Sugar (sucrose) is a common carbohydrate that readily dissolves in water, yet it is a non-conductor of electricity. The core reason for this lack of conductivity is that sugar is a molecular or covalent compound. It fundamentally lacks the mobile, charged particles required to carry an electric current. A sugar molecule is electrically neutral and cannot break down into ions when placed in an electric field.
The Requirement for Electrical Flow
Electrical conductivity requires the flow of charge-carrying particles through a material. A substance must contain a sufficient number of particles that are both electrically charged and free to move in response to an electric field. This movement of charge occurs through two primary mechanisms depending on the material type.
In solid conductors, such as metals, the mobile charge carriers are delocalized electrons. These valence electrons are not bound to a single atom but form a “sea of electrons” that can drift freely throughout the metallic structure. This movement allows for a continuous flow of charge when a voltage is applied.
In liquids or solutions, electricity relies on the movement of free-moving ions, which are atoms or molecules carrying a positive or negative charge. Ionic compounds, like table salt, release these ions when dissolved in water or melted. The movement of these charged ions toward oppositely charged electrodes completes the circuit and allows current to flow.
Sugar’s Covalent Structure
The fundamental difference between sugar and conductive materials lies in their bonding structure. Sugar molecules are formed through covalent bonds, involving the sharing of electrons between carbon, hydrogen, and oxygen atoms. This sharing creates discrete, intact molecules where all electrons are tightly held within the bonds, known as localized electrons.
Because the electrons are shared, the overall sugar molecule remains electrically neutral. These neutral molecules are held together in the solid state by relatively weak intermolecular forces, such as hydrogen bonds. Consequently, even in its solid, crystalline form, sugar acts as an insulator because it lacks delocalized electrons or mobile ions to transport a charge.
Why Dissolving Sugar Does Not Create Ions
When sugar is placed in water, it dissolves, but this process does not result in electrical conductivity because it fails to create mobile ions. Dissolving, or dissolution, is a physical process where intact, neutral sugar molecules separate and become evenly dispersed throughout the water. The covalent bonds within the sugar molecule itself remain unbroken.
This is distinct from dissociation, which occurs when an ionic compound like table salt dissolves. Salt breaks apart into separate, charged particles: positively charged sodium ions (\(\text{Na}^+\)) and negatively charged chloride ions (\(\text{Cl}^-\)). Since sugar molecules remain whole and neutral, a sugar solution contains no significant number of mobile charge carriers, making it a non-electrolyte and a poor conductor.