The ability of an ionic compound to conduct electricity depends entirely on its physical state. Understanding why this is the case requires a look into the nature of these compounds and the fundamental principles governing electrical flow.
Understanding Ionic Compounds
Ionic compounds form when a metal atom transfers one or more electrons to a non-metal atom. This transfer results in the formation of charged particles called ions: positively charged cations and negatively charged anions. These oppositely charged ions are held together by strong electrostatic forces of attraction, forming a highly ordered, repeating three-dimensional crystal lattice in their solid state.
The Fundamentals of Electrical Flow
Electrical current is the movement of charged particles. For a material to conduct electricity, it must contain charged particles that are free to move. These mobile charge carriers can be either electrons, as seen in metals, or ions. Without the ability for these charged particles to move, no current can flow through the substance.
Ionic Compounds and Electrical Conductivity
Solid State
In their solid, crystalline form, ionic compounds do not conduct electricity. Although composed of charged ions, these ions are held firmly in fixed positions within the rigid crystal lattice. The strong electrostatic forces prevent them from moving freely to transport charge. Consequently, no mobile charge carriers are available to facilitate electrical flow through the solid material.
Molten (Liquid) State
When an ionic compound is heated to its melting point, it transforms into a molten state. The added thermal energy overcomes the strong electrostatic forces holding the ions in the crystal lattice. This allows the ions to break free and become mobile. With this free movement, they can respond to an applied electric field, migrating towards oppositely charged electrodes and conducting electricity effectively. The high concentration of mobile ions makes molten ionic compounds excellent electrical conductors.
Aqueous Solution (Dissolved in Water)
Many ionic compounds readily dissolve in water, forming an aqueous solution. Water molecules surround and separate the individual ions from the crystal lattice in a process called dissociation. These separated ions become hydrated and are then free to move independently throughout the solution. The presence of these mobile, charged ions allows the solution to conduct electricity. The greater the concentration of dissolved ions, the higher the electrical conductivity of the solution.