Electrical conductivity measures a compound’s ability to allow the flow of electric current. This property is fundamentally determined by the material’s internal atomic structure and the type of chemical bonds holding it together. To predict if a substance will conduct electricity, one must first determine if it contains charged particles and then assess if those particles are free to move. Understanding a compound’s chemical classification is the most reliable predictive tool.
The Requirement for Mobile Charge Carriers
The flow of electricity requires the presence of mobile charge carriers. Without particles that possess an electrical charge and the freedom to move under an applied electric field, a substance will behave as an electrical insulator. This mobility is achieved through one of two distinct mechanisms.
One mechanism involves the movement of delocalized electrons, which are not permanently bound to a specific atom. These free electrons form a mobile “sea” throughout the material, allowing current to pass easily. The second mechanism relies on the movement of entire charged atoms or molecules, known as ions. These ions carry the charge when they move freely within a liquid or solution.
Predicting Conductivity Based on Chemical Structure
A compound’s chemical structure and bonding type provide the primary way to predict its electrical behavior. Compounds formed by metallic bonding, such as copper or aluminum, are excellent conductors because their valence electrons are shared across the entire structure. This “electron sea” model means that delocalized electrons are inherently present and highly mobile, making metals a benchmark for high conductivity.
Ionic compounds, like sodium chloride, are formed by the electrostatic attraction between positively and negatively charged ions. Despite containing charged particles, these compounds are electrical insulators in their solid form because the ions are locked into a rigid crystal lattice. The strong attractive forces prevent the ions from moving, inhibiting the flow of charge.
Covalent compounds, formed by atoms sharing electrons to create neutral molecules, are poor conductors or insulators in all states. Substances like sugar, oil, or plastic do not possess delocalized electrons, as all valence electrons are localized within the specific bonds between atoms. Since these compounds are composed of neutral molecules, they lack the mobile ions required for the secondary conduction mechanism, confirming their status as insulators.
The Role of Physical State
The physical state of a compound is a factor, especially for substances that rely on mobile ions for conduction. For ionic compounds, changing the physical state provides the mobility required to conduct electricity. When an ionic solid is melted or dissolved in a solvent like water, the rigid lattice breaks down, freeing the positive and negative ions.
These liberated ions become mobile charge carriers, allowing the liquid or solution to conduct current effectively. A solution of a dissolved ionic compound is known as an electrolyte because it conducts electricity through the movement of ions. Changing the state of a covalent compound, such as melting ice or boiling alcohol, does not create charged particles, so they remain electrical insulators. Metallic compounds conduct electricity in all physical states, maintaining high conductivity even when molten, since their electron sea remains mobile.