Higher and foundation tier

Organic chemistry is probably one of the largest area of study in chemistry. It is concerned with compounds that contain the element carbon. Hydrocarbons are organic compounds molecules made up of the elements hydrogen and carbon only. Hydrocarbons are found in crude oil. Crude oil is a thick, tacky "liquid" made of many thousands of organic compounds all mixed together. Crude oil is often described as the "life blood of industrial nations" because of the many valuable substances it contains. Crude oil is extracted from under the oceans and on land in many countries spread over the globe including: Venezuela, Saudi Arabia, Iran, Iraq, UAE Russia, China, Brazil, Canada as well as many others.

Most of the compounds in crude oil are hydrocarbons. There are thousands of hydrocarbons and to make it easy to name and identify them all they are placed in groups or families. The simplest family is called the alkanes. The alkanes are hydrocarbons which have single covalent bonds between the carbon and hydrogen atoms. The first 4 members of the alkanes are methane, ethane, propane and butane. They are shown in the image below.

3d models of alkanes

The alkanes shown in the image all have a backbone of carbon atoms which is surrounded by a sea of hydrogen atoms. Each atom of carbon as you would expect makes 4 covalent bonds and each atom of hydrogen makes 1 covalent bond. The alkanes are described as saturated since they have a single covalent bonds between the atoms of carbon. The alkanes molecules are shown in 3-d in the image above but often they are drawn out as flat molecules, generally we are not overly concerned with the shapes of the molecules. The first 5 alkanes are shown below as flat molecules.

The first 6 alkanes

If you study the formula for each of the alkanes you will notice that in going from one alkane to the next we simply add -CH2 each time.

the formula for the first 4 alkanes

The alkanes form a homologous series, that is a series of compounds which all have the same general formula and show trends or patterns in their chemical and physical properties. You can work out the formula for any alkane using the general formula CnH2n+2, so for example decane has 10 carbon atoms, what is its formula? If you substitute 10 into the general formula , then to get number of hydrogens, (2x10)+2=22. So the formula for decane is C10H22.

Key Points

Practice questions

Check your understanding - Questions on the alkanes