Question

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

• A. 122pm
• B. 244pm
• C. 488pm
• D. 976pm

Answer 1

Answer: (B)

244pm

$NaH$ is a type of face centered cubic unit cell and has geometry of octahedral

The ${Na}^{\oplus }$ atom/$H^{\ominus }$ atom are surrounded by $6H^{\ominus }$ atom/ ${Na}^{\oplus }$ atom respectively.

The length between one Na and H atom is half of their edge length

i.e., bond length $=\frac{a}{2}$

where a=edge length

Given :-i) Edge length of $NaH=\left(a\right)=488pm$

To find:- Length of $Na-H$ bond$=?$

Formula: Bond length$=\frac{a}{2}$

$\therefore$ Edge length of $Na-H=488pm$- (given )

(pm is pictometer)

$\therefore$Bond length of $Na-H=\frac{a}{2}$

$=\frac{488}{2}$

Bond length of $Na-H=244pm$