Physical properties of Alkanes

Boiling and melting points- Alkanes are covalent compounds which consist of simple molecules. These molecules are held by weak van der waals forces. Hence. alkanes generally have low melting and boiling points.

However, as the molecules become larger, there is a gradual increase in the melting and boiling points. The surface area of the molecule as well as the number of electrons surrounding the molecule increases as the size of the molecule increases. This leads to a stronger van der waals force. Larger energy is required to overcome the stronger van der waals force between the molecules.

Density- Alkanes are less dense than water/ They form a colourless oily layer floating on top of water. The densities of the alkanes increase gradually with increasing molecular mass.

Viscosity- The alkanes become more viscous as their molecular size increase. This is because the van der waals force are stronger as the alkane molecules become bigger. This makes it difficult for the liquid to flow.

Solubility- Alkanes are insoluble in water, but are soluble in organic solvents such as ether.

Electrical conductivity- Alkanes are simple covalent molecules. The absence of mobile ions makes them unable to conduct electricity.

Flammability- As the molecular size of the alkane molecules increases, the percentage of carbon in the alkane molecules also increases. As a result, alkanes become less flammable. They also produce a smokier flame due to the incomplete combustion of alkane molecules.