Anetwork solidorcovalent network solid(also calledatomic crystalline solidsorgiant covalent structures)[1][2]is achemical compound(or element) in which the atoms are bonded bycovalent bondsin a continuous network extending throughout the material. In a network solid there are no individualmolecules,and the entirecrystaloramorphous solidmay be considered amacromolecule.Formulas for network solids, like those forionic compounds,are simple ratios of the component atoms represented by aformula unit.[3]
Examples of network solids includediamondwith a continuous network of carbon atoms andsilicon dioxideorquartzwith a continuous three-dimensional network of SiO2units.Graphiteand themicagroup ofsilicate mineralsstructurally consist of continuous two-dimensional sheets covalently bonded within the layer, with other bond types holding the layers together.[3]Disordered network solids are termedglasses.These are typically formed on rapid cooling of melts so that little time is left for atomic ordering to occur.[4]
Properties
edit- Hardness: Very hard, due to the strong covalent bonds throughout the lattice (deformation can be easier, however, in directions that do not require the breaking of any covalent bonds, as with flexing or sliding of sheets in graphite or mica).
- Melting point: High, since melting means breaking covalent bonds (rather than merely overcoming weaker intermolecular forces).[5]
- Solid-phaseelectrical conductivity:Variable,[6]depending on the nature of the bonding: network solids in which all electrons are used forsigma bonds(e.g. diamond, quartz) are poor conductors, as there are no delocalized electrons. However, network solids with delocalizedpi bonds(e.g. graphite) ordopantscan exhibit metal-like conductivity.
- Liquid-phase electrical conductivity: Low, as the macromolecule consists of neutral atoms, meaning that melting does not free up any new charge carriers (as it would for an ionic compound).
- Solubility: Generally insoluble in any solvent due to the difficulty of solvating such a large molecule.
Examples
edit- Boron nitride(BN)
- Diamond(carbon, C)
- Quartz(SiO2)
- Rhenium diboride(ReB2)
- Silicon carbide(moissanite, carborundum, SiC)
- Silicon(Si)
- Germanium(Ge)
- Aluminium nitride(AlN)
See also
editReferences
edit- ^"Properties of solids".www.chem.fsu.edu.Retrieved2021-02-08.
- ^"12.7: Types of Crystalline Solids- Molecular, Ionic, and Atomic".Libretexts.2018-05-20.Retrieved2021-02-08.
- ^abSteven S. Zumdahl; Susan A. Zumdahl (2000),Chemistry(5 ed.),Houghton Mifflin,pp. 470–6,ISBN0-618-03591-5
- ^Zarzycki, J. Glasses and the vitreous state, Cambridge University Press, New York, 1982.
- ^Ebbing, Darrell D., and R.A.D. Wentworth. Introductory Chemistry. 2nd ed. Boston: Houghton Mifflin, 1998. Print.
- ^Brown, Theodore L.; LeMay, H. Eugene Jr.; Bursten, Bruce E.; Murphy, Catherine J. (2009).Chemistry: The Central Science(11th ed.). Upper Saddle River, NJ:Prentice Hall.pp. 466–7.ISBN978-0-13-600617-6.