Question

Pure sodium $(Na)$ is a good conductor of electricity because the $3s$ and $3p$ atomic bands overlap to form a partially filled conduction band. By contrast the ionic sodium chloride ($NaCl$) crystal is

• A. Insulator
• B. Conductor
• C. Semiconductor
• D. None of these

Answer 1

Answer: (A)

In sodium chloride the $N{a}^{+}$ and $C{l}^{-}$ ions both have noble gas electron configuration corresponding to completely filled bands. Since the bands do not overlap, there must be a gap between the filled bands and the empty bands above them, so $NaCl$ is an insulator.