Sodium chloride, commonly known as table salt, is a familiar chemical compound whose ability to conduct electricity is often misunderstood. Electrical conductivity is a material’s capacity to allow the flow of an electric current. The simple answer is “yes,” but this property depends entirely on the salt’s physical state. Dry, solid table salt is an insulator, but once melted or dissolved in a liquid, it becomes an excellent electrical conductor. The mechanism of conduction in salt is fundamentally different from that in a metal wire.
The Difference Between Ionic and Electronic Conduction
The movement of electricity through materials falls into two main categories: electronic and ionic conduction. Electronic conduction occurs in metals like copper, where the charge is carried by the movement of delocalized electrons. These electrons are free to move throughout the material, allowing current flow even when the metal is solid.
Sodium chloride is an ionic compound composed of charged particles called ions. Sodium atoms become positively charged cations (\(\text{Na}^+\)), and chlorine atoms become negatively charged anions (\(\text{Cl}^-\)). For sodium chloride to conduct electricity, the current must be carried by the physical movement of these charged ions, a process known as ionic conduction. This movement is only possible when the ions are mobile and free to travel toward electrodes of the opposite charge.
Conductivity in Solid and Molten Sodium Chloride
The state of pure sodium chloride determines the mobility of its ions and its conductivity. In its common solid state, table salt forms a rigid, repeating three-dimensional crystal lattice. Within this lattice, the positive sodium ions and negative chloride ions are tightly locked into fixed positions by strong electrostatic forces.
Because the ions cannot physically move from their fixed points, solid sodium chloride cannot carry an electric current. It acts as an electrical insulator because it lacks both free electrons for electronic conduction and mobile ions for ionic conduction.
Once pure sodium chloride is heated to its melting point of about 801 degrees Celsius, the intense thermal energy overcomes the forces holding the lattice together. The solid transforms into a molten state, releasing the ions from their fixed positions. The resulting liquid is a strong electrical conductor because the mobile \(\text{Na}^+\) and \(\text{Cl}^-\) ions are free to move toward the oppositely charged electrodes, carrying the current.
How Salt Dissolves to Create an Electrolyte
The most common way sodium chloride becomes conductive is by dissolving in water to form saltwater. Water (\(\text{H}_2\text{O}\)) is a polar molecule, having slight positive and negative charges. This polarity drives the dissolution process when salt crystals are introduced to water.
The polar water molecules surround the ions on the crystal surface. The negative end of the water molecule is attracted to the positive \(\text{Na}^+\) ions, and the positive end is attracted to the negative \(\text{Cl}^-\) ions. This strong attraction, known as an ion-dipole interaction, pulls the ions away from the solid lattice structure.
This process, called dissociation, releases the formerly locked ions into the solution, where they become surrounded by water molecules. The resulting solution is a highly conductive liquid called an electrolyte, containing a high concentration of free-moving, charged particles. In this aqueous solution, the \(\text{Na}^+\) and \(\text{Cl}^-\) ions migrate through the water when an electric field is applied, using the same ionic conduction mechanism seen in molten salt. This explains why natural bodies of water and biological fluids are effective conductors of electricity.