Chains
One of the more important properties of carbon, from the point of view of organic chemistry, is its ability to "catenate" or form long chains with itself. Carbon is by no means unique in this regard as most of the non-metallic elements are capable of forming chains. However, carbon is unique in being able to form stable chains. That is, the structurally analogous silanes--mixtures of silicon and hydrogen--are spontaneously flammable in air.
Examples of simple chains are the hydrocarbons. In essence, these are built from the successive addition of -CH2 units.Methane is therefore one -CH2 inserted into a H-H bond. Ethane is two -CH2 units. Propane is three and so on.
Extension of these chains to the millionth -CH2 unit provides polymers and plastics. In essence, this is the basic structure of polyethylene.
Simple chains are not the only possibility. A variety of polymeric substances, built from repeating units, are also possible. But more important and interesting are the chains of life. These are the protein molecules, made from chains of amino acids strung together by amide bonds, and DNA/RNA, which are chains of nucleic acids strung together by phosphate linkages between the deoxyribose (for DNA) and ribose (for RNA) saccharides, respectively. Peptides, such as many human messengers and hormones, contain between about four to 100 amino acids. Proteins are longer chains, containing between 100-1,000 amino acids. DNA, on the other hand, is a chain of millions of base pairs. But in either case, it is the ability of carbon to form chains with itself that make these molecules possible.
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