Question

Graphite has a layered structure consisting of fused six-membered rings and is conducting at reasonable temperatures. Why would you expect diamond to be insulating?

Short answer

Diamond is expected to be an insulator because it has a different crystal structure from graphite. All of the outer shell electrons in diamond are involved in covalent bonds, leaving no free electrons available to conduct electricity.

Step-by-step solution

Understanding the Structure of Graphite and Diamond

Graphite consists of layers of carbon atoms, with each atom bonded to three others in a hexagonal arrangement, forming layers of hexagonal rings. The fourth outer shell electron of each atom is not used in the bonding and is free to move throughout the layers, enabling graphite to conduct electricity. However, in diamond, each carbon atom is bonded to four other carbon atoms in a tetrahedral structure. This rigid configuration results in a structure with each atom's electrons locked into the bonds, with none free to move around and conduct electricity.

Comparing Electrical Conductivity

Because all of diamond's outer shell electrons are engaged in bonding, there are no free electrons to participate in electrical conduction. Therefore, you would expect diamond, despite being an allotrope of carbon like graphite, to be an insulator rather than a conductor.

Conclusion

The difference in electrical properties between diamond and graphite lies in their unique crystal structures and bonding. Because graphite's structure leaves free electrons that can move and conduct electricity, it behaves as a conductor. In contrast, diamond's structure leads to all electrons being tightly bound and therefore provides no free electrons for electric current, making diamond an insulator.