Question

Pure sodium (Na) is a good conductor of electricity because the 3s and 3p atomic bands overlap to form partially filled conduction bands. By contrast the ionic sodium chloride (NaCl) crystal is:
A. Insulator
B. Conductor
C. Semiconductor
D. None of these

Answer 1

The ionic sodium chloride crystal is present in solid state. In ionic sodium chloride crystals the electrons are arranged in a close packed system so that the ions cannot move freely from their respective places.

Complete step by step answer:
Conductors are defined as the compound or atom which can conduct electricity easily. Solid sodium is good conductors of electricity as in sodium there is no band gap between the valence band and conduction band as they overlap with each other. The electrons are continuously available in the closed orbital which can conduct electricity.
In ionic solid crystals of sodium chloride, the electrons are arranged in a closed pack system therefore the ions are not free to move. For the conduction of electricity the movement of ions is necessary. Therefore, the ionic crystal of sodium chloride is an Insulator. In insulators the band gap between the valence band and conduction band is so large that the electrons cannot jump to the conduction band from the valence bond.
Thus, ionic sodium chloride crystals are insulators.
So, the correct answer is “Option A”.

Note:
When the ionic sodium chloride is dissolved in water it dissociates to give its constituent sodium cation and chloride anion. Due to this property the ionic sodium chloride acts as a strong electrolyte and the solution of sodium chloride is used in conduction of electricity as the ions are free to move in the solution.