Graphite is an allotrope of carbon
a) Define the term Allotrope
b) Describe the structure and bonding in graphite and explain why graphite is used as pencil lead and conduct electricity.
a) Allotrope refers to one of two or more different forms of an element that exist in the same physical state but differ in their chemical and physical properties.
b) In graphite, each carbon atom is bonded to three other carbon atoms in a hexagonal planar array, forming layers of flat sheets. The layers are held together by weak van der Waals forces, allowing the sheets to slide over one another, making graphite soft and slippery. Each carbon atom in graphite also has one delocalized pi electron that can move along the layers, making graphite conductive.
The structure of graphite also explains why it is used as pencil lead. When graphite is rubbed onto paper, the weak van der Waals forces between the layers are broken and the sheets slide off onto the paper, leaving a mark.
In summary, the unique structure and bonding of graphite makes it an excellent conductor of electricity and also allows for its use in writing materials such as pencil lead.