In ionic solids, there are strong, electrostatic attractive forces between the positive and negative ions. To melt the solid, these very strong forces must be overcome. Thus all ionic compounds are solids at room temperature and generally they have very high melting and boiling points.
E.g. MgF2 has a melting point of. 1261°C and a boiling point of 2239°C
The strong forces between the ions are hard to break, and this also explains the fact that crystals of ionic compounds are hard. . Ionic substances form giant ionic lattices containing oppositely charged ions. They have high melting and boiling points, and conduct electricity when melted or dissolved in water. However, if a force is applied suddenly to the crystal, the layers of ions slip over each other:
Now, instead of a positive ion being over a negative one, it is over another positive one – which causes the layers to repel one another. So when a crystal is hit, it breaks apart very easily – it shatters. Thus ionic crystals are brittle. Ionic compounds formed from ions. Ions are created when a metal loses electrons and a non-metal gains electrons
