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As this example shows, there can be no sharp boundary between molecular and network covalent solids. Intermediate kinds of bonding: A solid with extensive hydrogen bonding will be considered a molecular solid, yet strong hydrogen bonds can have a significant degree of covalent character. As noted above, covalent and ionic bonds form a continuum ...
Similarly, yellow arsenic is a molecular solid composed of As 4 units. [37] Some forms of sulfur and selenium are composed of S 8 (or Se 8) units and are molecular solids at ambient conditions, but converted into covalent allotropes having atomic chains extending throughout the crystal. [38] [39]
Solid-phase electrical conductivity: Variable, [6] depending on the nature of the bonding: network solids in which all electrons are used for sigma bonds (e.g. diamond, quartz) are poor conductors, as there are no delocalized electrons. However, network solids with delocalized pi bonds (e.g. graphite) or dopants can exhibit metal-like conductivity.
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.
In chemistry, a formula unit is the smallest unit of a non-molecular substance, such as an ionic compound, covalent network solid, or metal. [1] [2] It can also refer to the chemical formula for that unit. Those structures do not consist of discrete molecules, and so for them, the term formula unit is used.
Such covalent substances are usually gases, for example, HCl, SO 2, CO 2, and CH 4. In molecular structures, there are weak forces of attraction. Such covalent substances are low-boiling-temperature liquids (such as ethanol), and low-melting-temperature solids (such as iodine and solid CO 2).
At pressures higher than 110 GPa and temperatures around 2000 K, nitrogen forms a network solid, bound by covalent bonds in a cubic-gauche structure, abbreviated as cg-N. The cubic-gauche form has space group I2 1 3. Each unit cell has edge length 3.805 Å, and contains eight nitrogen atoms. [23]
However, structural determinations of vitreous SiO 2 and GeO 2 made by Warren and co-workers in the 1930s using x-ray diffraction showed the structure of glass to be typical of an amorphous solid [7] In 1932, Zachariasen introduced the random network theory of glass in which the nature of bonding in the glass is the same as in the crystal but ...