Question

Sodium chloride has a crystalline structure made up of $ {\text{N}}{{\text{a}}^{\text{ + }}} $ and $ {\text{C}}{{\text{l}}^{\text{ - }}} $ ions. Why does $ {\text{NaCl}} $ not conduct electricity in solid state?
(A) Solids do not conduct electricity.
(B) The ions of $ {\text{NaCl}} $ become mobile only in molten state and are not free to move in solid state.
(C) The crystalline structure does not have ions.
(D) When a bond is formed between ions they lose their charges.

Answer 1

Hint: A well arranged three dimensional structure made up from the atoms, ions and molecules in a crystalline material is known as crystal structure. The presence of free ions in a material becomes the cause of conduction of electricity.

Complete step by step answer:
Crystalline structure: The description of the arrangement of the atoms, molecules or ions in a crystalline material is known as crystalline structure.
Crystalline structures have a particular well arranged three dimensional geometrical structure. All the bonds present between the ions, atoms and molecules in the crystalline structure have equal strength. And we all know that among all types of solids crystalline solids are more stable. In crystalline solids a long order arrangement of ions, atoms or molecules is present. And due to all these types of reasons sodium chloride does not conduct electricity in its solid state but conducts electricity in molten state because in molten state sodium chloride dissociates into ions and these ions help the charge to move from one end to another. In water the electrostatic attraction present between the oppositely charged ions breaks down and hence ions separate and become free to move.
 So from the above discussion we can conclude that the sodium chloride does not conduct electricity in solid state because ions of sodium chloride become mobile only in molten state and are not free to move in solid state.
Hence option (B) is the correct answer.

Note:
Mainly three types of crystalline structures are discussed in chemistry because most of the alloys crystallize with these structures. Those three crystal structures are; body centered, face centered and cubic close packed.