Question

Diamond is hard but graphite is soft and slippery. Explain why?

Answer 1

Diamond is hard due to the presence of strong covalent bonds. Whereas, Graphite is soft and slippery due to the presence of weak Van der Waals forces.

Complete step by step solution:
Diamond is one of the most complex substances known and it has a density which is equal to $3.5gram.m{l^{ - 1}}$. Whereas, Graphite is soft and slippery and it has a density which is equal to $2.3gram.m{l^{ - 1}}$. We can clearly notice that graphite is less dense as compared to diamond which makes it soft and slippery.
We also all know that carbon is present in both diamond and graphite. Diamond is harder than graphite because each of its carbon atoms form four covalent bonds in a tetrahedral structure and also due to the presence of strong covalent bonds in it.
A chemical bond involving the exchange of electron pairs between atoms is known as a covalent bond.
Each of the carbon atoms in graphite, on the other hand, forms four covalent bonds in a hexagonal structure. The carbon atoms in graphite appear to bond with weaker intermolecular forces, allowing the layers to move over one another. The weak intermolecular forces are known as the weak Van der Waals forces.
Therefore, diamond is hard but graphite is soft and slippery even though both have carbon present in them.

Note: Amorphous, graphite, and diamond are three distinct allotropes of carbon that can be found on Earth. Allotropes are materials made of the same substance but with different atomic arrangements. Every carbon allotrope has its own set of physical properties.