1. Strong Covalent Bonds: Covalent network solids are held together by a continuous network of strong covalent bonds. These bonds are much stronger than the intermolecular forces (like hydrogen bonding, dipole-dipole, or London dispersion forces) that hold solvent molecules together or that could potentially form between the network solid and the solvent.
2. Lack of Polarity: Most covalent networks are composed of nonpolar atoms. They have no significant dipole moment and cannot form strong interactions with polar solvents.
3. Lack of "Breakable" Sites: Unlike ionic compounds or molecular solids, there are no readily identifiable sites in a covalent network where solvent molecules could break apart the structure. Breaking the network would require breaking the strong covalent bonds.
4. High Melting Points: The strong covalent bonds in these solids result in extremely high melting points. Most common solvents have much lower boiling points and are not capable of providing enough energy to break the network and dissolve the solid.
Examples:
* Diamond: A covalent network of carbon atoms, it is insoluble in all known solvents.
* Quartz (SiO2): A covalent network of silicon and oxygen atoms, it is essentially insoluble in water or other common solvents.
Exceptions:
While covalent networks are generally very insoluble, there are some exceptions:
* Some covalent networks can dissolve in highly reactive solvents: For example, certain covalent networks might dissolve in strong acids, bases, or highly reactive oxidizing agents. These solvents can react with the network, breaking the bonds and dissolving the solid.
* Specific interactions can occur: Even if the solvent is not highly reactive, some covalent networks might exhibit limited solubility in specific solvents due to specific interactions, such as weak hydrogen bonding.
In summary: The combination of strong covalent bonds, lack of polarity, and lack of breakable sites in covalent network solids makes them generally very insoluble in common solvents. While there might be exceptions, these factors make dissolving them in common solvents a very challenging task.
