Question

An element crystallises in `f.c.c.` lattice having edge length `400 p m`. Calculate the maximum diameter, which can be placed in interstitial sites without disturbing the structure.

Answer 1

For the face centred cubic lattice (fcc)
`"Radius (r)"=(a)/(2sqrt2)=(("400 pm"))/(2xx1.414)=141.4"pm"`
For octahedral void
`2(r+R)=aor 2R=a-2r`
`2R=(400-2xx141.4)=117.16"pm"`
Diameter of the bigger sphere 2(R) = 117.16pm