Comparing Carbon-Carbon Bond in Graphite and Diamond

In this JC2 webinar we want to compare the bond energy of carbon-carbon bond in graphite and diamond.

The enthalpy of graphite is lower than that of diamond, which means that graphite is more stable than diamond.

This implies that the carbon-carbon bond in graphite is more stable than the carbon-carbon bond in diamond.

How is this possible if both are carbon-carbon single bonds?

Comparing Bond Energies using Hybridisation

Let's consider the state of hybridisation for carbon in graphite and diamond.

graphite and diamond deduce percentage s character

Carbon in graphite forms 3 sigma bonds with 3 other carbons hence it is sp2 hybridised. Its percentage s character is 1/3 or 33%.

Carbon in diamond forms 4 sigma bonds with 4 other carbons hence it is sp3 hybridised. Its percentage s character is 1/4 or 25%.

Since sp2 hybridised carbon in graphite has greater percentage s character, the sp2 orbitals will resemble more of s orbitals, hence it will be shorter and closer to the nucleus.

Therefore the corresponding bond formed from that shorter sp2 orbital will also be shorter and stronger.

So carbon-carbon bond in graphite will be more stable with a higher bond energy.

graphite and diamond sp2 carbon in graphite

Conversely, sp3 hybridised carbon in diamond has less s character, sp3 orbitals will resemble less of s orbital and more of p orbital, hence it will be longer and further away from the nucleus.

The corresponding bond formed from longer sp3 orbital will also be longer and weaker.

Hence carbon-carbon bond in diamond will be less stable with a lower bond energy.

graphite and diamond sp3 carbon in diamond

Topic: Introduction to Organic Chemistry, Organic Chemistry, A Level Chemistry, Singapore

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