Question

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

Answer 1

Given - Unit cell edge $=a=488pm$

Let $r_{+}$ and $r_{-}$ radius of cation and anion,

$\sqrt{2}a=2(r_{+}+r_{-})$

$(r_{+}+r_{-})=\frac{a}{\sqrt{2}}$

$r_{+}+r_{-}=\frac{488}{1.414}=345.12pm$

Hence, Bond length between nuclei is $345.12pm$.