Doping is not a chemical process that needs to be understood in depth in Level 2 Chemistry. However, a basic understanding of this process will help explain and discuss the properties, uses and developments of polyacetylene.
Doping is a chemical process that adds or removes electrons, changing the conductive properties of a substance (making it a better electrical conductor). It is much like rubbing a plastic ruler (or rod) with a cloth, except that the change is more long-lasting.
Doping usually involves one of two chemical processes:
OXIDATION: loss of electrons/removal of electrons
REDUCTION: gain of electrons/addition of electrons
The removal of electrons works by "making space" for electrons from a power source.
The addition of electrons works by overloading each atom with electrons. These electrons go into higher energy levels, so are easily "moved on" to the next atom by electrons from a power source.
In Level 2 chemistry, you are not expected to understand "pi bonds" or "conjugated systems". However, a basic knowledge of these will help you explain and discuss the structure, properties and development of polyacetylene.
PI BONDS
Alkenes and alkynes have a type of bond between the carbon atoms called a "pi bond".
The first bond between the carbon atoms is called a "sigma bond" and it holds the carbon chain together.
The next bond formed between the same two carbon atoms is called a "pi bond". It is not as strong as a sigma bond, but it is what prevents rotation of the double (or triple) bond.
Alkenes have one pi bond per carbon-carbon double bond (as well as one sigma bond).
Alkynes have two pi bonds per carbon-carbon triple bond (as well as one sigma bond).
We need to understand pi bonds to understand the next concept (conjugated systems).
CONJUGATED SYSTEMS
When a molecule has alternating single and double bonds, we call this a conjugated system. This means it also has a "layer" of pi bonds, usually drawn above and/or below the sigma bonds.
In cyclic compounds (such as benzene, shown in the video), this is represented as a circle inside the cyclic structure. We do not do the same thing with non-cyclic substances (such as polymers), but we need to keep in mind that the entire structure "shares" these bonding electrons.
A polymer with conjugation will allow for movement of these pi bond electrons You need to link this key idea to the properties and (proposed) uses of such a polymer.
