Fundamentals

Question 1

Describe inter-molecular/ van der Waal forces.

Answer 1

Molecules in covalent compounds can have fluctuating charges. These are called fluctuating dipoles and they create small forces which partially bind materials together.
These secondary bonds are relatively weak and have the strength of about 1% of a primary bond.

Question 2

What is a polymer?

Answer 2

A solid composed of long molecular chains which are formed by linking shorter chain molecules (monomers).

Question 3

Compare Addition and Condensation Polymerisation.

Answer 3

Addition: Two or more monomers of the same type are linked in a larger molecule. No change in chemical composition, as they retain their original properties, and no by-products formed. eg polyethylene

Condensation: Two or more monomers of different types react together to form a polymer with a by-product, or ‘split off’ component (normally water). eg bakelite

Question 4

Compare homopolymers to copolymers.

Answer 4

Homo: ‘the same’. One monomer to form a polymer in a chain. eg ⚫️⚫️⚫️⚫️⚫️⚫️

Co: combining two or more monomers to form a polymer in a chain. Can be in different forms, but eg 🔘🔘⚫️🔘

Question 5

Compare thermosoftening polymer (thermoplastic) with thermosetting polymers.

Answer 5

Both have a web like structure with bonds interlinking the molecules.

Thermosoftening:
Along the chains, the links are primary bonds which are strong, but the ones between the chains are secondary bonds which are much weaker (these use van der Waal’s forces, among others).

If the plastic is heated, the secondary bonds weaken and the molecules can easily move about, allowing the polymer to be reshaped. These retain their new shape when cooled and can be re-heated and re-softened many times before it affects the strength of the polymer. eg polycarbonate (PC).

Thermosetting:
The main difference between the two is that where thermoplastics have secondary bonds, thermosetting polymers have cross-links. These are much stronger and don’t allow molecules to move around freely, meaning the polymer cannot be reheated once formed without charring or decomposition occurring. Generally stronger. eg epoxy resins (kevlar)

Question 6

What are the different types of ceramics and their properties?

Answer 6

Clay body:
Produced by moulding wet clay to the required shape. Structure is solid particles in a glassy matrix. Low porosity (less than 1%) which is essential to retain water (eg porcelain in toilets)

Glass:
These are the most widely used ceramics. They have been cooled to rigidity without crystallisation, and are therefore amorphous. They are durable, can withstand sudden temperature change, moderate impact resistance. eg ceramic cooktops or gorilla glass