Answer to Question #202578 in General Chemistry for Jerry

Question

Ni crystallize s in a face - centered cubic structure. The radius of nickel atom is 1.25 A°. 

What is the length of the unit cell edge in angstrom?

Answer 1

A face centered cubic structure has each face with four corner atoms and one center atom. That center atom means the corner atoms do not touch along the edge of the cube because they touch along the face diagonal instead. Here are a couple of slides from my lecture on solids. You can see that the face centered cell has a face diagonal that equals 4 atomic radii. If you know the atom size you can then calculate the size of the cell edge.