1. Strong Bonds: Covalent crystals have strong covalent bonds between the atoms, resulting in a rigid and well-defined structure. The covalent bonds are formed by the sharing of electrons between atoms.
2. High Melting and Boiling Points: Covalent crystals have relatively high melting and boiling points due to the strong interatomic forces. The strong covalent bonds require a significant amount of energy to break, resulting in higher melting and boiling points.
3. Insulators: Covalent crystals are generally poor conductors of electricity and are classified as insulators. The electrons in covalent crystals are strongly localized within the covalent bonds between atoms, and there are no free electrons available to carry electric current.
4. Hardness: Covalent crystals can be hard and resistant to deformation, as the strong covalent bonds prevent the atoms from moving past each other easily. Examples include diamond (covalent network solid) and graphite (covalent sheet solid).
5. Solubility: Covalent crystals are typically insoluble in water and other polar solvents due to their nonpolar nature. The covalent bonds between atoms are nonpolar, so they do not interact well with polar solvents.
6. Low Electrical Conductivity: As mentioned earlier, covalent crystals are poor conductors of electricity due to the lack of free electrons. The tightly bound electrons in covalent bonds prevent the movement of charges.
7. Low Thermal Conductivity: Covalent crystals have low thermal conductivity, which means they are poor conductors of heat. The strong covalent bonds and rigid structure hinder the transfer of heat through vibrations.
8. Reactivity: Covalent crystals generally have lower reactivity compared to ionic crystals. They do not readily undergo chemical reactions because the strong covalent bonds between atoms are stable and require high activation energy to break.
9. Lustrous Appearance: Many covalent crystals exhibit a lustrous or shiny appearance due to the regular arrangement of atoms and the reflection of light from their smooth surfaces.
10. Cleavage: Covalent crystals often exhibit cleavage planes, where the crystal can be split along specific planes of weakness. These planes of weakness occur when the covalent bonds are weaker in certain directions.
