Q. What are the physical properties of solids?

Ans.

Most solids eventually melt when heated. This is because the particles gain enough energy to exceed the attractive forces which hold them in their fixed lattice positions. The normal melting point of a crystal is the temperature at which it melts under 1 atm pressure.

The four types of solids are ionic solids, molecular solids, metallic solids, and covalent network solids:

• Ionic Solids. The attractive forces between oppositely charged ions in an ionic solid are very strong. Therefore, ionic solids have very high melting points.

• Molecular Solids. Molecular crystals (such as sulfur) are usually held together by weak electrical forces. These solids therefore have lower melting points than ionic solids.
• Metallic Solids. Metallic solids are good electrical conductors because of the sea of electrons which are free to move throughout the solid. 
• Covalent Network Solids. These solids are held together by a network of directional covalent bonds. The entire network can be considered one giant molecule! The atoms of covalent network solids are hard to break up. Their melting points are very high. Diamond, a form of carbon, is an example of a covalent network solid.