Carbon
Plastic is made of monomers. Organic plastics are polymers, composed of monomers (repeating units). A polymer is a chain of molecules repeated again and again. Plastics are made of many repeating units of monomers to form a long chain known as a polymer. Different types of plastics have different monomers. Examples of polymers that … are plastics include polyvinyl chloride (PVC) and polystyrene. Synthesis means that something is put together, and synthetic materials are made of building blocks that are put together in factories. The building blocks for making plastics are small organic molecules-molecules that contain carbon along with other substances. When you polymerize ethylene you get a polyethylene resin. There are a number of polyethylene resins families that differ by such properties as density and molecular weight, and they can be made into a huge variety of plastic products. One of the most common is the plastic grocery bag. Polyethylene is made from just ethylene monomers-but it's also possible to create polymers from two or more different monomers. You can make hundreds of different polymers depending on which monomers and catalysts you use Plastics are derived from organic products. The materials used in the production of plastics are natural products such as cellulose, coal, natural gas, salt and, of course, crude oil. Crude oil is a complex mixture of thousands of compounds. To become useful, it must be processed. The distillation process involves the separation of heavy crude oil into lighter groups called fractions. Each fraction is a mixture of hydrocarbon chains (chemical compounds made up of carbon and hydrogen), which differ in terms of the size and structure of their molecules. One of these fractions, naphtha, is the crucial element for the production of plastics Plastic bags are made out of non-biodegradable substance.(not organic)Because they are durable they do not rot. Scientist believe that it would take up to 1,000 years to break … down. In that time plastic bags separate into smaller toxic particles that contaminates the soil and even waterways. That means that 1 million plastic bags are made each minute, but then billions end up as litter each year. Making plastic bags can lead to exhaustion of oil, because to make a lot of plastic bags, we need a lot of oil. If we reduce oil we could save much more oil. Today people can make new kinds of molecules in laboratories and factories. Some of the biggest molecules that people make are plastics, like what plastic garbage bags or plastic Legos are made of. Plastics are also hydro-carbon molecules. People also make new molecules for medicines. Protein molecules-each dot is one molecule. A molecule is a group of two or more Atoms that stick together. Molecules (MOLL-uh-cyools) are so small that nobody can see them, except with an electron microscope. Pretty much everything on Earth and other planets is made of molecules, and so is some of the dust in space. What are plastic bags made out of? Plastic refers to different materials made from carbon (which is usually drawn from petroleum), used in anything from milk jugs to vinyl jackets. Household products, including shopping bags, are typically printed with a number to make sorting and recycling easier. Bags also end up in waterways and, eventually, the ocean, choking and killing wildlife along the way. An estimated 80 percent of the giant swirling soup of trash known as the Great Pacific Garbage Patch is made up of plastic particles, mostly from shopping bags. Plastic Bags About Plastic Bags Plastic bags are all around us – we use them for shopping, carrying and storing, disposing of rubbish and more. Australians use about 3.9 billion i lightweight supermarket shopping bags every year. There are two major types of plastic shopping bags. Lightweight, checkout-style bags are most commonly found in supermarkets and takeaway stores, and are made from high density polyethylene or HDPE. The heavier, tougher plastic bags found in boutique and department stores are made from low density polyethylene or LDPE. 
http://www.answers.com/Q/What_is_plastic_made_of http://www.nobelprize.org/educational/chemistry/plastics/readmore.html http://www.plasticseurope.org/what-is-plastic/how-plastic-is-made.aspx http://www.answers.com/Q/What_are_the_elements_that_make_up_a_plastic_bag http://quatr.us/chemistry/atoms/molecules.htm http://www.chicagoreader.com/chicago/what-are-plastic-bags-made-out-of/Content?oid=1110103 http://recyclingnearyou.com.au/documents/doc-716-plastic-bags-factsheet.pdf
what molecules are plastic bags made up of