Amorphous solids are formed when liquids are cooled too quickly from the molten state to allow the sub-units to arrange themselves in the low energy, crystalline state. Solids with pure ionic bonds do not form amorphous solids but all the other bond types can produce amorphous solids. The tetrahedral SiO 2 structure forms the sub-unit, and it is the flexibility of the corner to corner links that accounts for the ability of SiO 2 to form random structures. If the molten Sillica is cooled very slowly, then the sub-units fall into the regular crystal structure of Quartz. Impurities in SiO 2 hinder crystallisation.
Polymers have long chains of carbon atoms with side groups.
The bonds between the backbone carbon atoms and the side groups are covalent. Waal's bonds means loose packing. The most common polymer is polyethylene , which has only hydrogen atoms are attached to its carbon chain. The more branches a polymer has, the greater the tendency for the polymer to be in the amorphous state. Important branched polymers are polyethylene and polypropylene .