Key concepts in chemistry Study Guide

Fullerenes are allotropes of carbon, meaning they are different structural forms of the same element. Two notable examples are Buckminsterfullerene (C60) and graphene. Their unique properties stem directly from their distinct structures and bonding. C60 is a spherical molecule composed of 60 carbon atoms arranged in pentagonal and hexagonal rings, resembling a football. Each carbon atom in C60 is covalently bonded to three other carbon atoms, resulting in strong covalent bonds within the molecule. However, between C60 molecules, only weak intermolecular forces exist. This gives C60 properties such as being a soft solid with a relatively low melting point, and being a poor conductor of electricity due to localised electrons within the covalent bonds. Graphene, on the other hand, is a single layer of carbon atoms arranged in a hexagonal lattice. It can be thought of as a single layer of graphite. Each carbon atom is covalently bonded to three other carbon atoms, forming extremely strong covalent bonds within the layer. These strong bonds, combined with its two-dimensional structure, make graphene incredibly strong and lightweight. Unlike C60, graphene possesses delocalised electrons across its entire structure. These delocalised electrons are free to move, making graphene an excellent conductor of electricity and heat. Its high surface area and chemical inertness also contribute to its potential for diverse applications.

Simple polymers are large molecules, specifically macromolecules, formed by the joining together of many small, identical repeating units called monomers. This process is known as polymerisation. A common example is poly(ethene), which is formed from ethene monomers. Each ethene molecule (C₂H₄) contains a carbon-carbon double bond. During polymerisation, this double bond breaks, allowing the ethene units to link together in long chains. The resulting poly(ethene) molecule consists of thousands of carbon atoms linked end-to-end, with hydrogen atoms attached along these chains. These long chain structures give polymers their characteristic properties, such as flexibility and strength, making them useful in many applications, from plastic bags to pipes.