Graphite: structure, bonding and physical properties
Bonding, structure, and the properties of matter • Structure and bonding of carbon
Flashcards
Test your knowledge with interactive flashcards
Key concepts
What you'll likely be quizzed about
Atomic arrangement and layer structure
Graphite has a two-dimensional arrangement of carbon atoms in hexagonal rings that form flat sheets. Each sheet is called a layer and layers stack in parallel to create the bulk material. The layers show regular repeating hexagons with carbon atoms at the vertices, producing a planar lattice with a defined spacing between layers. Layer stacking produces anisotropy in physical properties: strong bonding exists within sheets, while weak attractions between sheets allow different behaviour parallel and perpendicular to the layers. The layer spacing limits interlayer interactions and determines how easily layers slide.
Bonding within layers (sp2 hybridisation)
Each carbon atom in a graphite layer forms three sigma (σ) covalent bonds to neighbouring carbons using sp2 hybrid orbitals. The three sigma bonds lie in the plane of the layer and create strong, rigid connections between atoms. The planar geometry enforces 120° bond angles and a hexagonal ring structure. One unhybridised p orbital remains on each carbon atom and overlaps with p orbitals on adjacent carbons to form pi (π) molecular orbitals. The sigma framework gives graphite high thermal stability and a high melting point because large energy is required to break the in-plane covalent bonds.
Delocalised electrons and electrical conductivity
The unhybridised p orbitals combine across each layer to form a system of delocalised electrons (pi electron cloud) that extends over the whole sheet. These delocalised electrons move freely within the plane of the layers and carry electrical charge. Delocalisation causes electrical conductivity parallel to the layers because electrons can flow along the pi system. Conductivity perpendicular to the layers is low because electrons cannot easily move between separate sheets due to weak interlayer forces.
Interlayer forces and lubricating behaviour
Adjacent graphite layers interact through weak van der Waals forces or London dispersion forces. These forces are much weaker than the covalent bonds within layers and allow layers to slide past each other under applied stress. Layer sliding produces a low-friction surface and explains graphite's use as a dry lubricant and its characteristic softness. The ease of shear depends on the strength of the weak interlayer attractions and the presence of impurities or adsorbed species between layers.
Macroscopic properties derived from structure
Strong covalent bonding within layers causes graphite to have a very high melting point and thermal stability, because breaking many strong bonds requires large energy input. The delocalised electrons produce electrical conductivity and thermal conduction along layers. The combination of strong in-plane bonds and weak interlayer forces produces material properties that are direction-dependent: high strength and conductivity within layers, softness and lubricity perpendicular to applied shear, and chemical inertness that leads to insolubility in common solvents.
Key notes
Important points to keep in mind