Crude Oil, Hydrocarbons and Fractional Distillation
Hydrocarbons: Structure and Naming
This GCSE chemistry lesson explores Crude Oil, Hydrocarbons and Fractional Distillation. Students describe crude oil as a mixture of hydrocarbons, explain fractional distillation and compare the properties, uses and reactions of alkanes and alkenes. It supports KS4 classroom teaching, independent study and exam revision using clear, subject-specific vocabulary.
Lesson duration is: 55 minItems in this lesson
Hydrocarbons: Structure and Naming
This GCSE chemistry lesson explores Crude Oil, Hydrocarbons and Fractional Distillation. Students describe crude oil as a mixture of hydrocarbons, explain fractional distillation and compare the properties, uses and reactions of alkanes and alkenes. It supports KS4 classroom teaching, independent study and exam revision using clear, subject-specific vocabulary.
Hydrocarbons, KS4 Chemistry, GCSE Chemistry, Crude Oil, Alkanes, Alkenes, Fractional Distillation, Saturated Hydrocarbons, Unsaturated Hydrocarbons, Combustion, Complete Combustion, Incomplete Combustion, Cracking, General Formula, Structural Formula, Displayed Formula, Homologous Series, Addition Reactions, Bromine Water Test, MCQs, Open Questions, Polls, Emoji Polls, Exit Tickets
Learning goal
I can describe the structure, naming and main properties of hydrocarbons, and distinguish between alkanes, alkenes and simple aromatic hydrocarbons.
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Try and name everything you can think of that relates to hydrocarbons
Use this to surface prior ideas such as fuels, oil, carbon, hydrogen, petrol, gas, pollution or burning. Briefly sort responses into accurate science terms and everyday associations.
What are hydrocarbons?
Compounds made only of carbon and hydrogen
Found in fuels, crude oil and many organic substances
Different hydrocarbons have different numbers and arrangements of atoms
Keep the definition precise: no oxygen, nitrogen or other elements. Link to prior knowledge of atoms, covalent bonding and fuels.
Why hydrocarbons matter
Many hydrocarbons burn and release useful energy
They are the main chemical family in crude oil
Crude oil is separated into fractions, each containing hydrocarbons with similar boiling points
Hydrocarbons are also used as starting materials for making other chemicals
Do not drift too far into fractional distillation detail; the point here is that hydrocarbons are chemically and economically important, especially as fuels and feedstocks.
Families of hydrocarbons
Alkanes: saturated hydrocarbons
Alkenes: unsaturated hydrocarbons
Simple aromatic hydrocarbons: ring structures such as benzene
These families differ in bonding, formula patterns and reactivity
This slide sets up the lesson classification. Keep aromatic hydrocarbons at a simple recognition level rather than detailed mechanism.
Saturated and unsaturated
A saturated hydrocarbon has only single carbon-carbon bonds. An unsaturated hydrocarbon has at least one carbon-carbon double bond. This difference in bonding changes how the molecules react.
Students often think saturated means 'full of hydrogen' in a vague sense; make clear that it specifically refers to having no C=C double bonds in this context.
Alkanes: structure
Contain only single covalent bonds
Each carbon forms four bonds overall
Straight-chain alkanes follow the general formula CₙH₂ₙ₊₂
Examples: methane CH₄, ethane C₂H₆, propane C₃H₈
If useful, sketch displayed or structural formulae to show how carbon makes four bonds and hydrogen makes one.
Alkanes: properties
Usually quite unreactive compared with alkenes
Non-polar, so they do not mix with water
Often used as fuels because they burn in oxygen
Link low reactivity to the absence of a C=C double bond. Avoid overcomplicating with full combustion equations unless needed by the class.
Which statement correctly describes an alkane?
Only single bonds
Contains a ring
Has a double bond
Mixes with water
Checks the first classification block: hydrocarbons, families, saturation and alkane structure/properties. Distractors match nearby misconceptions: confusing aromatics with alkanes, mixing up alkenes, and assuming fuels dissolve in water.
Complete the summary
A hydrocarbon contains only carbon and hydrogen. In an alkane, the carbon atoms are joined by single bonds, so it is described as saturated. Straight-chain alkanes follow the general formula CₙH₂ₙ₊₂.
All blanks are load-bearing terms from slides 2 to 7.
Alkenes: structure
Contain at least one carbon-carbon double bond
Straight-chain alkenes with one double bond follow CₙH₂ₙ
Examples: ethene C₂H₄, propene C₃H₆, butene C₄H₈
The double bond makes them unsaturated
Emphasise that the general formula given here is for simple acyclic alkenes with one double bond.
Why alkenes are more reactive
The carbon-carbon double bond in an alkene is the key reactive part of the molecule. Because of this bond, alkenes react more easily than alkanes in addition reactions, where atoms are added across the double bond.
Keep the explanation accessible: students need the link between bonding and reactivity, not orbital detail.
Bromine water test
Alkenes react with bromine water
The orange colour is decolourised
This is a test for unsaturation
Alkanes do not decolourise bromine water in these conditions
Name the reaction as addition. If appropriate, use ethene + bromine as the example but keep the main focus on the observation and what it means.
Simple aromatic hydrocarbons
Aromatic hydrocarbons contain a ring structure
The simplest example is benzene, C₆H₆
Benzene is not an alkane or an alkene
Aromatic hydrocarbons form their own important family
Students only need to recognise simple aromatic hydrocarbons here. Avoid advanced bonding models unless the specification requires more depth.
What does bromine water show about a hydrocarbon?
It is aromatic
It is saturated
It is unsaturated
It is non-polar
Links the bromine water observation to unsaturation, not just to 'being an alkene' by name.
Complete the explanation
Alkenes contain a carbon-carbon double bond. This makes them unsaturated and usually more reactive than alkanes. In bromine water, the orange colour is decolourised because an addition reaction happens across the double bond.
Use the completed paragraph to restate the bonding-reactivity link in simple terms.
Why is benzene not an alkene?
Expected answer elements: aromatic hydrocarbons have a ring structure; benzene is the simplest example; they are a separate family, not alkanes or alkenes.
Naming straight-chain hydrocarbons
The prefix shows the number of carbons: meth-, eth-, prop-, but-, pent-
The ending shows the family: -ane for alkanes, -ene for alkenes
Examples: propane, butane, ethene, pentene
Focus on basic IUPAC naming for straight chains only. You can mention that the double bond position matters in larger molecules, but do not build that as the main content unless needed.
From formula to name
C₁H₄ → methane
C₂H₆ → ethane
C₃H₈ → propane
C₂H₄ → ethene
C₄H₈ → butene
Point out how the formula pattern helps students decide whether a simple hydrocarbon is likely to be an alkane or alkene.
Isomerism in simple hydrocarbons
Some hydrocarbons have the same molecular formula but different structural arrangements. These are isomers. For example, C₄H₁₀ can be arranged as a straight chain or a branched chain.
A quick sketch of butane and methylpropane will help. Keep the idea at simple structural isomerism rather than adding positional or geometric isomerism.
Comparing the three families
Alkanes: single bonds, saturated, less reactive
Alkenes: at least one double bond, unsaturated, more reactive
Aromatic hydrocarbons: ring-based structures such as benzene
Use this as the landing comparison that answers the lesson question: students should now be able to sort examples into the correct family and justify why.
Which name matches the formula C4H8?
butane
butene
propene
pentene
Requires students to use both the prefix for carbon number and the alkene formula pattern.
Complete the naming summary
In straight-chain hydrocarbon names, the prefix shows the number of carbons. The ending -ane means alkane and -ene means alkene. Compounds with the same molecular formula but different structures are called isomers.
Echoes slides 12 to 15 and reinforces naming plus simple structural isomerism.
How well do you feel you feel you understand crude oil and hydrocarbons now?
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Glossary
hydrocarbon - a compound made only of carbon and hydrogen
saturated - having only single carbon-carbon bonds
unsaturated - having at least one carbon-carbon double bond
alkane - a saturated hydrocarbon with only single bonds
alkene - an unsaturated hydrocarbon with at least one double bond
aromatic hydrocarbon - a hydrocarbon with a ring structure such as benzene
general formula - a formula that shows the pattern for a whole family of compounds
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Glossary
IUPAC naming - a standard system for naming chemical compounds
isomer - one of two or more compounds with the same molecular formula but different structures
addition reaction - a reaction where atoms are added across a double bond
bromine water - an orange solution used to test for unsaturation
benzene - a simple aromatic hydrocarbon with the formula C₆H₆
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