Most materials formed by covalent bonds do not conduct electricity. However, some covalent substances exhibit electrical conductivity due to unique structural arrangements. Understanding this requires examining covalent bonds and the fundamental requirements for electrical conduction.
Understanding Covalent Bonds
A covalent bond forms when two atoms share pairs of electrons to achieve a stable electron configuration, typically resembling a full outer shell. This sharing occurs predominantly between non-metal atoms, allowing them to bind together into molecules or extended structures. The electrons involved in these bonds are usually localized, held tightly between specific atoms, and are not free to move throughout the material.
The Basis of Electrical Conductivity
Electrical conductivity depends on the presence of mobile charged particles that can move freely through a material. In most conductors, these mobile charge carriers are electrons. When an electrical voltage is applied, these free electrons are able to drift, creating an electric current. Materials that conduct electricity readily possess a “sea” of electrons that are not bound to any single atom, allowing for their easy movement.
Why Most Covalent Compounds Are Insulators
In most covalent compounds, electrons are tightly held within shared bonds between atoms. These localized electrons lack the ability to move freely throughout the substance. Without mobile charge carriers, electric current cannot flow, rendering most covalent compounds as electrical insulators.
Common examples include pure water, sugar, plastics, rubber, glass, and dry wood. Their electrons are strongly held within molecular or network structures, preventing electrical conduction.
Covalent Structures That Can Conduct
Despite the general rule, some covalent structures possess unique arrangements that allow for electrical conductivity. Graphite, an allotrope of carbon, serves as a prime example. Each carbon atom in graphite forms three covalent bonds with neighboring atoms within a flat, hexagonal layer, leaving one valence electron per atom unbonded. These remaining electrons are delocalized, forming an electron cloud that can move freely within the layers, facilitating electrical conduction.
Semiconductors, such as silicon and germanium, also feature covalent bonds in their crystal structures. In these materials, electrons are typically held in covalent bonds, but with the input of energy, such as from heat or light, some electrons can gain enough energy to break free from their bonds and become mobile charge carriers. This allows for controlled conductivity, which is fundamental to modern electronics. Doping semiconductors with impurities can further enhance their conductivity by increasing the number of free charge carriers.
Everyday Examples of Conductivity
Electrical conductivity is evident in many everyday materials. Metals, like copper and aluminum, are excellent conductors because they have a vast number of free electrons that can easily carry an electric current. They are widely used in electrical wiring.
Insulators prevent electricity from flowing. Plastics, rubber, and glass are used as insulating covers for wires and electrical components to ensure safety and direct current flow. Even pure water is an insulator, though the presence of dissolved impurities, like salts, can make tap water conductive. Graphite, often found in pencil lead, demonstrates the unique conductivity possible within certain covalent structures, allowing it to complete an electrical circuit.