Nonmetals represent a diverse group of chemical elements defined by the absence of metallic characteristics. They are predominantly located on the upper-right side of the periodic table, with the notable exception of hydrogen. Unlike metals, they are typically dull, brittle as solids, and exist across all three states of matter. These physical characteristics raise the question of whether nonmetals can be good conductors of heat and electricity.
The General Rule: Nonmetals are Insulators
Nonmetals are overwhelmingly classified as poor conductors, functioning instead as electrical and thermal insulators. This lack of conductivity is one of the defining physical properties that distinguishes them from metallic elements. Nonmetallic materials offer high resistance to the flow of electrical current. They are therefore widely utilized in applications where the controlled blockage of electricity is required, such as the plastic coating around copper wires.
Nonmetals are also poor thermal conductors. Common materials like wood, rubber, and plastics are used specifically for this insulating quality. Noble gases, such as neon and argon, are extremely poor conductors in their gaseous state due to their unreactive nature. This behavior contrasts sharply with the high conductivity exhibited by most metals, which efficiently transfer both electrical charge and thermal energy.
Electron Movement and Conductivity
A material’s ability to conduct electricity depends on the behavior of its valence electrons. In metals, these electrons are not tightly bound; they are delocalized and form a mobile “sea of electrons” that flows freely throughout the structure. This easy movement of charged particles enables metals to conduct an electrical current.
Nonmetals exhibit an atomic structure that restricts electron mobility. Nonmetal atoms generally form covalent bonds, sharing electrons tightly and localizing them between specific neighboring atoms. Because these electrons are held firmly in place, they cannot move freely to carry an electrical charge. This lack of delocalized electrons prevents an electric field from initiating a current flow through the material.
Thermal conductivity is linked to electron movement and the vibration of atoms within the lattice structure. In nonmetals, the absence of mobile electrons means heat transfer relies primarily on the vibration of atoms, known as phonons. This is a far less efficient process than the energy transfer facilitated by free electrons in metals. The tightly bound electrons and covalent bonding are the primary reasons nonmetals are ineffective at transporting energy.
The Unique Case of Carbon
Carbon presents an exception to the general rule in one of its structural forms, known as allotropes. Diamond adheres to the general rule, acting as an excellent electrical insulator. In diamond, every carbon atom is bonded to four others in a rigid, three-dimensional network, completely localizing all valence electrons.
Graphite
Graphite, conversely, is a notable conductor of electricity. This is due to its distinct, layered hexagonal structure, where each carbon atom is bonded to only three neighbors within a flat plane. The fourth valence electron is delocalized and free to move within that plane, creating mobile charge carriers. This arrangement allows graphite to conduct electricity along the layers, though it remains a poor conductor perpendicular to them. Graphite is also an exception in thermal conductivity, as its highly ordered structure makes it one of the best known natural thermal conductors.