Question

If the edge length of NaH unit cell is 488pm(picometre), what is length of Na-H bond if it crystallizes in the fcc structure????

Answer 1

In fcc structure of NaH, Na atom is present at the corners and H is present at the edge centre.  

Bond Length= Edge Length/ 2 

= 488/2 = 244pm 

Answer 2

Hey !!

NaH has fcc structure similar to that of NaCl

Thus, edge length of NaH = 2 ( r(Na⁺) + r(H⁻)

         2 (r(Na⁺) + r(H⁻) = 488 pm

∴  r (Na⁺) + r(H⁻) = 244, which is Na-H bond length.

Hope it helps you !!