 Hydrogen? What is the atomic number of hydrogen? What is the position of hydrogen atom in clear table? The position of hydrogen atom is clear table. It is above our law. Is it an alkali metal? No. Why it is not an alkali metal? It is not an alkali metal. Why because the definition of alkali metal is these are the metal which reacts with water and forms hydroxide. Like suppose N A is an alkali metal, reacts with water and forms hydroxide. N A O H plus half of H 2. Proceed? Oh yeah. So this kind of reaction hydroxide does not show. It does not react with water. So the definition of alkali metal is these are the metal which reacts with water but hydrogen does not react. That is why it is not an alkali metal. N A O H plus half of N A O H plus half of N A O H. They have water and they react with water. N A O H does not react with this. So even a hydrogen reacts with H 2 O, it will still get hydrogen H 2 O? No, it will not get. No reaction is there. The reaction is not possible. See why this reaction takes place? It is the reason that N A gives N A plus plus 1 electron. And then this H 2 O from this O H minus will get attached to this. Hydrogen does not react with water. That is the one thing. See the point is the position of hydrogen atom it is placed in the first group on the top. These are the elements. Why hydrogen is placed here? Because if you see the property of hydrogen it has only one electron in the outer motion. It has tendency to gain one electron and forms duplicate. It has tendency to release one electron. It has tendency to share electron. All three possibilities are there. So if you see these three properties, alkali metal has tendency to release one electron. Sodium, it releases one electron. This property is similar to halogens. This property is similar to alkali metal. And this property is similar to carbon family. So we have three different positions of hydrogen can be here with halogens or with alkali metals or with carbon family. Why it is placed in group one? Because its outermost electron configuration is what? 1 S 1. Since the electron configuration is similar to that of other alkali metals that is why it is placed in group one. So this is placed in group one but it is not an alkali metal. In LCRT it is here. I am not discussing this as to go through it that there are few properties it has similar to that of halogens. Halogens actually just say halogens has property to gain one electron high electronegativities. Hydrogen also has property to gain one electron. Yes, and halogens are diatomic also. F2, X2 will write F2Cl2Br2 like that. Hydrogen also diatomic, H2. Similarly for alkali metals also hydrogen has few properties similar to alkali metals. Like it is electro positive in nature this is also electro positive. So like that there are many properties the reducing character is also there. And few properties similar to that of so there are few properties which is similar to that of halogens, alkali metals and carbon family it is given in LCRT just to go through it was not that important. What we have to discuss here is the preparation of hydrogen methods of preparation of hydrogen and then chemical properties of this and few compounds of hydrogen the most important part of this chapter is hardness. Hardness is what? What is hard water and soft water? There are some reasons for hardness of water temporary hardness, permanent hardness what is the reason for that and what is the removal how to remove the hardness of water. So if you have 5 minutes suppose before the exam and if you want to revise this chapter you should revise hardness part of it. Mostly you will get questions from there. And then some structure of H2O2 that is it for this chapter. So right now next the preparation of hydrogen the first method is by the action of water on active metal first one by the action of water on alkali metals this is reaction of hydrogen preparation of hydrogen by the action of water on alkali metals alkali metals you can also take alkaline earth metals active metals the elements of group 1 and 2 reacts with water and evolves hydrogen gas reacts with water and evolves hydrogen gas next slide the reaction is exothermic in nature to slow down the reaction we use amalgam amalgam means the metal that you are using amalgam of that alloy with H2O2 amalgam we use because the reaction is highly exothermic and what we say very fast also very fast also amalgam see you have metal it occupies the surface of the metal it absorbs it absorbs on the surface of this active surface area decreases in this case that is why the rate of the reaction also decreases the reaction slows down isn't that the same as putting in less metal is it like more metal plus amalgam active metal plus amalgam active metal plus amalgam you have suppose the active metal is not there plus amalgam so that won't react at all this just decreases the surface area isn't that the same as just putting in less of the same metal without amalgam as if you have more surface area that reaction is also possible what happens reaction is highly exothermic and rigorous in nature so it's very difficult to control there are chances of catching fire also in nature because the high heat evolves to control that reaction we use amalgam so that the reaction slows down less the energy evolves and we can control the reaction for that purpose we use it without amalgam also without hg alloy also the reaction possible but the rate is very high okay next point to write down by alkali solution by alkali solution metals like beryllium zinc metals like beryllium zinc aluminium react with boiling alkali solution means at high temperature we heat this solution boiling alkali solution and evolves hydrogen gas and evolves hydrogen gas so what do you mean metals like beryllium zinc and aluminium what kind of category is that definitely metals of group 1 you can take or group generally we take elements of group 2 or group 1 metals active metals okay so second period element second group sorry beryllium with NaOH alkali solution what it forms hydrogen gas goes out and it forms sodium beryllium Na2 BeO2 is sodium beryllium and H2 gas evolves into this if you take aluminium it forms sodium aluminium so is it because of amphoteric acid what so is it due to the amphoteric acid amphoteric acid is not required here because we are not using acid here only basic solution okay what happens this beryllium can displace this hydrogen metal okay depends upon the electrode potential which we haven't discussed here it can displace hydrogen gas from this next slide down by the action of acid on certain metals by the action of acids on certain metals right on by the action of certain metals on acid right on certain metals which displaces hydrogen gas from the dilute acid solution by the action of acids on certain metals there are certain metals which displaces hydrogen gas from the dilute acid solution okay for example zinc plus H2SO4 what is the product here we can have mg plus 2Hz okay see these metals are electro positive metals these are electro positive metal these metals are placed above hydrogen in the electrochemical series okay electrochemical series again we will discuss this in electrochemistry somewhere in between we have electrode potential of hydrogen electrode which is assumed to be okay assumed to be 0 and above this we have positive electrode potential E0 greater than 0 and below this E0 is less than 0 so we can take all those metals which has positive electrode potential which and those metals can displace hydrogen from this dilute acid solution all these are dilute acid solutions so this gives you ZnSO4 plus H2SO4 and TCl2 plus H2SO4 so what is the difference between this series and the reactivity series reactivity series of what difference is not there but we can use this series this reactivity with respect to dilute acid I will explain this what happens here see actually hydrogen is present here one thing is there that if electrode potential is more then that metal has more tendency to go under reduction okay electrode potential means reduction in potential okay so if you have two metals suppose M1 and M2 if M1 has more electrode potential than M2 and if you form a cell of these two electrodes in this M1 will be the reduction of electrode where the reduction takes place which is cathode and M2 will be oxidation right so what happens here Zn plus 2 you see that oxidation of zinc is 0 here here it is plus 2 hydrogen is plus 1 and here it is 0 so which one is going under oxidation and which one is going under reduction Zn is getting oxidized and hydrogen is getting reduced right so what we can say when zinc reacts with this it displaces nitrogen right and rose under oxidation it means we can write the E0 of Zn plus 2 to Zn that means the reduction potential plus 2 to 0 is less than E0 is less that is why it is going to get oxidized it is less than the E0 of H plus 2 can be negative can be positive depends upon the matter there are certain metals which have negative electrode potential certain metals have positive electrode potential means this reaction means all those metals whose reduction potential is lesser than to that of hydrogen can displace hydrogen some its value ok one thing I wrote here wrong this should be negative and this should be positive so reactivity series is this only when you have metals which has more you know oxidation potential that will displace the other metal from its valued solution that is the reactivity series more reduction potential more reactivity more tendency towards the reduction reaction of that