I am a student of XII std and unable to get the answer for this question:

A forms a CCP (cubic close packing). A atoms are in the corners, B atoms are at the alternate face what is the formula of the compound?

My understanding is that

A atoms : 8 x 1/8  = 1
B atoms = 3 x 1/2 = 3/2

Formula of compound = A₂B₃

OR

A atoms : 8 x 1/8  = 1
B atoms = 6 x 1/2 = 3

Formula of compound = AB₃

Is my understanding correct or which is the correct formula for the compound?
 

I think you will find that whilst you have the corner contributions correct, the question (can we see the exact wording) refers to alternate face centered cubic, which has B atoms on only two opposite faces. Therefore there are only two B atoms, not 6 or 3.

Is this homework?

Thanks for the details - the question is as in the main post. The question is from a test paper which I am trying to solve.

Can you please explain your solution with some information?

1 hour ago, StudentXIIStd said:

Thanks for the details - the question is as in the main post. The question is from a test paper which I am trying to solve.

Can you please explain your solution with some information?

This is taken from Solid State Chemistry by Smart and Moore.

I have highlighted the relevant bits on the two pages.

 

the second try is correct. for FCC, contribution per unit cell is 4. the at atom at corner contributes 1/8. if we ignore that, we get 3. (B is not at corners). thus, we get AB₃ only. 

check it out in your NCERT. it's explained in a great way. 

Edited October 17, 20187 yr by muskan