Question

In fcc unit cell what fraction of edge is not covered by atoms

Answer 1

In FCC the relation between radius and edge length is given as

[math]4*R = a*(√2)[/math] // R is the radius of the atom

or [math]a = 2√2*R[/math] // a is edge length of unit cell

Edge uncovered can be calculated as : [math]a-2*R = ~0.83R[/math]

Percentage edge uncovered : ([math]0.83R/a)*100 = 29.27[/math]%

Hope this helps.