Question

Why is diamond hard and graphite brittle while both are made up of carbon atoms?

• A. Difference in the melting point
• B. Difference in the conductivity
• C. Difference in nature of carbon bonds
• D. Difference in the boiling point

Answer 1

The correct option is C Difference in nature of carbon bonds

Diamond and graphite are both made up of carbon atoms, except they have different physical form and properties, due to the nature of bonds formed between the carbon atoms.

In diamond, the 4 valence electrons of a carbon atom form covalent (sigma bonds) bonds with adjacent carbon atoms. It is the covalent bond that gives a diamond its strength. In graphite, 3 valence electrons of a carbon atom form covalent bonds (sigma bonds) with adjacent carbon atoms.

The layers are held together by weak van der Waals forces that make graphite soft.

So, the correct option is $C$