Solid State part 1

追加: 2026-05-12

[00:00:00]now we are going to start the next chapter there is a solid state now what do you mean by solid first of all in solid state what is a solid what you may say solid is a state of matter like liquid and gas and plasma and that is b c we are having solid is another state of matter correct but still then i am asking you my same question what is a solid what do you understand with the term solid solid is defined as that what you can say form of matter which possess rigidity and hence possess a definite shape and a definite volume again i repeat solid is that state of matter is defined as that state of matter which possess rigidity as a result it has got a definite shape and a definite volume now the thing is that that is we come to know solids are rigid they have got a different shape and hence they have got a definite volume they have large number of free surfaces a solid has we have studied all these things now what what leads to this particular factors this factor which i said no it has got definite shape definite volume it has reached it has got large number of uh free surfaces it is having high density on it what leads to this particular factors two things are there one is the strong intermolecular forces between the atoms or the molecules or the ions in the solid that means between the constituent particles of the solid because of that whether it is atoms or the design so this molecule because solids are of different types we'll study now different types of solids are there molecular solids ionic solid network solid covalent solid will be studying it now so based upon that we can say that the constituent particles have got strong inter-molecular force of attraction between them point number one and secondly the thermal energy which decides stability of a particular substance is very very low the thermal energy is in the lowest state and the intermolecular force of attraction is the maximum when these two factors are coming closer in a particular substance then the substance possess this properties what is that it is rigid it is having high density it is having a definite shape it is having a definite volume it is having large number of free surfaces and so on which you have studied in the lower classes about the type of solid all right remember it what is that i said the two fact the two things are the two factors which is responsible for the characteristics of the solid is that one is the intermolecular force of attraction is very very strong very very strong whatever the solid it is whether designing solid or molecular solids or polar solids or hydrogen bonded solids or coal and solids whatever the solids are the metallic solids inter molecule force of attraction should be very strong and secondly so as to have the solid in the stable state the thermal energy should be in the lowest state all right these two factors you need to understand first now solids again is of two types what is that one is your crystalline solids crystalline solids and another is your amorphous solid amorphous now let me tell you one one thing here children that is amorphous uh term is no more used nowadays it is known as micro crystalline that means the scientists are of the opinion that that there is nothing which is in the powder state even the powder uh one i'm referring to the powder isn't it if you even if a substance if you observe it under a powerful microscope in the powder set you will find there are minute particles there are some nano particles are there in the crystalline state the nanoparticles are being present so hence nowadays we use a term that is micro crystalline this particular one is known as micro crystalline state okay amorphous state is also otherwise known as now we will see some differences between these solids now which solids are crystalline solids all metals we consider metals and the compounds in the ionic state they are all is in the crystalline solids all right all the solid elements that is it can be metals it can be non metals and the compounds in the ionic state in the solid state they are coming under what you can say crystalline solids now amorphous solids are nothing but a rubber glass it is pitch pitch we can say that then tar then fuse silica then plastics then polythene they are coming under amorphous solids we can see that now if you see first the arrangement of the crystalline solids arrangement of what the constituent particles in crystalline solids it follows a long range order whereas in amorphous solids it follows a short range order means what do you mean by long range order in short range order means long range order means if you look at the solid like suppose this is solid if you look from this side what is that it is circular if you look from the other end it is also circular that means what you find is that by looking at any of the cross section when you are seeing the crystalline solids if you look at any other cross section of the crystalline solid you can judge what is the shape of that particular solid i can judge it because that particular cross section remains the same throughout the solid am i able to make you understand what is that i said that is you if you see this particular solid you can see here it is circular not it it is circular here also this end also is circular so if you take the cross section of the solid suppose i break it this one here and what i like it i'll get a circular suppose i break it here whatever i'll get a circular so looking at the cross section at any point you can judge what you can say the shape of the solid that is called as long range order that means the order means arrangement of the solid is same through that means if it is ah what you can say cylindrical it is same throughout the cross section is being seen throughout but the arrangement of this solid is being seen throughout so that is called as long range order if it is cubical it will be cubicle through if it is cuboidal it will be cuboidal throughout so if you break the cross if you break that particular solid in any cross section you will find that the shape is the same throughout that is called as long range order we can say that long range order clear fine now next is after that we will come to the short range order short range order amorphous solution short range order means after a certain extent you will find it is uh cubicle then you will find a risky buddha then it will find this cylindrical but in this way the shape will not be the same throughout it will be different all right it will be different in different cross sections you will be finding out that is called a short range order so amorphous solids are short range because the shape is not the same throughout suppose you will get it crystalline ah if sorry cubic cubicle then after uh what against a certain distance after certain length after certain cross section you'll find it cuboidal after certain cross section you will find it again it is circular or it is wrong not it or it is quadrilateral in this way so the shape you will be differing we can say that the cross section will be differing so that is called as amorphous solid so you can see that next if you cut a crystalline solid it gives a sharp cleavage yes if you cut it suppose an iron plate if you cut it you will see it's a sharp cleavage it is so sharp that it shines when the light falls upon it what happens it shines but it gives a sharp cleavage but an amorphous solid gives a blunt cleavage when you cut it when you break it it does not break uniformly it breaks in an uneven manner all right it breaks in an uneven manner for example glass glass is coming under amorphous solid something alright when the glass breaks does it break in even manner no uneven you'll be finding out this sort of this sort of you'll be finding out all right this one uneven manner it is clear okay so in this way what you find is that it does not it has not got sharp cleavage it has got a blunt cleavage you can see that when a crystalline solid is being cut it ah when the light falls upon it all right what happens is that it reflects the light because it is bright it is having a luster but amorphous solid does not have that luster it does not have that particular except for you we can say that graphite iodine and all those things ah that is graphite we can say that clear in this way now next is what you find is that uh crystalline solids due to this particular reason they have got a high melting point or a sharp melting point you'll find out but amorphous solid they have got a range of melting point now i can give an example you read in organic chemistry that temperature ranges from 525 to 575 kelvin for example ethene plus hydrogen in presence of 525 to 575 kelvin gives what is that nothing but ethane gas ethyl alcohol in presence of congestion is over 140 to 160 degree celsius so what you find is that amorphous solids when they react or when they when they are heated or when they are boiled all right they do not have a sharp melting point or sharp boiling point what they have they have got a range of range of melting point you can see that due to this particular reason because their constituent particles are not the same throughout their arrangement is not the same throughout the cross section is not the same same throughout so for that particular purpose it has got a range of melting point clear now next is what you find is that crystalline solids they are anisotropic in nature or anisotropic so to say anisotropic in nature crystalline solids and this is isotropic in nature what do you mean by anisotropic anisotropic means that is what you find is that the properties like electrical conductivity thermal conductivity refractive index all right these are the physical properties what i am saying so what you find that this particular properties physical as well as chemicals so you find that these properties is different in different directions why because the arrangement of the molecules in crystalline solid is different in different directions but in case of amorphous solids these properties electrical conductivity magnetic conductivity thermal conductivity refractive index is the same in all the directions why because the arrangement of the solid is also is the same in all the directions okay now let us see first let us come to the crystalline solids the arrangement let us take sodium chloride n a plus c l minus again n a plus c l minus c l minus n a plus again c l minus n a plus again i am taking n a plus then c l minus again that is n a plus c l minus and this side is average all right and this side is arranged so what you find is that see the uh what you can say the if i if i if i take the diagonal i need to have one more here so let me write it here small one let me write it here that is c l minus then it is n a plus then it is cl minus then it is n a plus because it is what you find is that same rule okay so again what you find is that that is c the arrangement in diagonally c l minus a 1 is l minus you see the arrangement here n a plus l minus n plus a minus l c you see the arrangement in this diagonal what is that n a plus n plus n plus so the arrangement is different in different directions so the properties is also different in different directions so hence it is called as anisotropic in nature aristotle so crystalline solutes are anisotropy because we see the arrangement here you see the arrangement here you see the arrangement here it is different in different directions due to which the properties are also different in different directions which is called as anisotropic but in isotropic it is same through how for example let us say oxygen it will be o o two o two same through all right it will be same throughout we can say that the arrangement is same in all the dimensions in this way what you find is that now in the same oxygen is a gas it's a gasser it's not a solid yes i know that you condense it cool it you'll be getting a solid for example you you consider that carbon dioxide it forms what dry ice how do you get carbon dioxide it's a gas you cool and solidify the what you can say gas then what happens it's solidifies to form dry ice it's a solid but it we can get the solid in this way of course in the natural state it is not available in the surveys but we can solidify it or not yes that's it that is what i am saying clear in this way this there are certain differences between amorphous solids and crystalline solids similarly amorphous solids are said to be as pseudo solids pseudo pseudomeans false all right crystalline solids are known as true solids now why amorphous solids are pseudo solids because even if it is solid but it's not crystalline in nature it flows how can you say it flows for example glass all right if you if you see the or what you can say the window panes of the old buildings or the window panes of the old buses you find that it is at the bottom it is thicker and the top is thinner you can move it in this way clear and you will find the old buses or in the old buildings of window panes it has been stuck somewhere in the middle suppose you have opened the glass and you you have opened it and it is being stuck somewhere in the middle then it does not move similarly suppose if you are having um a showcase in your house a glass is there so you understand what is the source when you have brought this okay you find that the the glass panes are moving very freely but after few years you find it does not move freely why because the base becomes thicker how it becomes thicker because due to temperature and pressure and also due to gravity the glass molecule flows from higher level to the lower level which is known as annealing the process is known as the annihilation takes place year after year temperature pressure and gravity the glass molecule flows and due to which the base becomes thicker the top becomes thinner if you are having what you can say the old this sort of what is that so case you can see it the top is what you can say thinner it is it is moving in this way but the base becomes thicker it does not move so it does not move freely but when you brought it when you purchase it new then it is very fine it is moving freely moving the pins we can see the glass pins why because the same thing similarly you can see the old window pins it appears milky the glass appears milky all right even the specs after a few years if you're having an old specs you find that somewhere some sports is appearing so what you do is that you just take out the specs and you rub it you rub it you see some what you can say some spots you see and you rub it but that that spots you cannot remove it by rubbing because internal arrangement has changed the internal arrangement has changed of course nowadays the specs are available the glasses are available which does not change the internal arrangement so many so many glasses i'm not going to those particular one but the ordinary glasses i'm talking to the ordinary glasses you'll find that is the internal arrangement changes for that purpose you'll find somewhere it is milky it is hazy it does not appear clear to you it appears translucent it's not transparent why same reason due to temperature pressure and due to gravity the glass molecule flows i am talking about ordinary glass mind it here it flows and due to this particulation the molecular arrangement changes and hence it appears somewhere milky somewhere transparent clearly that's the reason so these are the difference between amorphous solids and crystalline solids so to say thank you