The important characteristic properties of electrovalent compounds may be summarized as follows:
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1. Ionic compounds consist of ions:
All ionic compounds consist of positively and negatively charged ions and not molecules. In the crystal of sodium chloride every sodium ion is surrounded by six evenly spaced chloride ions and vice versa in a regular fashion.
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Similarly, in potassium nitrate, the units of the crystal are the potassium and the nitrate ions.
2. Ionic compounds are solids:
Because of strong electrostatic attractions between ions, these are solids and relatively hard. But these compounds are generally brittle and break into pieces when pressure is applied.
3. Ionic compounds have high melt. pts and boil pts:
Due to the powerful electrostatic force between the ions in a crystal of an ionic/electrovalent compound, considerable energy is needed to overcome these forces and break down the crystalline lattice.
Hence these compounds possess high m. pts and b. pts.
4. Ionic compounds are generally soluble in water:
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Polar solvents like water weaken the interline attractions and break the lattice. Therefore, ions are dispersed and dissolve in water and are insoluble in non-polar solvents like kerosene, acetone, petrol, etc.
5. Ionic compounds conduct electricity in molten state or when dissolved in water:
When an electrovalent compound is melted or dissolved in water, the binding forces in the crystal disappear and the component ions become mobile and they conduct electricity.