Question

Diamond is hard because:
(a) all the four valence electrons are bonded to each carbon atoms by covalent bonds
(b) it is a giant molecule
(c) it is made up of carbon atoms
(d) it cannot be burnt

Answer 1

Hint: Generally carbon has valency four. So, it is good to make covalent bonds. Diamond has only carbon in it.

Complete step by step solution:
-Diamond is a solid form of carbon. It is an allotrope of carbon. It has a crystal structure called diamond cubic.
-The carbon in diamond is \[s{{p}^{3}}\]hybridised. That is, all the four valence electrons are involved in covalent bond formation with other carbon atoms. It has a tetrahedral structure. This makes it very strong.
Therefore, the correct answer for the question is option (a).

Additional Information:
- Arrangement of atoms is very rigid; because of this any little impurity present can contaminate it and can cause small variation in its properties.
- Synthetic diamonds are grown from high purity carbon under high pressure and temperature of hydrocarbons gas.
- Crystal structure of diamond is called diamond cubic. Its unit cells are stacked together.
- A diamond cubic lattice consists of two interpenetrating face-centered cubic lattices.
- Due to its hardness, it has wide industrial applications. It is used for cutting and polishing tools.
- It is also a gemstone. Pure diamond does not conduct electricity. These are excellent insulators. But a blue diamond (diamond with certain impurity) is a semiconductor.
- Diamond is lipophilic and hydrophobic in nature. The surface of it is partially oxidised.
- At room temperature, diamonds do not react with any chemical reagents such as strong acids and bases. But by igniting diamond at a very high temperature in the presence of oxygen, it combusts to carbon dioxide and water.

Note: Covalent bonds are actually weaker than ionic bonds. Still diamond which has only covalent bonds between its carbon atoms is the hardest substance. This is because of its tetrahedral structure.