The methylene group is the divalent group:CH₂. It is a modifier of the behavior of the functional group of a compound. This group of atoms is unsaturated and it is incapable of an independent existence due to the fact that other atoms will readily react with it. This is because the group has two potential chemical bonds unused and is, as a result, very reactive. The methylene group is often found in the central part of other organic molecules acting as a joining molecule for several other groups such as alkyl or aryl groups. It is often formed as an intermediate in organic reactions. For example, in the substitution reactions of alkanes, such as the chlorination of methane, methylene dichloride is formed (CH₂Cl₂).