Question

Coordination number of $N{a}^{+}$ ion in $NaCl$ is 6 and that of caesium ion in $CsCl$ is 8.This is because:

• A. I.P of $C{s}^{+}$is less than $Na$
• B. size of $N{a}^{+}$ is less than $C{s}^{+}$
• C. attraction of $N{a}^{+}$ is higher than $C{s}^{+}$
• D. None of the above

Answer 1

Answer: (B)

size of $N{a}^{+}$ is less than $C{s}^{+}$

$NaCl$ and $CsCl$ have similar formula. However, they have different structures.

The radius ratio of $NaCl$ lies in the range of 0.414-0.732. Hence, it has a coordination number of 6, which is the octahedral arrangement. On the other hand, the radius ratio of $CsCl$ lies in the range of 0.732-1.0. Hence, it has a coordination number of 8. that is, it has a body-centered cubic arrangement.

The difference in the ranges of radius ratio in $NaCl$ and $CsCl$ is because of the fact that the size of $N{a}^{+}$ is less than the $C{s}^{+}$.

Hence, option B is correct.