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