hello my shimmering Stars today I shot a Grover welcome you all to this amazing platform of PW English so students I welcome you all to your Nexus batch and today we are going to start with our lecture number two based upon your chapter chemical bonding so students in your class 11th till now we have covered periodic classification and the periodic properties and we have initially started the chapter chemical bonding in the previous session we took a you know General introduction with regard to the modes of chemical bonding that how do chemical bond you know formation occurs or I would say that basically there were two steps we thought over there the initial one was by sharing of electrons the another one was by transferring of electrons so we started these two concepts in detail with some examples now we are going to move you know forward with a new topic in our session today that is going to be Lewis Dot representation Lewis Theory and it is very very interesting also students we are going to calculate the formal charge on the particular atom so how to do that ma'am and how we are going to proceed so let us start this with a beautiful smile so students as I've already told you this is going to be our lecture number two for today's class so what are the topics or what is the today's Target that we have to complete so the very first thing that you need to do over here is initially we will be understanding about Lewis Theory okay or Lewis Dot Theory you can say then we will be understanding about Lewis Dot Structure [Music] for the students we shall be understanding about the formal charge and at last we also will be reading from the ncrt highlight so you very well know with regard to inorganic I have already told you in all your classes that ncrt highlight is really very important now what is ncrt highlight if you're new to this session today or if you're new to your Nexus batch let me tell you students in ncrt highlight I just bring out the important key points from the ncrt itself so that if you're not reading ncrt if you're not going through the ncrt you can cover it over here in the session only there is no need to even read ncrt again if you are doing ncert highlights from here because we are taking important key Concepts important key points ncrt in text question ncrt back exercises over here itself yes everyone so now starting with the very first topic I'm introducing you again with your friends barium and calcium so calcium is saying hello my shimmering stars have you revised yesterday's session while barium says that hi friends be ready for this new chat after be ready for this new topic today so they are welcoming you again in your Nexus bat students yes okay so now starting with the very first part of ours that is Lewis Dot Structure okay so now one by one we will be understanding about in detail first of all let us see Lewis Theory or Lewis Dot Theory basically is used for covalent compounds it is used to represent them that how do they look alike what are the structures how do you represent covalent compounds so for that we are going to use the Lewis Dot Theory now how to draw Lewis Dot Structure this is the initial topic that will lead further on to the octat rule what are the limitations of the octet rule but before that we need to understand about Lewis Dot Structure now what it is exactly ma'am how you have to calculate it Mom Lewis Dot representational Lewis Dot Structure is something for example you have a single element or a single atom let us consider we have hydrogen how you are going to represent that hydrogen with the help of dots the dots word over here represent the valence electrons whatever the valence electrons now valence electrons are those electrons which are found in the outermost shell what are valence electrons those electrons which are found in the outermost shell so valence electrons basically are used in the formation of the covalent compounds are used in the formation of bond so see valence electron in the formation of molecule only the outer shell electron take part in chemical bond and they are known as valence electrons valence electrons let us take a general example of sodium sodium has an atomic number 11. now you very well know the electronic configuration it is going to be mam one is to 2s2 2p6 3s1 yes so what is the outermost shell let us draw this let us draw this this is your nucleus this is your first shell second shell third shell see here you can clearly observe it is your first shell second shell third shell first shell contains two electrons second shall contain two plus six eight electrons so one two three four five six seven eight and third shall contain only one electron so what a valid shell over here valid shell are those electrons which are present in the outermost shell or the shell which is the last shell so over here you can see that there is one electron in the outermost shell in the outermost shell so valence electrons valence electrons in the case of sodium comes out to be how much one electron Mark clear very easy let us take some more examples now let us this is I am calculating the number of valence electrons let us take an example of carbon carbon also let us take one more example of nitrogen thank you see nitrogen basically has an atomic number seven students so what is going to be the electronic configuration mameters 1 is 2 2s2 2p3 count electrons two plus two four four plus three is seven right now we have to represent it so it is going to be this is going to be nucleus your first shell and your second shell yeah only two shells are there now see first shell contains how many electrons over here my only two electrons only two electrons second shall contain two plus three that is five electrons so one two three four and five so outermost shell is second shell and it contains five electrons so what is going to be the valence electrons over here Phi what are the valence electrons five let us take case of carbon now carbon has an atomic number six students so you have to write the configuration one is two two s two two P two yes 2 plus 2 plus 2 that comes out to be 6 node two P two now let's draw this this is your nucleus first shell second shell first shell contains how many electrons students remember two electrons second shall contain how many electron two plus two four electrons so it is only one two three and four that means outermost shell over here contains four electrons so this is going to be your valence electrons now you very well know what are valence electrons yes okay let us take one more question then I guess valence electrons concept is quite clear to you so one more key concept of oxygen atom oxygen atom is an atomic number eight right what is going to be the configuration one is two 2s 2 now 2p 4 2 plus 2 plus 4 comes out to be eight no so if I have to make the structure nucleus first shell second shell see count the electrons now how many in partial mam two how many in second shell two plus four that means six electrons so one two three four five six that means outermost shell contains six electrons so Mom this is your valence electrons these are your valence electrons now I guess you very well know what are valence electrons yes everyone yes everyone please write it down so that I can now move on to the next part [Music] everybody write it down so that I can now move on to the next part shall we move on to the next part everybody if it is written [Music] dance to dance [Music] I have just separated it so that you can't you know mix it all together done everybody so these was all about valence electrons the calculation of [Music] valence electrons [Music] clear everyone now see students the next important key concept causal and Lewis approach chemical bonding or in other words or in other words is Lewis Theory or Lewis Dot Theory or in other words is Lewis Theory or Lewis Dot Theory let us understand this Lewis octat Rule now what is octat octat basically refers to eight electrons what is octat octat basically refers to eight electrons in some of the cases you will see duplet duplet basically is two electrons I'm mentioning it also over here if you don't know duplet basically is two electrons foreign basically is two electrons and let us sorry doctored also over here so that you can write each and every key concept octet basically is how many electrons ma'am eight electrons how many electrons eight electrons right now come back to this causal and Lewis approach chemical bonding what does it states that it states that Lewis octat rule every atom has a tendency to attain noble gas electronic configuration what are the noble gases what are the noble gases group number which group number 18 which group group number 18 yeah so each and every element you know students in the complete periodic table what it want it it wants to be stable it wants to attain the electronic configuration right so for maximum stability in order to attain it it is going to acquire which configuration the configuration which group number 18 elements hold clear now see that means to have eight valence electrons so Lewis octet rule octet here refers to eight electrons so each and every element will have a tendency to acquire eight electrons in its outermost valence shell now values shall you very well know and this is the theory which is given by the Lewis and causal approach chemical bonding so Lewis and castle Yeah so now everybody have you written this I'm getting a side see each and every key concept concept I'm mentioning over here you have to mention it in your notebooks also in your books also you have to write down moving on to the next part students now rules to write down the Lewis Dot Structure what are the rules to write down the Lewis Dot Structure very interesting segment a very important segment let us start with the very first rule very first rule is calculate the total number of valence electrons available for bonding in the given molecule okay now uh let us calculate some of the examples by doing each and every one of that so calculation of valence electrons we are starting with this part now this in molecules now only we have calculated the valence electrons in some of the cases though but over here students I am going to calculate the valence electrons in the case of molecule so let us see first of all one by one we are going to calculate so I am starting with let us write ABC that will be much better now so the first part that we are going to start with is H2 for the case of H2 molecules how you have to calculate uh that is C how many hydrogen two so here calculate total [Music] valence electrons total valence electrons how many hydrogen I'm two so two into now 2 into valence electrons of single hydrogen because there are two hydrogen right now 2 into what is the valence uh you know valence electrons of in the case of hydrogen C students hydrogen has atomic number one so electronic configuration one is one that means one electron is seen in the outermost shell so valence electron in the case of hydrogen is only one yeah so two into one comes out to be two that means two electrons are the total valence electrons that are seen in the case of H2 that are seen in which case students that are seen in the case of H2 clear everyone everyone write all of these over here one by one we are going to move on to the uh you know more examples just keep on writing these [Music] [Music] just keep on writing this now taking another example just taking another example that is option that is part B let us take in case of CH4 molecule now in the case of CH4 molecule just C total valence electrons is equivalent to what how many electrons how many carbon one so one into carbon valence electrons plus four into hydrogen valence electron how many valence electron are seen in the case of carbon now only we have calculated it over here how many electrons were seen in the case of carbon Man four valence electrons how many four plus 4 into how many valence electrons in the case of hydrogen one so this comes out to be one into four is four plus four into one is four that means total eight valence electrons are seen over here that means total eight valence electrons are seen over here for everyone [Music] write it down students this we are calculating the total valence electrons this we are calculating the total valence electrons over here calculation of valence electrons let us take more cases now shall we okay now see students here I am explaining a case which carries a negative charge let us take a case of NO3 negative No 3 negative or No 3 minus 1 it would be written now see total valence electrons or total electrons I have total valence electrons I am talking about it is equivalent to how many uh electrons are seen in the case of nitrogen now only we have calculated five valence electrons five Plus for oxygen how many uh it will be for oxygen it will be six [Music] for oxygen we have not calculated I will calculate it over here only [Music] calculating for oxygen atom okay oxygen atom has an atomic number eight so it is one is two two s two two P four four plus four eight I don't know I guess I we have done yeah we have done for oxygen sorry six electrons no so I am just clearing it out [Music] yeah six electrons now how many oxygen mam three oxygen minus 1 is written so you have to write Plus 1. if it is written minus 1 always remember if it is written minus 1 that means you have to do plus if it is written plus 1 you have to do minus clear now see so this comes out to be 5 plus 18 plus 1 that means it is 24 electrons how many valence electrons 24 valence electrons clear everybody first of all write this down let us take one more case now [Music] [Music] yeah let us take another case D part nh4 positive so total valence electrons [Music] is equivalent to for the case of nitrogen how many total valence electrons were there num five one nitrogen so one into five plus for hydrogen how many valence electrons one total hydrogen four one into four now it is written plus one so we are going to subtract it you are going to do what you are going to subtract it so what it will be 5 plus 4 minus 1 that means how many electrons eight electrons clear everyone everybody please write it down I am doing from very basic key concept students I am taking very basic key concept clear [Music] everyone [Music] yeah so this was all about the calculation of valence electrons among all of these so we have calculated valence electrons the very first rule was calculate the total number of valence electrons available for bonding in a given molecule now for an iron that means which carries a negative charge add electrons equal to the charge in the valence electrons of an atom for an ion that means the one which carries a negative charge you have to add it when there is a positive charge you have to subtract it that means for cation remove the electrons clear everybody and then example they have given you for the case of nh4 positive now only we have calculated C for the case of nh4 positive it comes out to be how many mam eight electrons how many mam eight electrons yes everybody please write it down students that's great moving on to the next part students next rule to write down the Lewis Dot Structure basically is what see least electronegative polyvalent atom occupies the central position now see what happens let us take a case of [Music] nf3 okay now how do you know which atom is going to acquire the central most position okay now many of you may write it as nitrogen fluorine fluorine fluorine many of you may also write it as fluorine fluorine fluorine nitrogen which of the following structure is right one how do you know that Mom how we can know that which of the following structure is the correct one let me tell you this structure is going to be the correct one and this structure is going to be the incorrect one but what is the reason ma'am what is the reason reason is least electronegative polyvalent atom will acquire the central most position always remember that okay and if it doesn't occur over there what rules you have to keep in mind that is least number first part is least number see which of the following element is present in least amount here nitrogen is one fluorine is three nitrogen is in least amount so can acquire Center most position if this number is also equal then you can go for what you can go for least electronegative then you can go for what least electronegativity now you have understand electronegativity in depth what actually is electronegativity you have understand it it is tendency to attract shared pair of electron towards itself if you are not getting this as well then you will move on to the factor that is psi's largest which of the following structure has the larger size not the structure sorry the element the atom which has the largest size will acquire the center most position and the last is if it doesn't follows as well you can go with atomic number atomic number largest so the this is basically the rule number second which is modified further least number then least electronegativity then size largest then atomic number largest do remember this students clear everybody clear now the next part show shared pair of electrons between two atoms and unsured electrons on one atom okay so this is how you represent now only we are going to start it so no need to worry about it but yes first of all right all is all these rules now then I'm going to bring you some questions over here so students I guess everybody has written these rules right now let us proceed further we are going to now calculate the formal charge and also how to represent the structure first of all we will represent the structure we will take some cases and then we will start with the topic formal charges clear everyone so starting with the very first structure let us do now the Lewis Dot representation everybody let us start with let us start with Lewis [Music] Dot [Music] representation students let us start with Lewis Dot representation everybody so starting with the very first part that is H2 molecules now before the students let me tell you I have told you to calculate number of valence shell how you have to represent this okay representation representation of elements here I am doing representation of elements and then we will be looking up to the you know formation of a chemical bond over here in the case of molecules so first of all I am taking the case over here that is representation of elements in the case of let us consider hydrogen let us consider we have to represent hydrogen how we will represent we have to show the total number of valence electrons the total number of valence electrons is one so you will represent hydrogen and then one electron clear now let us take another case for example helium we know the total number of valence electrons two so how you are going to represent helium as 1 and 2. okay now for lithium how many valence electrons lithium is an atomic number three so it is 1 is 2 2 is 1 valence electrons is one what is valence electron electron in the outermost Shell First shell referral sequential first shell contain two electrons second shall contain only one so one is the valence electron so lithium can also be represented as like this Li then dot clear dot represents the total number of valence electrons now moving on to the fourth one let us take one more case let us take a case of carbon carbon has an atomic number six so it is configuration is one is two two is two two P two how many valence electrons four valence electrons no so you will represent carbon as one two three and four getting my point everybody getting my point is it clear now see let us take few more cases let us take in case of nitrogen nitrogen atomic number seven what is the configuration one is two how many electrons in the valence shell two s two two B three five electrons if if you don't understand by this way you can draw also first shell second shelf first shell contains two electrons second contain one two three four and five so automation five electrons that means you have to represent it by five so one two three four and five yes simple let us take a case of oxygen oxygen as an atomic number eight so it is one is two two s two two P four how many valence electron two plus four is six 6 valence electrons so oxygen is one two three four five and six clear everyone this is the way to represent for oxygen atom let us take case of chlorine now let us take a case of fluorine fluorine basically has an atomic number nine so one is two two s two P five how many valence electron two plus five that is seven electrons so fluorine will be represented as one two three four five six and seven clear everyone [Music] let us take case of sodium sodium as an atomic number 11 students so how you're going to represent it it is 1 is to 2 is 2 2 p 6 3s1 third shell is the outermost shell how many valence electrons ma'am one valence electron so sodium will be represented as like this yes okay let us take the case of magnesium now magnesium is an atomic number 12. how it will be represented one is two 2 is 2 2p6 3s2 that means how many valence electrons two valence electrons so two valence electrons let us take one more case [Music] aluminum aluminum atomic number 13 1 is 2 2 is 2 2 p 6 3 is 2 3 p 1 [Music] simple [Music] now see that means how many electrons in the valuation three clear by this way so by this way you represent elements okay this is the Lewis Dot representation of elements clear now we are going to start with the representation of molecules I would request each and everybody of you to please kindly please kindly write down all of these over here write down all of these over here clear clear clear clear clear okay now moving on to the representation thank you representation of molecules representation of molecules let us start with now we have done till J partner so this is going to be K part H2 we are going to start with H2 now see the very first thing that you need to do is very first rule is calculate total valence electrons calculate total valence electrons right so total valence electrons is going to be how much there are two hydrogens so 2 into valence electrons of single hydrogen now what are the valence electrons of hydrogen one so two into one is two electrons this is total valence electrons you have calculated what you have calculated total valence electron now see you are going to create a bond see there are two hydrogen right two hydrogen and they will contain at least single Bond initially create a single Bond and then calculate Bond pair electrons what I said you initially create a single Bond then calculate Bond pair electrons now what is a bond pair electrons [Music] what are Bond pair electrons Bond pair electrons Bond where electrons are those electrons which are basically present in a bond for example single Bond contains how many electrons always see single bond holds one and two electrons now double bond contains how many electrons it is going to be one two three and four four electrons now what about triple bond students it is one two three four five and six six electrons single one contain two electrons double will contain four electrons triple will contain six electrons so these are Bond pair electrons how many electrons are present in a single Bond over here so initially what we have to do is initially we have to create a single Bond now only a single Bond then you have to calculate Bond pair of electrons now you have represented a single Bond how many Bond per electrons ma'am Bond per electrons there is a single Bond so two electrons now calculate lone pair electrons loan pure electrons how you will calculate it you will calculate lone pair of electrons as total valence electrons [Music] total valence electrons minus Bond pure electrons total valence electrons minus Bond per electrons what are total valence electrons to what are bondware electrons two so lone pair comes out to be zero that means they have no extra electrons present over there that means this structure is complete now let us show the Lewis bot representation see this is first Hydrogen this is a second the first Hydrogen it hydrogen will show one one electron this is the representation right now what are they doing they are sharing their electrons they are creating a bond with this electrons when a bond is created this hydrogen now requires one more electron and this hydrogen also requires one more electron Creator creating a bond now see this hydrogen has two electrons in the outermost shell initially hydrogen had one as one as one configuration now there is one more electron with it right so it becomes one is two this hydrogen also becomes one is two that means it completes its duplet so it is stable now and this is the structure also there is zero lone perfect electron that means though no extra electrons over here hence this structure is the correct one what are lone pair of electrons the extra electrons which don't participate in bonding lone pair electrons or LP electrons foreign [Music] participate in bonding in bonding clear everyone is it clear to each and every one now this was the structure of H2 everybody write it down so that I can draw the next structure of ours for now we are going to draw for nf3 nf3 everybody done done [Music] okay now we are going to do with the part number j k l l part and we are going to draw nf3 calculate total valence electrons everybody first of all total valence electrons so for nitrogen how many valence electrons mam five for fluorine how many valence electrons seven how many fluorine three so this comes out to be 5 plus 21 that means mam 26 electrons 26 valence electrons now shows a single bond in each and every case now which is going to be the central metal atom nitrogen because it has least electronegativity secondly it has if you see the number it has least number so nitrogen will be the center most and then will be fluorine over here fluorine over here fluorine over here so how many Bond pair electrons you have represented one two and three bonds three bonds into each one contain two electrons so this comes out to become six electrons six Bond pair electrons are seen in this case now calculate lone pair electrons lone pair electrons mam is total valence electrons [Music] total valence electrons minus Bond pair electrons yes so total values electrons is 26 minus the bond per electrons this comes out to be 20 electrons how many alone per electron 20 now let us represent it see nitrogen has how many uh valous electrons in the outermost shell five so represent one two three four and five yes now comes for fluorine how many valence electrons in fluorine seven mam so this is first fluorine one two three four five six and seven the next fluorine one two three four five six and seven another fluorine one two three four five six and seven ma'am yes yes now students let us check the number of electrons they are holding see fluorine has seven electrons and it and is gaining one electron of nitrogen total eight electrons total how minimum eight electrons now see this seven plus one eight electrons seven plus one eight electrons let us talk in the case of nitrogen now see nitrogen one two three four five six seven eight nitrogen with also eight electrons eight electrons right now let us see see they are completing its octet eight eight eight eight eight electrons but let us see this over here there are total 20 lone pairs let us count loan per electrons now see one two three four five six seven eight nine ten eleven twelve thirteen fourteen fifteen sixteen Seventeen eighteen nineteen twenty you have to count those electrons which are not participating in bonding lone pair electrons are those electrons which don't participate in bonding so there are 20 lone pair of electrons hence found now there are some more rules that you should know that foreign if positive charge is written on any Compound on any molecule is written on molecule it is present at Central metal atom Central metal atom okay and if negative is written it is present on terminal atom it is present on terminal atom if positive is written it is present on the central metal atom if negative is written it is present on the terminal atom you will get to know in the upcoming uh you know examples but yes do write it down everybody also there is one more key concept that [Music] that Central metal atom Central metal atom can have more than eight electrons also but yes their initial rule the initial rule of the representation of molecules over here or of the octet rule Louis octet rule is to complete its octet right for example fluorine is completing its eight electron nitrogen is doing that another fluorine fluorine all of them is to attain stability in order to gather eight electrons in the outermost shell yes everybody everybody write it down so that I can move on to the next slide students now we are going to take the next case [Music] so the next case that is M case we are going to start is going to be about nh4 positive shall we start with nh4 positive now see calculate total valence electrons initially total valence electrons so for nitrogen it is five for hydrogen it is one total four hydrogen if plus one is written you have to subtract one right guys so it is 5 plus 4 minus 1 that is eight electrons how many electrons ma'am eight next step to show Single Bond now nitrogen hydrogen hydrogen hydrogen it has least remember nitrogen so it will be Central metal atom now count the bond pure electrons everybody how many bonds when four bonds into one bond holds two electrons some four into two is eight that means Bond pair electrons is eight electrons now let us see the lone pair electrons lone pair electrons what it is total [Music] valence electrons minus the bond pair electrons total valence electrons minus Bond per electron how many valence electron mam eight minus one pair how many it is eight electrons so this comes out to be zero that means there is no lone pair so yes it does not contain any lone pair of electrons next part many of you will say that ma'am now let us draw the structure completely nitrogen basically has you know five electrons in the outermost shell though yeah and hydrogen also has one one electron let us see it over here only nitrogen has one two three four five six seven eight completing its octet even hydrogen are completing its duplet so but what about this positive charge where we have to represent this positive charge you have to represent this positive charge at the central metal atom already told you in the previous slide students that if positive charge is written on the molecule it is present on the central metal atom if negative charge is written over there it should be represented at terminal atom so positive charge will be represented at Central metal atom clear so I have represented it over here clear everyone shall I move on to the next part yes everybody be fast now starting with the next part n part [Music] n part is O2 molecule right let us calculate total valence electrons let us take another color no so total valence electrons how many oxygen two into valence electrons of one oxygen so 2 into how many valence electrons are seen in the case of oxygen atom M6 now only we have calculated no six electrons so total comes out to be mum 12 electrons okay now show Single Bond initially between oxygen oxygen what are Bond pure electrons when Bond per electrons are only two electrons so what will be the lone pair electrons it will be total valence electrons minus the bondware electrons now total valence electron is 12 minus Bond pair is 2 this comes out to be mum 10 electrons let us represent them oxygen each oxygen holds X electrons so one two three four five and six now one two three four five and six this is the representation now see whether it's octet is complete or not one two three four five six seven no one two three four five six seven no that means no ma'am this is incomplete that means when what we have to do how we have to represent it this is so not correct one so see it is oxygen one two three four oxygen has one two three four single single Bond was already seen over here now one one electrons are left to one one electrons more will create one more bond that is double bond so it is one two three four five six seven eight one two three four five six seven eight that means this is the right way this is the right way in order to create a bond everybody first draw the structure draw the structure see octet was not completing octators not completing guys yes in this way octat was not completing seven seven electrons not eight over here see one two three four five six seven eight now see one two three four five six seven eight eight octets were completing that means that means this structure is now complete that means oxygen molecule holds double bond it holds double bond now check lone pair of electrons are the ten role lone pair of electrons still present one two three four five six seven eight wire because now Bond pair electrons get changed one per electrons are now four so lone pair electrons comes out to be 12 minus 4 that is eight electrons so yes we have drawn the correct structure now so by this way you know how a single bond is created how a double bond is created yes students everybody write this down done shall I move on to the next case yes shall I move on to the next case now we are going to take the case of NO3 negative I'm moving on to the next slide mno now we are moving on to The O Part [Music] NO3 negative first of all students you have to calculate what total valence electrons total valence electrons is nitrogen holds five oxygen holds six total three oxygen now it is negative charge so we are going to add one so this is five plus eighteen plus one that means it is 24 electrons now the next part over here is what next part is to draw the structure nitrogen holding three oxygen atoms yeah so the bond pair of electrons you are writing over here is three bonds into one Bond contain two electrons so six electrons what will be the lone pair electrons map it is total valence electrons total valence electrons minus the sorry minus the bond pair electrons now see total valence electron is 24 minus Bond whereas 6 so this comes out to be 18 electrons now we have to represent the structure C nitrogen basically holds you know uh five electrons one two three four and five now let's talk about the case of oxygen oxygen holes is six electrons basically so one two three four five and six similarly this oxygen one two three four five and six now this oxygen one two three four five and six now they are sorry they are creating a single Bond over here nitrogen if I talk about one two three four five six seven it is stable but oxygen is still not stable so what will happen over here the structure that means is incorrect so nitrogen again holding one two see nitrogen let us talk about here will be double bond between oxygen atoms now see one two three four five six and seven eight six oxygen atoms and twice of nitrogen holding another with single bond with oxygen oxygen atom single bond with oxygen oxygen atom everybody first of all draw this and I will explain you this part everybody draw the structure then we are going to explain this part over here everybody draw the structure then we are going to explain this part now see students here you will say that they hold seven electrons ma'am how you're going to explain this concept with the help of this negative charge see till here if you're drawing you will get confused why because now you will count the you know electrons in the outermost atom that is oxygen oxygen and nitrogen they won't be equal to the octet rule so how you are going to explain this concept with the help of formal charge now we will be introducing with the term formal charge and with the help of formal charge I will let you know that how students we do make the structures of the Lewis Dot Structure yes Louis do a structure in the case of negative charges we have to see the formal charges on individually each and every atom here we have three oxygen atom one nitrogen atom when you will calculate formal charge it will justify your structure but till then it won't justify your structure you will feel like no ma'am it's not completed OCTA that means it's not right one but yes after knowing that part you will get to know it yes students so now we are going to start with the formal charge what is the formal charge what actually is formal charge so formal charge is the charge that is present foreign particular atom the charge that a particular atom carries is referred to as the formal charge okay students now how to calculate what are the rules to calculate formal charge C formal charge in an atom in a polyatomic ion or compound can be defined as formal charge an atom in a Lewis structure now we don't have to calculate formal charge and complete molecule no formal charge is used for a single atom right now see you have to calculate total number of valence electrons in free atom now if you are calculating a formal charge for a single atom for example in any three negative I will talk you about to calculate formal charge in case of nitrogen that means the value you will put over here of total valence electrons will be of nitrogen not of the complete molecule till now we will calculating total valence electrons in order to know the structure but for the cases which have a negative charge or a positive charge in that case is to calculate formal charge take the valence electrons of a particular atom now minus total number of non bonding electrons that means you have to subtract lone pair of electrons complete lone pair of electrons and then subtract total number of bonding half into total number of bonding electrons that means Bond pair electrons so in uh simple terms I would say that what you have to do is take valence electrons you have to represent valence electrons by Q symbol okay minus the lone pair of electrons minus Bond pair electrons by 2. this is the formula to calculate what map to calculate for mull charge to calculate what map to calculate formula no need to worry the case of previous example the O example we will do it again but first of all we will calculate the formal charge everybody do write this formula very very important formal charge is equivalent to Total valence electrons minus lone pair electrons minus the bond per electrons by two now students more things about over here Lewis structure which has the smallest formula charge on each atom is most stable structure do remember that also sum of all the formal charges on an atom will be equal to 0 or the overall charge of a polyatomic ion see in redox reaction chapter you will understand about oxidation state the formal charge in detail but always remember when you are adding all the formula formal charge of all the atoms its sum will be equal to zero but yes if it is a not a neutral molecule either a positive or A negative one the sum will be equivalent to that number yeah okay so now um this is your first homework question for your today's class to students question number first as a homework you have to calculate the formal charge for the case of h3po4 here calculate the formula charge for p now what formula total values electrons of P minus lone pair on P minus Bond Pair by 2. first of all draw the structures as just as way I have told you calculate total valence electrons on the complete molecule then make a single Bond then find bow and bond pair electrons then draw the structure and then calculate the formal charge so first homework question for today's segment that we are going to discuss in next class also second homework question for today's class is to calculate formal charge on ph three on ph3 in the case of ph3 calculate on all the atoms phosphorus and hydrogen clear yes now let us read the ncrt Highlight students yes to make your Concepts Concepts more stronger than before now see Lewis pictured the atom in terms of positively charged kernels kernels are the positively transpicious the nucleus plus the inner electrons okay and the outer shell that could accumulate a maximum of eight electrons he further assumed that eight electrons occupy only the corners of a cube which surround the kernels does the single outer electron of sodium would occupy one corner of the cube because uh sodium contains one valence electron while in the case of noble gases all the eight Corners will be occupied because Normal gases contain eight valence electrons now this octet of electron represents a particular stable configuration so octat rule is basically when you are gathering a electronic configuration of group number 18 elements that is the stable or electronic configuration Lewis postulated that atoms achieve the stable octet when they are linked by chemical bonds yes one more thing about Lewis symbols what they have told you in the formation of a molecule only the outer shell electrons take place in the chemical combination that means whenever you are forming a chemical bond only the valence cell electrons will form the chemical bond yup which are honest valence electrons now the initial electrons are well protected and are generally not involved in the combination process so inertial electrons are not represented because they do not form any bond the outermost shell electrons will create the bond now JL Lewis and an American chemist introduced simple notation to represent valence electrons in an atom these notations are called Lewis symbols which we have already done for hydrogen helium lithium boron carbon nitrogen oxygen that is what is Lewis symbols clear everybody so homework I have already given you now students we shall be meeting in the next class I hope so this class was very helpful to you so we shall be meaning in the next class till then keep smiling keep learning thank you so much my dear students and have a good day okay