Plastics are comprised of a combination of elements such as carbon, silicon, nitrogen, oxygen, sulfur, chlorine and hydrogen. Carbon atoms form the backbone of most plastics, except the silicones, which have silicon as their base element. Plastics are polymers.
Plastics generally consist of molecules made up thousands of atoms bound to each other. As a result, most plastics have a high molecular weight. In carbon-based plastics, each carbon atom can join with other atoms and create up to four chemical bonds. These can result in long chains, forming a thermoplastic. Examples of plastics in general use include the packaging of cleaning products, car bumpers and the packaging of food products, such as ketchup.