A hydrocarbon is a compound whose elements consist of only Hydrogen and Carbon. They occur naturally in natural gas, coal, and petroleum(crude oil). Methane is a natural component of natural gas which we would talk more about in this article.
Hydrocarbons can be classified into two namely aliphatic and aromatic hydrocarbons. An aliphatic hydrocarbon is one in which the carbon atoms form either a straight or branched chain(alicyclic) or ring(cyclic). They are saturated if only single bonds exist between all the carbon atoms in the molecule and unsaturated if there exist multiple bonds between two adjacent carbon atoms.
Aromatic hydrocarbons are cyclic and highly unsaturated; the most common ones being benzene, naphthalene, and anthracene. These hydrocarbons can further be classified into alkanes, alkenes, alkynes, and others to mention a few.
Alkanes(Paraffins)
Alkanes are saturated aliphatic hydrocarbons that form homologous series with the general molecular formula CnH2n+2 (where n is a whole number 1, 2,3,4, etc). An alkane is any hydrocarbon having only single covalent bonds between adjacent carbon atoms.
IUPAC Nomeclature Of Alkanes
The Characteristic ending of the alkane is -ane. The first four homologous are called by their trivial names, while the names of the others are derived from Latin prefixes that indicate the number of carbon atoms per molecule. The table below outlines the IUPAC names and chemical symbols of the first ten alkanes.
| Molecular Formula | IUPAC Name |
| CH4 | Methane |
| C2H6 | Ethane |
| C3H8 | Propane |
| C4H10 | Butane |
| C5H12 | Pentane |
| C6H14 | Hexane |
| C7H16 | Heptane |
| C8H18 | Octane |
| C9H20 | Nonane |
| C10H22 | Decane |
Physical Properties Of Alkanes
The following are the physical properties of alkanes:
- Alkanes with 1 to 4 carbon atoms are colourless and odourless gases; those with 5 to 16 carbons are colourless liquids(paraffin oils); while the rest are amorphous waxy solids.
- They are non-polar; hence insoluble in water, but soluble in organic solvents, like benzene
- Their physical properties, such as boiling points, melting points, and density increases regularly as the number of carbon atoms per molecule increases. This is due to an increase in van der Waal’s forces of attraction between the molecules as the molecular mass increases.
Isomerism In Alkanes
Isomerism is the occurrence of two or more compounds with the same molecular formula but different structural formulae. Compounds that exhibit this are known as isomers. When two or more compounds differ in the arrangement of carbon atoms in their molecules, they are structural isomers[Alkanes with four or more carbon atoms exhibit structural isomers].
Alkyl
When one hydrogen atom in an alkane with the general formula CnH2n+2 is removed, an unstable alkyl group with the general formula CnH2n+1 is formed.
Uses Of Alkanes
The following are some of the uses of alkanes:
- Gaseous and liquid alkanes are useful sources of heat
- Halogenated alkanes like trichloromethane can be used to make anesthetic while triiodomethane can be used to make disinfectants.
Alkenes
Alkenes are also known as Olefins and they are unsaturated hydrocarbons that form homologous series with the general formula CnH2n (n starts from 2, then 3, 4,…). Unlike alkanes, alkenes start numbering from 2 and not 1. The table below outlines the IUPAC names of some alkenes and their molecular formula.
| Molecular Formula | IUPAC Name |
| C2H4 | Ethene |
| C3H6 | Propene |
| C4H8 | Butene |
| C5H10 | Pentene |
Physical Properties Of Alkenes
Below are some of the physical properties of Alkenes:
- Alkenes with 2 to 4 Carbons atoms are colorless gases; Those with 5 to 15 Carbon atoms are colourless liquids, while the others are waxy solids.
- Alkenes are insoluble in water due to their highly polar nature.
- Their melting and boiling points increase with an increase in relative molar mass.
- Cis-isomers of alkenes are unsymmetrical while trans-isomers are symmetrical about the double bond.
Uses Of Alkenes
- Alkenes are generally used as starting materials in the organic chemical industry.
- Ethes and propenes are sources of plastics, organic solvents, and detergents.
- Ethene is used in the production of ethanol; as a fuel; and in ripening fruits.
Alkynes(Acetylene)
The alkynes are unsaturated hydrocarbons that form homologous series with the general formula CnH2n-2 where n starts from 2. Alkynes are characterized by the presence of a triple covalent bond between two adjacent carbon atoms. The table below outlines the IUPAC names of some alkynes and their molecular formula.
| Molecular Formula | IUPAC Name |
| C2H2 | Ethyne |
| C3H4 | Propyne |
| C4H6 | Butyne |
| C5H8 | Pentyne |
Physical Properties Of Alkynes
- Alkynes with 2 to 4 carbon atoms are colourless and odourless gases(except ethyne which has a peculiar sweet odour). Those with 5 to 13 Carbon atoms are colourless liquids, while others are colourless solids.
- They burn with smoky luminous flame due to high carbon contents
- They have higher boiling points than the corresponding alkenes and alkanes.
- Their boiling and melting points increase with increasing molecular mass
Uses Of Alkynes
- A mixture of Oxygen and ethyne called Oxy–acetylene is used in welding.
- Ethyne is used in the production of polyethynlchloride(polivynl chloride, PVC) which is used in making floor tiles, and plastic pipes.