The simplest class of organic compounds is hydrocarbons (compounds consisting of only carbon and hydrogen elements). Carbon is the only element capable of forming stable, extended chains of atoms bonded through single, double, or triple bonds. Hydrocarbons are divided into four general classes, depending upon the nature of bonds present in their molecules. These are alkanes, alkenes, alkynes and aromatics. Each carbon atom of a hydrocarbon has four bonds.
Hydrocarbons are further classified as saturated and unsaturated. The members of these classes have different chemical properties because of different nature of bonds present in them. However, their physical properties are similar because of comparable electronegativities of carbon and hydrogen. Thus, they are almost nonpolar and insoluble in water. They dissolve readily in non polar solvents. They are gases or volatile liquids and their volatility decreases with the increase of molecular mass. That is the reason low molecular mass hydrocarbons are gases at room temperature, such as: and . Moderate molecular mass hydrocarbons are liquids, such as, , while higher molecular mass hydrocarbons are solids.
Fossil fuels are hydrocarbons. They are not only major sources of energy but also are raw materials used to make thousands of consumer products. Hydrocarbons are the starting materials for the synthesis of organic chemicals of commercial importance. These chemicals are essential for making plastics, synthetic rubbers, synthetic fibres and fertilizers, etc.
Hydrocarbons are those compounds which are made up of only carbon and hydrogen elements. Hydrocarbons are regarded as the parent organic compounds since other organic compounds are considered to be derived from them by the replacement of one or more hydrogen atoms by other atoms or group of atoms.
Types of Hydrocarbons
On the basis of structure, hydrocarbons are divided into two main classes:
(i) Open chain or Aliphatic hydrocarbons: These are the compounds in which the first and the last carbon are not directly joined to each other. The open chains of carbon may be straight or branched.
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Types of open chain hydrocarbons
Open chain hydrocarbons have been further subdivided into saturated and unsaturated hydrocarbons.
(a) Saturated hydrocarbons
The hydrocarbon in which all the four valencies of carbon atoms are fully satisfied (saturated) by single bonds with other carbon atoms and hydrogen atoms are called saturated hydrocarbons. Saturated hydrocarbons are also called alkanes. Thus, an alkane is a hydrocarbon in which the carbon atoms are connected by only single covalent bond (there are no double or triple covalent bonds in alkanes).
Methane , ethane , propane and butane are all saturated hydrocarbons because they contain only carbon- carbon single bonds, as shown below: