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GCSE Chemistry Revision
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GCSE Chemistry revision
Crude oil, hydrocarbons and alkanes
Carbon compounds as fuels and feedstock
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AQA student objectives
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All · Most · Some
Revision summary
Key knowledge
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Introduction
- Organic chemistry is the branch of chemistry that studies compounds containing carbon.
- Carbon is particularly useful in forming large compounds because each carbon atom can form four strong covalent bonds.
- The most common bonding partners for carbon atoms are other carbon atoms and hydrogen atoms.
Defining Hydrocarbons
- A hydrocarbon is any compound formed from carbon and hydrogen only.
- Butane is an example of a hydrocarbon, whereas butanol is not, because it also contains an oxygen atom.
The First Four Alkanes
- Alkanes are the simplest group of hydrocarbons, and you need to know the first four members of the series.
- Methane (CH₄) contains one carbon atom bonded to four hydrogen atoms.
- Ethane has the molecular formula C₂H₆, propane is C₃H₈, and butane is C₄H₁₀.
- Each successive alkane in the series increases by one carbon atom and two hydrogen atoms.
Homologous Series & General Formula
- Alkanes belong to a homologous series, meaning they share similar chemical properties and react in similar ways.
- The general formula for alkanes is CₙH₂n₊₂, where n represents the number of carbon atoms.
- For example, octane has 8 carbon atoms, so it has 2 × 8 + 2 = 18 hydrogen atoms, giving the molecular formula C₈H₁₈.
Saturated Compounds
- A key feature of alkanes is that they are saturated compounds, meaning every carbon atom forms four single covalent bonds with no double bonds present.
- If a single bond in an alkane were changed to a double bond, the compound would no longer be an alkane but would instead become an alkene.