The phenomenon by which an element can exist in more than one physical state is called allotropy.
Graphite is an allotrope of carbon which conducts electricity due to de-localisation of the electrons above and below the planes of the carbon atoms.
The carbon atoms in the Graphite structure are sp2 hybridized and are directed in the same plane thus forming hexagonal rings. The rings have many layers of particles. Graphite has a unique honeycomb layered structure. Each layer is composed of planar hexagonal rings of carbon atoms in which carbon-carbon bond length within the layer is 141.5 picometers.
Out of four carbon atoms three forms sigma bonds whereas the fourth carbon forms pi-bond. The layers in graphite are held together by Vander Waal forces.
Each carbon atom is bonded into its layer with three strong covalent bonds. This transmits each atom with a spare electron, which together form a delocalised ‘sea’ of electrons loosely bonding the layers together. These delocalised electrons can all move along together – making graphite a good electrical conductor.
Properties of Graphite:
- Since the layers are stacked over each other, this carbon allotrope can act as a lubricant.
- It also has metallic lustre which helps in the conduction of electricity. It is a very good conductor of both heat
- and electricity
- One of the most important properties of graphite is that it is used as a dry lubricant for machines at high temperature where we cannot use oil.
- Graphite is used to make crucibles which have the property that they are inert to dilute acids as well as to alkalis.