Final answer:
Diamond is an insulator because each carbon is covalently bonded to four other carbons, leaving no free electrons for conduction. Graphite is a semimetal due to its layered structure with delocalized π electrons in each layer, allowing electrical conductivity within the planes, while weak interlayer forces facilitate layer sliding.
Step-by-step explanation:
The differences in bonding between diamond and graphite lead to their distinct electrical properties, with diamond being an insulator and graphite being a semimetal. Diamond consists of a three-dimensional crystal lattice where each carbon atom is covalently bonded to four other carbon atoms, sharing electrons in a very strong bond that holds the structure together tightly. This tight bonding leaves no free electrons available for electrical conduction, making diamond a good insulator.
Graphite, on the other hand, has a layered structure. Within each layer, carbon atoms are bonded in a hexagonal pattern with strong covalent bonds, similar to those in benzene, resulting in a net carbon-carbon bond order of 1.33. Each carbon atom forms three covalent bonds within the layer, with one unhybridized p-orbital electron that can move about freely. These free-moving p electrons provide a path for electrical conductivity within the planes, while the weak interlayer London dispersion forces allow the layers to slide over each other. Thus, graphite exhibits properties of both covalent and molecular solids, being a good conductor within the planes of carbon atoms due to delocalized π bonding.
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