Properties of Hydrocarbons

Hydrocarbons are compounds that are made up of only hydrogen and carbon atoms. The number of atoms within the compound can affect the structure and properties of the hydrocarbons.

Understanding the basics of hydrocarbons is important for organic chemistry, as they are a fundamental component of crude oil.

Hydrocarbons are an incredibly diverse group, so categorising them outside of a few basic properties can be quite complex. However, some of the key features of hydrocarbons include:

  • Boiling point
  • Viscosity
  • Flammability

Boiling point

The boiling point is the temperature at which a liquid turns to gas.

As hydrocarbon molecules get larger, the boiling point increases because there are greater intermolecular forces between larger hydrocarbons. This is due to an increase in the number of electrons in the molecule and a greater surface area. Therefore, it requires more heat energy to break these forces of attraction.

  • For example, ethane (C2H6) has a boiling point of -89 °C, while heptane (C7H16) has a boiling point of 98 °C


Viscosity is a measure of a liquid’s resistance to flow, or its thickness. A highly viscous liquid tends to be thick and does not flow easily, whereas a liquid with low viscosity is runny, so it flows more easily.

As the size of the hydrocarbon increases, its viscosity also increases. This is due to the increasing intermolecular forces of attraction between the molecules.


Flammability tells us how easily a hydrocarbon combusts. Smaller hydrocarbons are much more flammable than larger hydrocarbons, so they are very effective as fuels, releasing large amounts of energy.

As the hydrocarbons increase in size, they become less flammable.