Chapter 29, Problem 14Q

To determine

Why $NaCl$ crystal is a good insulator (based on energy band)

Answer to Problem 14Q

Solution:

It requires large energy to create a conduction electron by raising an electron from the valence band to the conduction band.

Explanation of Solution

The 3s shell of $Na$ is partially filled, there is one electron in the shell. The 2p shell of $Cl$ is partially filled, with five electrons in the shell.

In sodium chloride ($NaCl$ )one electron from the 3s shell in $Na$ is transferred to the 2p shell in $Cl$, which results in filled shells for both ions. When we consider many ions, the resultingbands in $NaCl$ are either completely filled (the valence band)or completely empty (the conduction band). It requires large energy to create a conduction electron by raising an electron from the valence band to the conduction band. Due to this high energy $NaCl$ is a good insulator.