Question

assume that aluminium atom can be arranged as shown in figure if each atom has radius 1.43A.what is length of side

Answer 1

A) Well, if it’s FCC, then you have 8 corner atoms, each shared with 7 other unit cells- that’s 1 atom total. Plus you have 6 face atoms each shared with one other unit cell, so that’s 3 more. Total of 4 atoms per unit cell, in any FCC lattice. 

B) That means how many atoms is each atom touching. It’s a close-packed structure; so 6 in it’s plane, with 3 above and 3 below, total of 12.

C) Remember they’re touching along the face axis of the cube, so 4 radii equal the length of the unit cell times the square root of 2. You can do this simple calculation!