Network solid
Atoms bonded covalently in a continuous network throughout the material.
A network solid, also known as a covalent network solid, atomic crystalline solid, or giant covalent structure, is a chemical compound or element in which atoms are bonded by covalent bonds in a continuous network extending throughout the material. In such solids there are no individual molecules; the entire crystal or amorphous solid may be considered a macromolecule, with formulas represented by simple ratios of component atoms as a formula unit.
- also known as
- covalent network solid, atomic crystalline solid, giant covalent structure
- bonding type
- covalent bonds in a continuous network
- examples
- diamond, quartz, graphite, boron nitride, silicon carbide
- common properties
- very hard, high melting point, generally insoluble
- solid-phase conductivity
- variable (poor for sigma-bonded solids, metal-like for those with delocalized pi bonds or dopants)
- liquid-phase conductivity
- low
Lore & Background
Network solids include diamond, with a continuous network of carbon atoms, and silicon dioxide (quartz), with a continuous three-dimensional network of SiO2 units. Graphite and the mica group of silicate minerals consist of continuous two-dimensional sheets covalently bonded within the layer, with other bond types holding the layers together. Disordered network solids are termed glasses, typically formed on rapid cooling of melts so that little time is left for atomic ordering.
Reader's Guide
Network solids are significant because their structure—continuous covalent bonding throughout the material—gives them distinctive properties: very high hardness, high melting points (since melting requires breaking covalent bonds rather than weaker intermolecular forces), and general insolubility in any solvent due to the difficulty of solvating such a large molecule. Their solid-phase electrical conductivity varies: those using all electrons for sigma bonds (e.g., diamond, quartz) are poor conductors, while those with delocalized pi bonds (e.g., graphite) or dopants can exhibit metal-like conductivity. In the liquid phase, conductivity is low because the macromolecule consists of neutral atoms, so melting does not free new charge carriers. These materials contrast with molecular solids, ionic solids, metals, layered materials, and polymers, each having different bonding types and properties.
Did You Know?
- In a network solid there are no individual molecules; the entire crystal or amorphous solid may be considered a macromolecule.
- Disordered network solids are termed glasses, typically formed on rapid cooling of melts.
- Graphite and mica consist of continuous two-dimensional sheets covalently bonded within the layer, with other bond types holding the layers together.
- Network solids with delocalized pi bonds (e.g., graphite) or dopants can exhibit metal-like conductivity.
Frequently Asked Questions
What is a network solid?
A network solid is a material in which every atom is covalently bonded to its neighbors in one unbroken, three-dimensional lattice, so the entire crystal is essentially a single giant molecule rather than a collection of small discrete units. It also goes by the names covalent network solid, atomic crystalline solid, and giant covalent structure.
What are the most famous examples of network solids?
Diamond, quartz, graphite, boron nitride, and silicon carbide are the go-to examples fans usually cite. Each one shows how the same continuous-covalent-bonding idea can produce wildly different hardness, appearance, and electrical behavior depending on the atoms and geometry involved.
Why do network solids have such extreme hardness and very high melting points?
Because the covalent bonds run continuously through the entire structure, there is no weak intermolecular gap to exploit when trying to pull the material apart or melt it. That is why diamond tops the Mohs hardness scale and requires temperatures well above 3,000 °C before it finally loses its crystalline form.
Can a network solid conduct electricity?
In the solid state the answer is mixed: purely sigma-bonded networks like diamond are excellent insulators, while materials with delocalized π-electrons (such as graphite) or intentional dopants can carry current almost like a metal. Once melted, however, network solids generally show very low conductivity because the continuous bonding framework is destroyed.
How is a network solid different from a molecular solid?
A molecular solid is built from discrete, individually identifiable molecules held together by weaker intermolecular forces, whereas a network solid has no separate molecules at all—every atom belongs to one continuous covalent framework. That is why chemists represent network solids with a simple whole-number formula unit rather than a true molecular formula.
More in Chemical Bonding And Structure 1-21
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