Why is diamond hard & graphite soft?

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Solution

Diamond and graphite show different properties because of difference in their structure.

Diamond

Graphite (blue dots represent carbon atoms)

If you look closely, you will find that every carbon atom in diamond is bonded to 4 other carbon atoms via 4 valence electrons of carbon. Whereas in graphite every carbon atom is bonded to only 3 other carbon atoms via 3 valence electrons, leaving 1 free electron in graphite per carbon atom. Due to the rigid strongly bonded three-dimensional structure of diamond, diamond is hard in nature.
Now, apart from that, you will find that in graphite, the hexagonal ring structure consists of carbon atoms bonded by covalent bonds whereas longer and weaker Vander Waals bonds exist between two hexagonal rings. Due to these weak Vander Waals bonds, the rings can slip over each other thus making graphite soft

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Similar questions

Q. Why diamond is a hard and the graphite is very soft.

Q. Assertion :Graphite is soft while diamond is hard. Reason: Graphite has three dimensional structure while diamond has planner.

Q. Assertion :Graphite is soft while diamond is hard. Reason: Graphite has three dimensional structure while diamond has planar structure.

Q. Assertion (A): Graphite is a good conductor of electricity, however, diamond belongs to the category of insulators. Reason (R): Graphite is soft in nature on the other hand diamond is very hard and brittle

(a) What is the unique property of carbon atom? How is this property helpful to us?
(b) Explain why diamond is hard while graphite is soft (though both are made of carbon atoms).

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