AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
Crude oil, hydrocarbons and alkanes: The first four members of the alkanes are methane, ethane, propane and butane.
The alkane homologous series begins with the simplest member, methane, which has one carbon atom and the formula CH₄.
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
The alkane homologous series begins with the simplest member, methane, which has one carbon atom and the formula CH₄. The next three members are ethane (two carbon atoms, C₂H₆), propane (three carbon atoms, C₃H₈) and butane (four carbon atoms, C₄H₁₀). Their names use stems that indicate the number of carbon atoms: meth- for one, eth- for two, prop- for three and but- for four, with the ending -ane showing membership of the alkane family. Each successive member has one more carbon atom and two more hydrogen atoms than the previous one, so the formulas follow CₙH₂ₙ₊₂. These four are important fuels: methane is natural gas, propane and butane are used in bottled gas, and all burn in plentiful oxygen to produce carbon dioxide and water.
What earns the marks
- The first four alkanes are methane, ethane, propane and butane, in order of increasing carbon chain length.
- Their molecular formulas are CH₄, C₂H₆, C₃H₈ and C₄H₁₀ respectively.
- The prefixes meth-, eth-, prop- and but- indicate one, two, three and four carbon atoms.
- Each successive alkane has one more carbon atom and two more hydrogen atoms than the previous member.
Common mistakes and how to put them right
Mixing up the order or formulas, such as giving propane as C₃H₆.
Put it right: Propane is C₃H₈ because it is an alkane.
Using the wrong prefix, for example writing 'methene' or 'buthene' for an alkane.
Put it right: The -ane ending is essential.
Assuming methane contains more than one carbon atom because it is a common fuel.
Put it right: Methane is CH₄ with a single carbon atom.
Exam tips
- Learn the first four names and formulas as a sequence so you can recall them quickly.
- Use the prefix to count carbon atoms and the general formula to check the hydrogen count.
- When naming an alkane from a displayed formula, count the carbon atoms first, then choose the correct prefix and add -ane.
Try the lesson
The start of the Crude oil, hydrocarbons and alkanes: The first four members of the alkanes are methane, ethane, propane and butane. lesson, made from checked teaching notes for this specification point.
Have a go first
Which of these is the name of the first member of the alkanes?
Listen
The alkane homologous series begins with the simplest member, methane, which has one carbon atom and the formula CH₄. The next three members are ethane (two carbon atoms, C₂H₆), propane (three carbon atoms, C₃H₈) and butane (four carbon atoms, C₄H₁₀). Their names use stems that indicate the number of carbon atoms: meth- for one, eth- for two, prop- for three and but- for four, with the ending -ane showing membership of the alkane family. Each successive member has one more carbon atom and two more hydrogen atoms than the previous one, so the formulas follow CₙH₂ₙ₊₂. These four are important fuels: methane is natural gas, propane and butane are used in bottled gas, and all burn in plentiful oxygen to produce carbon dioxide and water. A strong answer earns marks for these points. The first four alkanes are methane, ethane, propane and butane, in order of increasing carbon chain length. Their molecular formulas are CH₄, C₂H₆, C₃H₈ and C₄H₁₀ respectively. The prefixes meth-, eth-, prop- and but- indicate one, two, three and four carbon atoms. Each successive alkane has one more carbon atom and two more hydrogen atoms than the previous member. Exam tip: Learn the first four names and formulas as a sequence so you can recall them quickly.
See it
Put it in order
Put these steps in the order they happen.
- 1. ethane
C₂H₆
2 carbon atoms - 2. propane
C₃H₈
3 carbon atoms - 3. butane
C₄H₁₀
4 carbon atoms - 4. methane
CH₄
1 carbon atom
Key words
Say what each word means before you turn the card.
meth-
Try answering aloud or in your head before turning the card.
eth-
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prop-
Try answering aloud or in your head before turning the card.
but-
Try answering aloud or in your head before turning the card.
See every definition
- meth-
- Prefix used in the names of alkanes to indicate one carbon atom.
- eth-
- Prefix used in the names of alkanes to indicate two carbon atoms.
- prop-
- Prefix used in the names of alkanes to indicate three carbon atoms.
- but-
- Prefix used in the names of alkanes to indicate four carbon atoms.
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
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