There are four types of solids:
1. Metallic: composed of only metal atoms and held together by metallic bonds. Electrons in metallic solids are delocalized, meaning that electrons move freely from atom to atom expanding the molecular oribitals across the whole solid. This is also called a sea of electrons. Since the electrons are delocalized metal nuclei can easily be moved as it does not take much energy to separate atoms. This is what makes metals malleable and ductile. The delocalization of electrons also makes metals excellent conductors. Metallic solids have a wide range of melting points.
2. Ionic: formed from a cation(metal atom) and anion(non-metal atom) bond interactions. Electrons are not delocalized like metallic solids instead they are localized around the anion. Ionic solids are not conductive in solid form but conduct a current in aqueous ion forms. Ionic solids have high melting points the higher the charge of the cation and anion the higher the melting point. Ionic solids are also brittle. Most ionic solids are soluble in water.
3. Network covalent: formed from the covalent bonding of the same atom/atoms throughout the solid. Network covalent solids are hard and have high melting points. Network covalent solids are not conductive.
4. Molecular (Vander walls solids): solids held together by dipole-dipole interactions. hydrogen bonding, and london dispersion forces. This is mostly done by liquids or gases at room temperature when they hit a low temperature forming solids. These solids have low melting points and are soft due to weak bond interactions. Most molecular solids are not soluble in water. Molecular solids are not conductive.
In the lab the properties used to classify the solids were melting point, conductive in solid form and in water solution, and soluble in water polar organic and non-polar organic solutions.
Based on these properties metallic will conduct and ionic, network covalent, and molecular solids will not conduct. Metallic solids will have varying melting points Ionic and network solids will have a high boiling point, and molecular will have low boiling points.
These are the results(Zinc is conductive as solid):
Citric acid: molecular CaCl2: ionic Sand:Network covalent Charcoal: network covalent