15.1    Introduction to Alkanes

What is an alkane?

• A hydrocarbon is a compound containing carbon and hydrogen atoms Examples of hydrocarbons are alkanes, alkenes, alkynes and arenes.

• Alkanes are saturated hydrocarbons, the carbon atoms are joined to each other via single covalent bond They form the homologous series with a general formula CnH2n+2.
• Physical properties of alkanes:
  1. Alkanes are non-polar, thus they are soluble in non-polar solvents like CCl4. They are, in general, insoluble and less dense than water
  2. The boiling point of straight-chain alkanes increases with the size of molecule. This is because the number of electrons in each molecule increases, resulting in the increased strength of van der Waals’. Thus more energy is required to break these forces
  3. For a branched alkane, it is more volatile and its boiling point is lower than its counterpart with the same number of carbon atoms. This is because they are more spherical and have a lower surface area. Thus less temporary dipoles can be set up and the van der Waals’ forces are weaker, less energy is required to overcome it
  4. The density of liquid alkanes increases slightly. The mass of each succeeding molecule increases but due to the increased strength of van der Waals’ forces, the molecules are more closer This results in higher ratio of mass/volume.

• Cycloalkanes are alkanes that joined up as a ring. The smallest possible cycloalkane is cyclopropane. Cycloalkanes have two hydrogen less than the corresponding straight-chai alkanes.