【Daily Question】Theoretical Foundation 2020.07.17
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Multiple-choice question: The reason why graphite can conduct electricity is that in graphite crystals ( ) A. there are free electrons within the layers; B. there are hybridized orbitals within the layers; C. it belongs to a metallic crystal structure; D. there are delocalized π bonds within the layers. Answer: D. Hint: Those who can explain the reasoning behind the solution will receive an additional reward; the answer can be found in the response
D. Delocalized large л bonds exist within the layer
Delocalized large л bonds exist within the layers. Exclusion principle: Graphite is a molecular crystal; it has no free electrons, and hybrid orbitals are merely a theoretical concept – they do not represent the existence of hybrid orbitals in the molecule.
Reason D: Graphite crystals have a layered structure, and the lattice particles of graphite contain three different types of bonds (covalent bonds, van der Waals forces, and metallic bonds). The carbon atoms in the same layer use sp2 hybridized orbitals to form σ bonds with other carbon atoms, creating a hexagonal, honeycomb-like layered structure. The bonds between carbon atoms are very strong and difficult to break; as a result, graphite has a high melting point and very stable chemical properties. Furthermore, each carbon atom has p orbitals that are perpendicular to the plane of each layer, and these p orbitals are parallel to one another. These p electrons can form delocalized π bonds over relatively large distances, held together by weak van der Waals forces; as a result, the layers can slide easily past one another, which is what gives graphite its slippery texture. Furthermore, since the delocalized electrons in the π bonds can move along the plane of the layers, graphite exhibits a metallic luster and is capable of conducting heat and electricity. Each layer of graphite contains a large pi bond, which allows the electrons in that layer to share and move freely, thereby enabling conductivity. However, its electrical conductivity is poor in the vertical direction.