 A compound made of particles A, B and C forms CCP lattice forms CCP lattice in the lattice in the lattice ions A occupy in the lattice ion A occupy the lattice points ion A occupy the lattice points and ions B and C occupy alternate tetrahedral void alternate tetrahedral void if all the ions if all the ions along one body diagonal if all the ions along one body diagonal is removed along one body diagonal is removed then the formula of the compound is formula of the compound is did you understand the question alternate tetrahedral first of all what is the position of tetrahedral void location of tetrahedral void last class we have discussed of tetrahedral void present at the body diagonal okay how the tetrahedral void forms it forms by the combination of one cornered atom and three phase centered atom okay like this cornered atom this cornered atom this phase center this phase center and this phase center this whatever corner you can draw from this phase you can draw from this corner so in this cube we can draw three phase from this one is this another one is this another one is this right so this cornered atom is in contact with this phase center this phase center and this phase center all these four atoms are in contact so once you look at this structure this kind of question to find out the formula of the compound is very common you will get this question definitely in some of the examples okay so this cornered atom actually this cornered atom is in contact with a wall of phase the center you can a phase center or this corner so we can draw one more phase is this this phase center and we have one more phase here that is this phase center okay it does not look like silver but you take this I will just shift this here to make you understand this is there okay so this is the phase center one two and three okay this phase center atom one two and three it forms a triangle here these are all these are in contact okay and this is also contact in this three this one so here you see here we have a void over here this is tetrahedral okay so one diagonal is here not this point this is a poly diagonal so what tetrahedral void will be here another tetrahedral void will be somewhere here that is what we discussed last class that on a diagonal we have two tetrahedral void present okay and the tetrahedral void forms by one cornered atom and three adjacent phase center okay so on a poly diagonal we have two tetrahedral void and at the center what we have center to get out there octahedral void okay center we have octahedral void so what they what is the question the question is atom a forms what lattice point ccp lattice means what ccp means accession ccp of the same thing and a forms ccp lattice it means k present at cornered plus phase center right b and c presented alternate tetrahedral void this come over a poly diagonal pay we have b over here we have a c over okay or either be not okay b c means for a void diagonal we have one atom of b and one atom of c okay so how many v atoms are present in this lattice four because we have total how many right I don't avoid eight total and on the poly diagonal we have only one v atom and we have how many poly diagonals four poly diagonals so number of these four and number of c is also what right but all four b is not present in the lattice because the question is what this is what the number of a b and c what is the number of a will have here is again four corner means what eight into one by eight phase center means six into one by two this is four okay so number of a atom is four number of b is for number of c is four we have to find out the formula so if you with this particular you know question the formula is a b and c if nothing is removed then but what is the question we are removing all atoms along the body diagonal okay suppose a body diagonal here sk along do be atom our house will work right so have we removed atom a in this no okay okay corner and face center so it's a long remove for the door corner atom with a remote a each is what they're not going to be body diagonal k long concept of present squad okay so when you draw the poly diagonal we have two a atom one b and one c I was going to come then what is the formula of the compound so on my back right so we have removed two a atoms and that is present with the corner not at the face so you have to say a what is the number of a present in this that is out of eight corners to have been removed correct so what we what is that six and what is the contribution of one one by eight plus phase center means no change because we don't have eight a atom now it is only six corners which are occupied by atom a six into one by six into half because face center to remove three plus three by four which is something on 15 by four correct okay number of a atom is this b secret man a 15 by four a five when you get answers like this and both a and b are option you got it so it's not a question very common in this chapter you'll get this question definitely in any of the example okay so just you need to find out the effective number of atoms present you should know the position of void okay when the question says that atoms along the body diagonal have been removed then you should know what all atoms are present along the body diagonal so we have two cornered atoms two tetrahedral void and one octahedral void so whatever atoms are present in tetrahedral void and octahedral void that will be removed okay we'll find out the effective number of atoms a b and c and the issue of that with the common of the compound so I'll give a okay you got a question for this please go a compound is made up of particles a and b particles a and b a forms fcc packing b occupies all octahedral void b occupies all octahedral void if all the particles if all the particles along the plane shown in figure if all the particles along the plane shown in figure are removed then the simplest formula of the compound is this plane you see these two edges we are removing all the atoms present along this plane first of all you need to find out if a or b like I have told you not to take the reference of the classroom okay classroom plane you find out along that plane what all atoms are present okay all those atoms forms fcc and b presented octahedral void correct a fcc form okay b forms octahedral void it means because octahedral void presented all edge center and body center right so we'll write down here edge center and body center okay edge center and body center now what is this plane this edge and the bottom of the edge this plane you imagine okay this plane you imagine so this plane is going this way okay so what all atoms are coming so one body center two corner there two corner here and what edge also we have that edge in this edge and this face center also right so you don't know face center is well or a face center the level of face center and level of face center front wall or your back wall I don't know this plane passes through these two face center this body center two corners edge center edge center into corners okay so all these along this plane we are removing all the atoms I don't know let's see that okay so how many a we are removing how many corner a we are removing corner a two and two four right so we have only four corner a present four into one by eight how many face center we are removing two face center we are removing four into half okay how many edge center we are removing yes enter what center to a center we are removing et cetera contribution one by four so one by four into how many et center atom we have total left edge we have total total sorry we have 10 etch 10 et cetera total don't know and one body center we are removing it is five by two two or four okay and this is also five by two so answer okay was it tough only just you need to know keep just plain okay understood okay next question time a crystal is made up of particles x y and z x forms fcc x is fcc y occupies all octahedral void z occupies all detrahedral void if all the particles along one body diagonal are removed the formula of this x 3 y 2 z 4 option are not there x y z 2 x 2 y z 2 x 8 y 4 z 5 x 5 y 4 z 8 x 8 y 4 z 5 i don't know so c option is there okay what is the question x forms x forms fcc right so cornered to a space center or y forms octahedral octahedral void say octahedral void and z z detrahedral how many detrahedral voids are there eight so that was there eight i will do that octahedral void is ten four and what will happen four right so simple formula will happen other we don't remove anything and this is the formula okay but we have removed the atoms along the body diagonal means some look don't detrahedral void remove per thing right so here i guess six one octahedral void remove per thing three on the body diagonal here along carry move current no atoms two cornered atoms so six into one by eight plus six into half this is 15 by four so one says x 15 by four y 3 6 so it is x 5 y 4 z 8 so this kind of questions will get density relations questions also will get formula given you just you have to use the formula