How do ionic and molecular compounds compare in terms of physical properties?
You can usually differentiate them in terms of boiling point and solubility in water.
Under standard conditions, only structures such as diamond (structures that involve silicon) will have higher boiling point/melting point than ionic compounds. Other than that, covalent compounds have lower boiling point/melting point than ioninc compounds.
Ionic compounds are able to dissolve in water to form ions hence able to conduct electricity as the ions are able to carry charges.
Covalent compounds are usually not able to dissolve in water as not all of them have hydrogen bonding in the molecule. For example hydrogen chloride. Hydrogen chloride molecule has 2 hydrogen bond. Hydrogen atom forms partial positivity while chlorine forms partial negativity. The chlorine has non bonding electrons which allow it to form bonds with the oxygen atom in water. Hence hydrogen chloride is able to dissociate in water to form hydrogen ion and chloride ion. In other words, the hydrogen chloride molecule has dissolved in water.