Write a note on covalent or network solids.

(N/A) - These solids are also known as giant molecules. They consist of atoms held together by covalent bonds throughout the crystal.
- The covalent bonds are strong and directional in nature,which holds the atoms very strongly at their positions.
- These solids are very hard and brittle. They have extremely high melting points and may decompose before melting.
- They are electrical insulators and do not conduct electricity. Examples include diamond and silicon carbide $(SiC)$.
- Graphite is an exception; it is soft and a good conductor of electricity.
- In graphite,each carbon atom is covalently bonded to three neighboring carbon atoms in the same layer,leaving the fourth valence electron free to move between layers,which makes graphite a good conductor.
- Since the layers in graphite can slide over each other,it is a soft solid and acts as a good solid lubricant.