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Hydrocarbons

Compounds containing only carbon and hydrogen, their properties and classification.

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Hydrocarbons

Look at all of the pictures above. Each one shows an item that you might have used or seen used by someone else. All of the items have something in common. Can you guess what it is? They all involve carbon compounds known as hydrocarbons.

What Are Hydrocarbons?

Hydrocarbons are compounds that contain only carbon and hydrogen. Hydrocarbons are the simplest type of carbon-based compounds, but they can vary greatly in size. The smallest hydrocarbons have just one or two carbon atoms. The largest hydrocarbons may have thousands of carbon atoms.

Q: How are hydrocarbons involved in each of the photos pictured above?

A: The main ingredient of mothballs is the hydrocarbon naphthalene. The main ingredient in nail polish remover is the hydrocarbon acetone. The lawn mower runs on a mixture of hydrocarbons called gasoline, and the camp stove burns a hydrocarbon fuel named isobutane.

Properties of Hydrocarbons

The size of hydrocarbon molecules influences their properties, including their melting and boiling points. As a result, some hydrocarbons are gases at room temperature, while others are liquids or solids. Hydrocarbons are generally nonpolar, which means that their molecules do not have oppositely charged sides. Therefore, they do not dissolve in water, which is a polar compound. In fact, hydrocarbons tend to repel water. That’s why they are used in floor wax and similar products.

Classes of Hydrocarbons

Hydrocarbons are placed in two different classes: saturated hydrocarbons and unsaturated hydrocarbons. This classification is based on the number of bonds between carbon atoms.

  • Saturated hydrocarbons have only single bonds between carbon atoms, so the carbon atoms are bonded to as many hydrogen atoms as possible. In other words, they are saturated with hydrogen atoms.
  • Unsaturated hydrocarbons have at least one double or triple bond between carbon atoms, so the carbon atoms are not bonded to as many hydrogen atoms as possible. In other words, they are unsaturated with hydrogen atoms.

Uses of Hydrocarbons

It is hard to overstate the importance of hydrocarbons to modern life. Hydrocarbons have even been called the “driving force of western civilization.” You saw some ways they are used in the opening image. Several other ways are pictured in the Figure below. The most important use of hydrocarbons is for fuel. Gasoline, natural gas, fuel oil, diesel fuel, jet fuel, coal, kerosene, and propane are just some of the commonly used hydrocarbon fuels. Hydrocarbons are also used to make things, including plastics and synthetic fabrics such as polyester.

Uses for hydrocarbons

Motor oil: Motor oil consists of several hydrocarbons. It lubricates the moving parts of car engines. Asphalt: Asphalt pavement on highways is made of hydrocarbons found in petroleum. Candle: Many candles are made of paraffin wax, a solid mixture of hydrocarbons. Lighter: This lighter burns the hydrocarbon named butane. Rain Boots: These rain boots are made of a mixture of several hydrocarbons. Transportation: These forms of transportation are fueled by different mixtures of hydrocarbons.

Sources of Hydrocarbons

The main source of hydrocarbons is fossil fuels—coal, petroleum, and natural gas. Fossil fuels formed over hundreds of millions of years, as dead organisms were covered with sediments and put under great pressure. Giant ferns in ancient swamps turned into coal deposits. The Figure below shows one way that coal deposits are mined. Dead organisms in ancient seas gradually formed deposits of petroleum and natural gas. 

Coal mines are a major source of hydrocarbons

Open-Pit Coal Mine

Summary

  • Hydrocarbons are compounds that contain only carbon and hydrogen. Hydrocarbons are the simplest type of carbon-based compounds.
  • Hydrocarbons vary greatly in size, which influences properties such as melting and boiling points. At room temperature, hydrocarbons may be gases, liquids, or solids. They are generally nonpolar and do not dissolve in water.
  • Hydrocarbons are placed in two basic classes—saturated and unsaturated hydrocarbons—based on the number of bonds between their carbon atoms.
  • Hydrocarbons have a wide variety of important uses, but their most important use is as fuels.
  • The main source of hydrocarbons is fossil fuels—coal, petroleum, and natural gas.

Review

  1. What is a hydrocarbon?
  2. Compare and contrast saturated and unsaturated hydrocarbons.
  3. List some uses of hydrocarbons.
  4. Where do hydrocarbons come from?

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Vocabulary

hydrocarbon

Carbon-based compound that contains only carbon and hydrogen.

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