 Hello everyone a very warm welcome to each one of you. So as you can see we will start with some basic concepts of chemistry today So let's start So starting from the ward itself chemistry chemistry is Something which deals with the structure Properties different kinds of properties. It can be physical chemical properties of substances, right? And if we try to know that this structure or Properties of what structure and of properties of different different substances? So in order to know the structure and different properties we need to Go to the micro level. So we need to see what are these substances made up of? So we will see the basic unit of each substance So we need to know regarding atoms We need to know regarding molecules and Then we will go on to studying different compounds. Okay now So different theories were given different laws were given. So basically atoms will combine with each other to form molecules right, so Different theories where different laws more precisely were put forward and there was one person Dalton Forward all the laws into a theory. So we call it as Dalton's atomic Theory, what does Dalton's atomic theory states the first most important postulate of Dalton's atomic theory is matter Is made up of Very small indivisible particles or we can say in the indivisible means We cannot break that substance further into smaller components. So indivisible particles Which are known which was called as atoms This was the first postulate that was given by Dalton and he also Said that atoms of Same element so there are different elements. We know that in periodic table in 10th grade Also, we have studied the periodic table and we have seen there are so many elements, right? So atoms of the same element No matter from where we take it where the origin is coming from same elements will have same properties same properties Identical properties what what do we mean by identical properties like for example size shape Weight that means mass all these things will be identical if it is from the same element now From this point only Another point comes up that atoms of Different elements will have Different properties that means they will be different in all aspects mass size shape and all those so these are The three points that was given along with the fourth point now this particular fourth point is based on law of Conservation of mass so according to Dalton Atoms can neither be created nor be destroyed so Dalton's atomic theory was given in around 19th century But before that itself this law of conservation of mass was given by Antoine Lavoisier So according to the law of conservation of mass It was stated if I talk about only this law of conservation of mass It stated that during any chemical or physical chain. I will write the law here particularly Then we will discuss about this Yes, so it states law of conservation of mass states that during any chemical or physical change The total mass of our products will be equal to the total mass of the reactants That means suppose if I have taken a plus b is giving me C plus d and I know that the mass of a is x mass of b is y For C it is z and for D it is let's say a Okay now According to law of conservation of mass x plus y should be equal to z plus a This was given by Antoine Lavoisier So this is the particular concept from which the balancing comes up So why do we need to balance any reaction because of Law of conservation of mass we know that mass is conserved now so Now this last statement provided the mass has not undergone Conversion into energy. What does this mean? So sometimes what happens in especially in case of our? Nuclear reactions whenever there is any nuclear reaction Nuclear reaction means that means where there is new nucleus involved. Okay, so that particular case What happens is there is a lot of energy involved That means when we are talking about nuclear reactions, either we are talking about fusion Or we are talking about fission. You have heard about nuclear bombs and stuff, right? So we are talking about fusion and fission here So whenever we are talking about a nuclear reaction, what happens is there is a There is a certain amount of mass which gets converted into Energy so definitely the mass will be changed so that time what happens the law of conservation of mass LCM fails there but mass is getting converted to Energy it is not lost. It is not like it is going vanished out of somewhere So it is getting converted to energy so we can say that law of conservation of mass and energy is conserved now according to the equation we have studied in physics E is equal to MC square right so here we can see that mass and energy are Like two forms of the same thing. Okay, so mass can either get converted into energy energy can also get converted into mass Okay So please remember this that law of conservation of mass will fail in case of nuclear reactions But if we talk about law of conservation of energy that is gonna stay conserved now So four pointers we have seen in Dalton's atomic theory now coming to the fifth point Fifth point states that Atoms now I told you that atoms will combine with each other to form Different substances right molecules or compounds so atoms of different elements will combine and They will combine in a fixed Whole number ratio fixed whole number Ratio they will combine in that ratio only all the ways when forming compounds Now this is also a particular law that has been given by Joseph Proust. Okay, so this is known as law of definite proportion Law of definite proportion it was given by Joseph Proust. So basically it has been made into a theory by Dalton Now we have to know a little bit more regarding law of definite proportion. What does law of definite proportion states? Let's see the statement first Now the law of definite proportion states that any compound doesn't matter what its origin is Will contain the same elements in Same definite proportion by mass. We will take one example here Let's say we have Suppose we want to analyze carbon dioxide. So carbon dioxide we can prepare by a lot of synthetic process So first process, let's see as carbon. We can just be acted with oxygen heated and it can form CO2 Another method is carbon monoxide with Oxygen if we heat it then also we can get CO2 we can get From decomposition of calcium carbonate as well Will give calcium oxide plus CO2 So I want to analyze these three samples of carbon dioxide that I have got from three different synthetic methods When I will analyze it. I will see that the composition The composition of CO2 I am analyzing I will see that the mass of carbon and oxygen it will always be Carbon is how much? 12 oxygen is how much? 16 plus 16 32 So we will see it will always be in this ratio if we It will always be Reacting or Combining in a definite proportion by mass that is our three is two eight in all these three samples We will be seeing the same thing one more example we can take let's say Cupric carbonate So cupric carbonate is an example from ncrt itself Naturally obtained cupric carbonate was taken and as well as synthetic also it was taken So the percentage of copper Percentage of carbon and percentage of oxygen was analyzed in this particular sample got from both the sources So it was seen that in natural The percentage copper was fifty one point 35 and Percentage carbon was nine point seven four percentage oxygen was thirty eight point nine one When synthetic cupric carbonate was analyzed same percentage was up to thirty one point three five nine point seven four and Thirty eight point nine one so it states that no matter what the origin is The definite proportion by which the elements are combining to form the compound will be constant always Now here also there are certain conditions under which this particular Law of definite proportion fails does not hold true. So we will see in which which conditions so conditions Under which the law of definite proportion LDP Fails Generally it will fail in two conditions first condition is when The compound is made from different isotopes for example H2O and B2O now H2O the masses let's say 2 is to 16 so always Hydrogen and oxygen will be Combining in the ratio of one is to eight But similarly if we talk about D2O now D2O will be what D2O will be four is to 16 so it will always be mixing in the ratio one is to four so definitely this Composition is different. So whenever we will be using Isotopes of the same compound same element. Sorry isotopes of the same element Then this particular definite proportion might change. So there the LDP will fail and the second situation where the LDP will fail is in case of Non stoichiometric compound non stoichiometric compounds are compounds in which The composition is not fixed. So there is no fixed composition No fixed composition for example titanium hydride this hydrogen can be present In the amount of 1.5 to 1.8 So we can see that there is no definite mass ratio in this particular compound. There will be no definite Mass the ratio so definitely the law of definite proportion will fail in this case So these are the two conditions under which LDP will fail So the next law is our law of multiple proportions. This was proposed by Dalton himself Now the statement for this particular law is when two elements will combine for example We can straight away take one example and understand this particular statement Suppose nitrogen a certain compound contains nitrogen and oxygen Now the compound can be many types It can be either N2O or let's say it can be nitric oxide or it can be N2O3 or it can be N02 or it can be N2O5 Now we can see that it is made up of two elements But the number of compounds formed is not one. It is more than one Now we have to make the mass of any one of this particular element constant So here I am making the mass of nitrogen as constant. So if I say here in this compound What is the mass of nitrogen 14 plus 14 it will be 28 Here it is 14 Here it will be again 28 Here it is again 14 and here it is 28. Now coming to the oxygen here it is 16 16 again Here it is 48 32 and here it will be 18. Now I have to make any one of the Elements mass to be constant So here particularly I am making the nitrogen mass as constant. How can I make it constant? I can multiply these two with two If I multiply these two with two Definitely, I have to multiply the oxygen mass also with two So this will give me a mass of 32 and this will give me a mass of 64 And both of this will become 28 28 So you can see now all this nitrogen mass have become constant and that is nothing but 28 so keeping this nitrogen mass constant the mass of the oxygen that is Combining with this nitrogen if I take the ratio of that masses of only oxygen You can see here it is 16. So 16 is 2 Here it is 32 32 is 2 48 is 2 64 is 2 18 So if I Reduce this into the lowest fraction possible lowest ratio. It will give me a ratio of 1 is 2 is 2 3 is 2 4 is 2 5 So that means what the masses keeping the mass of nitrogen as constant the mass of the oxygen that is combining with this fixed mass of This nitrogen bears a whole number ratio and this whole number ratio is this number Okay, so this is particularly meant by our law of multiple Proportion so in many compounds that will be seen one such example will be our let's say carbon monoxide and co2 So here carbon masses constant it is 12 12 here the oxygen masses 16 here it is 32 so keeping the carbon mass constant the oxygen the Amount of oxygen that is combining with each one of them is in the ratio 16 is to 32 that is nothing but 1 is to 2 that is the simple whole number ratio now same thing we can do for H2o And H2 O2 as well So same Keeping this hydrogen mass constant as 2 and 2 again it will be around 16 to 32 which mass Simple whole number ratio is bearded by Oxygen so it will be again 1 is to So this is all about our law of multiple proportion. So by seeing the compound itself how to recognize that this particular two compounds are Following law of multiple proportion or not so it definitely The element in both the compounds here also it should have hydrogen oxygen here also It should have hydrogen oxygen suppose. I have given you let's say H2o and HCl Will this show law of multiple proportion definitely not why because here the number of elements which are present are hydrogen and oxygen and here the elements which are present at hydrogen and chlorine so definitely These two are not equal. So the elements has to be equal in both the components Now coming to the next law that is our galusax law Now galusax law states that When gases react now, I'll first of all, I'll take one example. Let's say I am combining N2 and H2 So when I am reacting these two gases they will react in a way that the Volume in which they are reacting that volume will be or a simple whole number ratio to one another and Also to any gaseous product that has been For to the volume of any gaseous product that has been formed. So N2 and H2 forms what NH3 It will form NH3 now if I balance this if I balance this Here we will have three and here two Now what I'm trying to say is I have taken One volume so according to galusax law one volume of N2 will react with three volumes of H2 to give two volumes of NH3 this this particular law Was known as galusax law now here we have taken volume So let's say if we take some realistic volume. Let's say we have taken 20 ml Okay, so if N2 I am taking 20 ml then how much H2 do I need to take One volume needs three volume so 20 ml should require at least 60 ml of H2 and How much of NH3 will be formed? 20 ml Not 20 ml 20 ml into 2 correct So it will be 40 ml of NH3 that will be formed One more example we will see One more example. We will see H2 plus Cl2 is giving HCl to HCl So suppose if I say I Have been given 50 ml of H2. I have been given. Okay. It's not like according to the balance reaction emcee Suppose one person has given you 50 ml of H2 and 100 ml of Cl2 Now we can clearly understand that this 50 ml Will react with the Will not react with 100 ml. It will react with 50 ml only because according to galusax law one volume of H2 will react with One volume of Cl2 to give two volumes of HCl So if I have been given with 50 ml of H2 and 100 ml of Cl2 if I consider 100 ml Do I have 100 ml of H2? I don't have 100 ml of H2. So 50 ml of H2 will react with 50 ml of Cl2 and Form how much of HCl it will form 100 ml of HCl why 100 ml 15 to this Two two volume is there. So definitely if one volume is 50 ml two volume should be 100 ml What a question here in the end product that means in the reaction mixture What are the gases which are left? So we will definitely have the product that is 100 ml of HCl But there will be another gas what gas which one gas which gas was left in excess Cl2 gas was left in excess how much amount? 50 ml So this 50 has reacted with 50 ml only but initially we were given with 100 ml of Cl2 So definitely 50 has been left. So this will be the composition of the resulting mixture When we are given with 50 ml of H2 plus 100 ml of Cl2 Initially we are given with this and we are left with this So we are able to detect what will be the Composition of the resulting mixture with the help of this Galussat's law and definitely in coming topics We will be using this particular concept In understanding limiting reagent this particular law will be very very helpful We will be studying that in later lectures now coming to the next law Our next law is Avogadro's law and this is the last law of our laws of chemical combination basically So the statement says that when certain physical conditions like temperature pressure remains constant then if I take let's say Here I have taken two boxes Okay, or maybe you can consider this as a particular volume. So let's say here we have 50 ml of H2 gas Okay, and here we have another box another particular volume Which is also 50 ml of CO2 gas these are the two gases we have taken both the volume are same So it states that the volume of all gases Equal volume equal volume of all gases will contain equal number of molecules, so if this particular volume contains X molecules of CO2 Then if this is container A this is container B if this contains X molecules of CO2 This should also contain X molecules of Now before this Avogadro's law one more theory was put forward by Bersilius He told that equal volume of all gases should contain equal number of atoms but that was a statement which was like Analyzed and it was seen that how can a particular gas contain like equal volume of all gases contain equal number of atoms because gases have individual identity only as molecules right gases will exist as molecules have you heard about That hydrogen gas is existing as hydrogen atoms only that happens only in case of noble gases helium Neon argon and all that but if we talk generally about gases they do exist in The form of molecules their independent existence is valid only in form of molecules So it is better to say that equal volume of all gases will contain equal number of molecules But will it contain equal number of atoms? Let's see So here no one important term comes up that is atomicity Atomicity what is atomicity number of? atoms in a Molecule it can be any molecule so Here we have X molecules of CO2 now one molecule of CO2 contains how many atoms One atom of carbon Plus two atoms of oxygen so total it contains three Atoms so if I say what is carbon dioxide's atomicity? It will be It will be three So if I say what is carbon dioxide's atomicity it will be three now Similarly if I try to do that for age two so for age two it will contain two two atoms of hydrogen so definitely that atomicity will be two so One molecule of CO2 is containing three mat three atoms So X molecules of CO2 will contain how many atoms? Three into X so three X atoms it will contain So in this chamber a We have X number of molecules But we have how many atoms in chamber a we have three X atoms But if we talk about chamber B we have X molecules of age two, but how many atoms do we have we have? two X atoms Why two X atoms because definitely one H two molecule will contain How many atoms two so X H two molecules will contain how many atoms two into X two X atoms So this is the difference So molecules Will be same in equal volume of all gases, but atoms might be different Atoms might be same also at times for example here if I take instead of CO2 if I would have taken Cl2 Then here also the atomicity is two when will the atoms be of two gases also be seen when their Atomicity will be same so one more point we can write if Atomicity is same The two gases in question if their atomicity is same then Molecules as well as atoms Both will be Same, but if atomicity is different then the number of atoms will vary so in this case we can say that volume of any gas is directly proportional to number of molecules present So this was basically our avogadro's law. We will be Understanding this concept more as we proceed with this particular chapter so with this we complete all the five laws of chemical combination and Dalton's atomic theory so this was the basics Before we start with more concept Thank you everyone. See you in the next lecture You