Why is diamond so strong?

Answer: Each carbon atom in a diamond contains four electrons in its outer shell, and for addition of carbon atoms share these electrons through covalent interactions.

• A solid tetrahedral crystal is produced with the aid of this structure. One of the hardest earth materials, diamond is one of the tightly-bonded nanostructures. 
• As a result, each carbon atom is connected to four of its neighbours. Creating a solid tetrahedral structure as a result. Diamond is the hardest material because of its tight bonds.