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A network solid or covalent network solid (also called atomic crystalline solids or giant covalent structures) [1] [2] is a chemical compound (or element) in which the atoms are bonded by covalent bonds in a continuous network extending throughout the material.
Solids can be classified according to the nature of the bonding between their atomic or molecular components. The traditional classification distinguishes four kinds of bonding: [1] Covalent bonding, which forms network covalent solids (sometimes called simply "covalent solids") Ionic bonding, which forms ionic solids
These differences in the strength of force (i.e. covalent vs. van der Waals) and electronic characteristics (i.e. delocalized electrons) from other types of solids give rise to the unique mechanical, electronic, and thermal properties of molecular solids. [3] [4] [5] [8]
Covalently bonded solids (sometimes called covalent network solids) are typically formed from one or more non-metals, such as carbon or silicon and oxygen, and are often very hard, rigid, and brittle.
Very different bonding – strong covalent within the basal planes (planes where boron and nitrogen atoms are covalently bonded) and weak between them – causes high anisotropy of most properties of h-BN. For example, the hardness, electrical and thermal conductivity are much higher within the planes than perpendicular to them.
Such covalent substances are low-boiling-temperature liquids (such as ethanol), and low-melting-temperature solids (such as iodine and solid CO 2). Macromolecular structures have large numbers of atoms linked by covalent bonds in chains, including synthetic polymers such as polyethylene and nylon , and biopolymers such as proteins and starch .
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Metallic glasses, for example, are typically well described by the dense random packing of hard spheres, whereas covalent systems, such as silicate glasses, have sparsely packed, strongly bound, tetrahedral network structures. These very different structures result in materials with very different physical properties and applications.