Nonmetals are generally considered poor conductors of electricity, acting instead as electrical insulators. This characteristic stems from their fundamental atomic structure and the way they form chemical bonds, which sharply contrasts with the conductive nature of metals. Nonmetals are chemical elements that tend to gain or share electrons when reacting with other elements, such as oxygen, nitrogen, and sulfur. Understanding their insulating behavior requires examining how electrical current moves through materials.
How Electrical Current Flows
Electrical current is the organized flow of charged particles through a material. In solid conductors, such as metals, these particles are electrons that are not tightly bound to individual atoms. Metals are highly conductive because their valence electrons are loosely held and become delocalized, forming a “sea” of electrons that move freely throughout the atomic lattice when an electrical force is applied. This abundance of mobile charge carriers allows electricity to flow easily through the material.
When a voltage is applied across a metal, these free electrons drift in a coordinated direction. These mobile electrons act as the carriers of the electrical charge, transmitting the current from atom to atom. The ease of electron movement defines a good electrical conductor. This mechanism of conduction requires a continuous supply of electrons not confined to a specific atomic orbital or bond.
Why Nonmetals Are Generally Insulators
Nonmetals typically form bonds through covalent bonding, which involves sharing valence electrons between atoms. In this bond type, electrons are held tightly in a localized space between the two atomic nuclei, rather than being free to roam throughout the structure. This tight localization means there are no mobile charge carriers available to initiate or sustain an electrical current.
Because electrons are held firmly within these covalent bonds, they cannot easily move in response to an applied electric field. This lack of delocalized electrons is the primary reason why most nonmetals, such as solid sulfur, phosphorus, and gases like oxygen and nitrogen, function as electrical insulators. Even when nonmetal compounds are dissolved or melted, they often do not produce the free ions or electrons necessary to carry a charge.
The Unique Conductivity of Carbon
The element carbon, specifically in its allotrope graphite, is a significant exception to the rule of nonmetal insulation. Carbon’s ability to conduct electricity depends entirely on its structural arrangement. In graphite, carbon atoms are arranged in flat, two-dimensional layers of interconnected hexagons.
Within each layer of graphite, every carbon atom uses only three of its four valence electrons to form strong covalent bonds with its neighbors. The fourth valence electron is left free, or delocalized, to move within that layer. These delocalized electrons can travel across the planes of carbon atoms, making graphite a good electrical conductor, especially parallel to the layers. This contrasts sharply with diamond, another carbon allotrope, where all four valence electrons are tightly bound in a rigid three-dimensional structure, making it a superb electrical insulator.