Question

how many atoms are there in a single unit of an FCC lattice?

Answer 1

4 atoms. Becuase at each corner you have 1/8th of an atom and at each face you have 1/2. \[({1\over 8} \times 8 )+({1\over 2}\times6)=4\]

Answer 2

this is what a FCC lattice unit cell is like. one half of a molecule on every every of the six face, and one-eighth on every of the 8 corners. so

so total no. of units per cell= (1/8 * 8) + (1/2 * 6) = 1+3 = 4