomic size of one hydrogen atom so i take the help of h2 molecule first i&#39;ll try to identify how this h2 molecules are formed you studied in your basic classes how covalent bonds are formed right it is by overlapping of atoms see this is this is a nucleus this is uh the first shell where one electron is there so this is hydrogen atom one and this is another hydrogen atom where electron is there right let me write this electron this side this is hydrogen atom to when they overlap you know this is how the atoms overlap and here your covalent bond is formed sharing of electrons takes place that itself we will call it as covalent bond okay so this is the nucleus of first hydrogen atom this is the nucleus of second hydrogen atom so this is this is what we mean by h2 molecule okay so this is one hydrogen atom another hydrogen atom they must have combined overlapped with each other something like this so sharing of electrons took place so hydrogen molecule is formed so this is the theory behind formation of covalent bond okay and once they are covalently bonded with each other once they have overlapped with each other you know what this distance the distance between uh nucleus of this hydrogen atom and nucleus of other hydrogen atom this distance we will call it as inter nuclear distance so it is called as internuclear distance covalent radii is nothing but half of this inter nuclear distance is called as covalent radii okay see if you make this distance half you know almost it can be equal to the size a radius of this atom right see anyway actually covalent radii is smaller than actual radius but then it can be considered as one of the type of atomic radii okay so half of the internuclear distance between the atoms which have covalently bonded with each other is called as covalent radii okay so let me write its definition half of this is important half of internuclear distance between atoms between atoms which are covalently bonded covalently bonded is called as covalent radii okay so when atoms overlap with each other and the internuclear distance half is called covalent radii for example you are here let me give an example h2 molecule has the internuclear distance of around you know 72 okay so what is the atomic radii atomic radii of single hydrogen atomy 72 divided by uh you know two half of the internuclear distance so how much is your answer your answer is 36 picometer right so this is how you will find this atomic radii is what type of radii it is covalent radii okay this is the inter nuclear distance in hydrogen molecule if i have to find covalent radii it is 72 by 2 it is the half of the inter nuclear distance will give you covalent radii so this is how indirectly we are trying to find the distance between the nuclei and the elasticity okay it will not be exactly similar to the actual radius but then approximate values we will get okay so this is how the size of atom was determined i mean atomic radii was determined similarly let&#39;s go for metallic radii see now let&#39;s go for second type of radii metallic radii so usually metallic radii is designated with rm okay covalent radii r v r means small r is nothing but radius okay you see here when we have uh some metals like iron copper you know silver all these are metals so these elements will have cross and cross of atoms right so between one atom and another atom there is an attraction called metallic bond okay say here this is one atom this is another atom just they have touched with each other attraction between them is metallic bond okay and the distance between the nucleus of this atom and this atom as usual we will call it as internuclear distance so metallic radii is nothing but half of that inter nuclear distance okay say let me write it here half of half of the internuclear distance nuclear distance between the atoms between the atoms which are which are bonded by metallic bond bonded by metallic bond is called as you know metallic radii so covalent bond is formed by overlapping right whereas metallic bond is formed like this they just touch with each other two atoms okay so actually speaking half of this distance will be the actual radius of one single atom right i told you covalent radii if you consider it is actually much smaller than actual radius of the atom right but here you know this metallic radii will be exactly equal to the actual radius of atom okay so uh you know depending on the type of bonding we have this radii so half of the internuclei distance the distance between the two nuclei of between the two atoms which are bonded by metallic bond you know half of that distance we call it as metallic radii okay so hope you are clear with the difference between covalent radii and metallic radii now we will go to another important type of radii van der waals radii that&#39;s a third type of radii observe carefully guys these van der waals radii we consider only for noble gases noble gases okay see for all other elements uh to talk about atomic size we consider either covalent radii or metallic radii but to talk about the size of noble gases we will always consider van der waals radii so what is this van der waals radii so imagine this is one molecule of neon okay so the best example for noble gas is neon or helium okay so this is one neon molecule and how did this neon molecule formed this is one neon atom okay this is another neon atom so which have covalently bonded with each other okay so this makes one molecule of neon one molecule of neon there is another molecule nearby this is another molecule of neon another molecule of neon okay so actually both of them uh have certain attractions between them we call those attractions as van der waals attractions so about the different attractions uh between the atoms and molecules you will study in the chapter states of matter okay so just as of now understand between this molecule and this molecule there is a weak attractive force which we will call it as van der waals attraction okay see now observe here say this is the nucleus of this atom this is the nucleus of this atom right and anyway there is a nucleus for this atom there is a nucleus for this atom but you know here the distance between the nucleus of one of the atom of one molecule and another atom of another molecule you know you you can absorb i am not talking about this distance i am not talking about this distance this is one molecule this is another separate molecule but the distance between one of the atom of this molecule and one of the atom of this molecule so this distance this distance is what we will call it as internuclear distance okay so this is our inter nuclear distance here okay right and half of this internuclear distance okay so half of this internuclear distance is called is called no van der waals radii okay r we i will write okay so rb i can write van der waals radii right so you are getting my point right so understanding a concept is very important so half of this interval so is this radii it&#39;s much greater than actual atomic radar if you consider this atom its radii is this much but van der waals radii if you consider for this it is this much see its actual radius is this much this much but van der waals area if you consider it&#39;s much bigger right so van der waals radii is always much bigger than actual atomic radii right so this is one molecule this is another molecule atom of one molecule atom of another molecule between them half of the internuclear distance is called as van der waals radii okay so we understood covalent radii metallic radii and van der waals radii okay so any one of this radii we can identify and consider it as atomic radii okay fine and now let&#39;s summarize you know a van der waals radii let me write van der waals radii is much bigger than you know metallic radii this is important for competitive exam and this is much bigger than covalent radii right covalent radii is always smaller its value is always smaller right compared to metallic radii van der waals radii value is always higher so that&#39;s why for noble gases we consider van der waals radii as atomic radii or atomic size so we always say noble gases are bigger in size okay we say noble gases are very big in size why because as their atomic radii we are actually considering van der waals radii and walls radii is actually speaking you see half of this internuclear distance i am considering as size of this atom it&#39;s actually much bigger than actual radius of an atom right so hope you are clear with three types of radii so this way we can identify the atomic radii of a particular atom in a particular element so now let us talk about how this atomic radii varies in a periodic table i mean from left to right if i go whether this property increases or decreases why and from top to bottom if i go what happens for this property as i go from element to element from top to bottom will the size of an atom increases or decreases okay so all that we will discuss now see guys everyone observe carefully here this atomic size as we move from left to to right in a periodic table our atomic size always decreases so this is surely a very very important thing actually every other properties depend on size so you need to carefully understand this concept atomic size decreases so what do you mean by this point if i take second period elements uh i have lithium beryllium boron carbon nitrogen oxygen and fluorine you forget about noble gases because in case of noble gases i told you we will consider van der waals radii whereas van der waals radii is a very much bigger type of radii right noble gases are quite larger in size we say so except that these are the elements that come in a second period so as i move from lithium to fluorine what happens is the size decreases say normally everyone thinks that as atomic number increases size will increase but no in this case it is not true you see here lithium&#39;s atomic number 3 beryllium 4 and this is 5 this is 6 this is 7 this is 8 and this is 9 atomic number is increasing gradually but atomic size decreases so why is the reason why atomic size decreases it is because the nuclear charge i&#39;m giving you a reason this is really very important what happens here the nuclear charge increases so this is what your answer so what do you mean by nuclear charge it is the total positive charge of an atom so which particles are responsible for positive charge protons where are the protons present inside the nucleus right so let us see in case of lithium say this is the nucleus of lithium you have three protons and whereas you know outermost electrons are present in the third shell isn&#39;t it so in the outermost shell you have like one electron right see what is its electronic configuration one s two two s one so one s is first one so uh this is a nucleus this is a nucleus first station second shift so in the second shell one electron you have coming to beryllium in beryllium nucleus has four protons and the outermost shell has two electrons coming to boron in boron you have nucleus have five protons whereas outermost shell has three electrons right uh coming to carbon you know you have six protons first shell outermost shell has four electrons you see here as you go from lithium to fluorine outermost shell is your second shell only so your number of electrons are increasing as you go from lithium to fluorine but those electrons are there in a second shell shell number is not increasing all electrons are present in a second shell only i&#39;m talking about valence electron what is increasing is nuclear charge number of protons are increasing so as number of protons increases what would happen this nucleus tries to pull the outermost shell towards itself okay imagine in carbon outermost shell is here so this shell will get pulled more towards nucleus okay so you will find more attraction between nucleus and the elasticity when when more number of protons are there inside the nucleus okay so what happens as a result of this since there is a more attraction between nucleus and last shell last shell will slightly move towards nucleus so when elasticity slightly moved towards nucleus automatically radius decreases the size decreases okay because outer most shall is same in all the elements of you know second period outermost shell is your second shell outermost shall is same but number of protons are increasing as a result attraction between the nucleus and you know outermost shell increases because of that outermost shell is pulled more and more towards nucleus as the number of protons increases okay so that way we say the size always decreases when we go from left to right in a periodic table size decreases decreases remember this why because nuclear charge increases that is the number of protons inside the nucleus is increasing fine and the next thing is next point from top to bottom what will happen from top to bottom in a periodic table that means let me take the first group lithium sodium potassium rubidium cesium so what will happen here is the size will increase okay atomic size increases this is really very important lithium&#39;s atomic number is 3 sodium&#39;s atomic number is potassium&#39;s is 90. so you would ask me here also atomic number increasing that means the number of protons inside the nucleus increases nuclear charge increases if nuclear charge increases what should happen the size must decrease right but here what is happening see lithium your outermost electron is in second shell whereas sodium your outermost electron is very third shell potassium your outermost electron is there in fourth shell see the number of shells are increasing okay so outer most shelly somewhere very far as you go from lithium to cesium right so the shell number increases so here there&#39;s no point in increasing nuclear charge even if the nuclear charge is increasing since the shell number is increasing atomic size will increase here what happened the last shell is same in all the elements protons increasing so attraction between the nucleus and last shell increases last shell will move slightly more near to the nucleus so atomic size decreased but here what&#39;s happening from top to bottom the shells shell count is increasing lithium has two shells sodium has three shells potassium has four shells and rubidium outermost electron is there in fifth shell shell most shell is increasing atomic size is after all a distance between nucleus and the last shell when the last shell is increasing it is there very very far from nucleus so automatically atomic size will increase though nuclear charge increases it doesn&#39;t matter atomic size increases because because what is the reason here because number of shells are increasing number of shells increases this is the reason guys so very very important along with the reason you must learn see from left to right in a periodic table as you go size will decrease what is the reason reason is nuclear charge increases from top to bottom in a periodic table atomic size increases what is the reason number of shells increases so this is really a very very basic point one must remember right so this is all about atomic size or atomic radii now let&#39;s talk about ionic radii see what may be the difference between atomic size and ionic size atom is neutral ion is it has some charge positive or negative charge let&#39;s understand why this ions are formed right for example right see we all know there are two types of ion one is cation the other one is anion for example i will take sodium whose atomic number is 11 if i have to write its electronic configuration 1s2 2s2 2p6 3s1 right see if it can lose this electron it will achieve noble gas electronic configuration it becomes stable so this particular sodium loses it will lose one electron and it will become n a plus so now this n a plus has electronic configuration 1 s 2 2 s 2 2 p 6 so since it has lost so why we have put positive charges because we all know our sodium right inside the nucleus it has 11 protons which are positive and outside the nucleus in different shells you have 11 electrons which are negatively charged so in sodium atom there are 11 protons with positive charge there are 11 electrons negative charge so number of positive charges were equal to the number of negative charges so what happened the atom became neutral but now what happened here sodium lost one electron now it has got only 10 electrons in variations now can i call this as a neutral atom no positive charges are more negative charges are less so this particular atom will have a positive charge so n a plus why do we write n a plus always when something on losing electron it gets positive side because i&#39;m losing electron your proton count is more protons are positively charged since proton count is more see 11 protons 10 electrons only after losing one electron proton count is more right more positive charges are there so we put positive charge on sodium so normally we say whenever something loses electron that gets converted into cation we say so positive ion is always called as cation okay fine and similarly how do you get a negative ion see fluorine is a atomic number nine if i have to write its electronic configuration 1s22p5 see if 2p5 right yeah if it gains 1 plus 1 electron if you add it will have noble gas electronic configuration 1s2 2s2 2p6 isn&#39;t it so after gaining one electron this f is not a neutral atom now it has become f minus which we will call it as anion okay so why this negative charge say in the nucleus of fluorine you have nine protons but one extra electron has added initially there were nine electrons but now you added one electron only then it gets stability right so all together you have ten electron so negative charges are more than positive charges so as a whole this fluorine atom is becoming negatively charged so now it is no more a neutral atom it has become charged atom which we call it as ion negative charge if it is there anion we say so this is how cation and anion formation takes place okay and always remember cations cations cations are always smaller than parent atoms parent atom okay whereas anions are always bigger than parent atoms this is really very important that means if i ask you between f and f minus which one is bigger in size see f minus more electrons are there right if more electrons are there more repulsion you will observe since more repulsion is there you will not expect so much attraction from nucleus and outermost shell shell goes away and away so atomic size increases so that way we say you know always anions are greater in size than parent atom say now here between sodium and na plus which is greater in size see it has lost electron right on losing electron you got cation number of positive charges more just now i told you as the number of uh positive charges protons increases in the nucleus the last shell moves more and more towards nucleus because of more attraction between nucleus and the last shell when the last shell is pulled towards the nucleus atomic size decreases so definitely here you know n a will have greater size than n a plus so that&#39;s why i told you cations are always smaller than parent atom anions are always bigger than parent atom okay so now on this concept definitely you can expect few competitive question say for example you have i i plus and i minus i d neutral atom iodine cation iodine anion okay so among them which one is bigger or they&#39;ll ask you see the question is arrange arrange in decreasing order decreasing order of their size okay so size of ion is ionic size size of atom is atomic size whatever so you have to arrange these species in the decreasing order of their size so decreasing order means bigger size to smaller size so who is bigger here i already told you anions are bigger than parent this is parent id neutral one this is cation this is anion always i minus is greater than neutral one this is greater than i plus so this is your correct order right so this kind of questions you can expect for your competitive examination so this is how questions can be asked on ionic size you should always know anions are bigger because more electrons no more repulsion you will observe between electron shell will go outer and outer so you will not have enough attraction between nucleus and outer shell okay so shell goes away and away so size increases whereas in cations more positive charges so shell moves more towards nucleus so size automatically decreases than expected so cations are almost always smaller in size anions are always bigger in size than neutral parent atom okay so that&#39;s all about ionic size now let us talk about very very important concept iso electronic species see guys just like isotopes isobars isotones we have something called iso electronic species so iso electronic species in the sense those species it can it can be ions most of the time it can be a cations or anions okay or combination of cations are anions so those species especially it is always a charged or uncharged i cannot specifically say only charge so charged or uncharged species with the same number of electrons this is important same number of electrons is called isoelectronic species for example just observe these ions f minus o minus 2 n minus 3 mg plus 2 a l plus 3 okay so here atomic number of fluorine nine atomic number of oxygen eight atomic number of nitrogen seven atomic number of mg12 atomic number of al-13 right so what is common here atomic numbers are different but you see f minus means what one electron extra so 9 plus 1 there are 10 electrons oxygen 8 electrons were there now minus two means what two electrons extra minus anions how anions are formed always by the addition of electrons so minus one means one electron is added to neutral fluorine minus two means two electrons are added to neutral oxygen okay so oxygen neutral one already has eight electrons eight plus two ten so ten electrons nitrogen already has seven minus 3 min 7 plus 3 10 electrons so plus means what it has lost electrons from the existing one so mg neutral had 12 plus 2 means remove 2 electron if you remove 12 minus 2 if you do 10 electrons say aluminum 13 electrons it had but a l plus 3 in a l plus 3 you will have 10 electrons plus means what losing electron okay see all of them have 10 electrons so those species with the same number of electrons are called iso electronic species so all these i can say iso electronic species so what are isoelectronic species different elements or different ions different atomic number but same number of electrons are electronic species so you must completely understand the concept what actually we mean by isoelectronic species and after this you have to decide which ion has more size or less size okay among isoelectronic species you can&#39;t just decide based on atomic number see actually uh fluorine oxygen and mg and aluminium comes in the third period and these are coming in the second period and they don&#39;t belong to a same group right so how would you judge the size here always remember in case of iso electronic species okay so in iso electronic species species okay as a nuclear charge increases as nuclear charge increases so when does the nuclear charge increases atomic number increases okay so as nuclear charge increases that means as atomic number increases atomic number increases size decreases size decreases we know whenever nuclear charge increases what would happen attraction between outermost shell and nucleus will increase as a result of that outermost shell will move more and more near to the nucleus so that way size decreases so here when does the nuclear charge can increase atomic number increases so just think of connect size and atomic number in case of isoelectronic species only you can&#39;t apply this for neutral elements or whatever it is when they are having same number of electron among them if you have to decide who is more in size who is less in size then you can apply this so this is what your trick to identify the size in isoelectronic species more the atomic number lesser is the size so now can you decide who is lesser in size which one has less ionic size or atomic size it is just check the atomic number maximum atomic number is for a l plus 3 so a l plus 3 is least in atomic size that mg plus 2 next smaller one is you know this one f minus next least size is o minus 2 then the highest size ionic size you will find for n minus 3 so n minus 3 is bigger ion a l plus 3 is smaller ion in these iso electronic species okay so this is how you have to identify which ion is bigger which is smaller as long as they are isoelectronic species okay so this this trick can help you out in solving many questions almost all the questions relating to isoelectronic species so what is important is first you should know the definition of isoelectronic species then you must able to identify whether the given things are isoelectronic species or not then if any question is asked based on the size they will ask you arrange them in the increasing order of their size or decreasing order of their size so then size related things if you want to answer just remember more the atomic number lesser is the size more the atomic number lesser is the size of iso electronic species okay so this is really very very important right okay so that&#39;s all about today&#39;s video and in my next class i will come up with one more important periodic property that is ionization enthalpy till then revise the concept take care and do subscribe our channel to learn the concepts in easiest way and in a detailed way thank you so much [Music]

Transcript for:Class 11 Chemistry: Periodic Properties and Atomic Size

Transcript for:
Class 11 Chemistry: Periodic Properties and Atomic Size