Elemental sulfur is not a good conductor of electricity; it is classified as an extremely poor conductor and functions as an insulator. This element, a bright yellow, brittle solid under normal conditions, is a non-metal with an atomic number of 16. Pure sulfur has a very low electrical conductivity, measured to be approximately \(1 \times 10^{-15}\) Siemens per meter (S/m). The inability of elemental sulfur to efficiently carry an electric current is rooted in its fundamental atomic structure and bonding characteristics.
Understanding Electrical Flow
Electrical conductivity depends on the presence of mobile charge carriers that can move freely within a material when an electrical force is applied. In solid materials, this movement is primarily facilitated by electrons. Materials that are good conductors, such as metals, possess “delocalized” or “free” electrons that are not tightly tethered to a single atom, allowing current to flow easily through the material. In contrast, insulators have their electrons tightly bound within the atomic structure. These electrons are highly localized, meaning they require a massive amount of energy to break free and move, making it nearly impossible for a charge to pass through.
Why Elemental Sulfur Fails to Conduct
Elemental sulfur is a non-metal that forms stable molecules through covalent bonding. Under standard conditions, sulfur atoms link together to form a crown-shaped, eight-atom ring molecule, represented by the formula S8. In the S8 ring structure, each sulfur atom shares electrons with its two neighbors, forming strong S-S single bonds. The electrons are tightly held within these covalent bonds and are localized between the two atoms sharing them. Because the electrons are firmly attached to their respective S8 molecules and cannot move freely throughout the bulk material, they cannot transport an electrical charge, resulting in a strong electrical insulator.
The Conductivity of Sulfur Compounds
While pure elemental sulfur is a poor conductor, this insulating property does not extend to all compounds that contain sulfur. When sulfur combines with other elements, particularly metals, the resulting compounds, known as sulfides, can exhibit vastly different electrical properties. Sulfides often form ionic or metallic bonds that dramatically alter the electron arrangement. Many metallic sulfides, such as iron pyrite (FeS2) or copper sulfides like covellite (CuS), function as semiconductors or even good conductors. This change occurs because the metallic or ionic bonding introduces the necessary electron delocalization or mobility that is entirely absent in the covalently bonded S8 structure.