This lesson turns the alkane family into a usable naming and representation system. Students learn the Stage 5 IUPAC names for simple alkanes from `C1` to `C8`, recognise their formulas, and reproduce simple structures without drifting into senior-level organic chemistry.
Use the PDF for classwork, homework or revision. It includes key ideas, activities, questions, an extend task and success-criteria proof.
Write your best guess before reading. This lesson is about recognising and using the pattern, not just memorising a list.
Use the pattern from methane (1C), ethane (2C), propane (3C) and butane (4C) to predict the formulas.
Students should see alkane names as a logical sequence, not as eight unrelated words.
The Stage 5 sequence begins with `methane`, `ethane`, `propane` and `butane`, then continues through `pentane`, `hexane`, `heptane` and `octane`. Each name is linked to the number of carbon atoms in the chain. This is why naming matters: it gives students a reliable system for identifying and comparing simple hydrocarbons.
| Carbon number | Name | Molecular formula | Simple structural representation |
|---|---|---|---|
| 1 | Methane | CH4 | 1 carbon only |
| 2 | Ethane | C2H6 | CH3-CH3 |
| 3 | Propane | C3H8 | CH3-CH2-CH3 |
| 4 | Butane | C4H10 | four-carbon chain |
| 5 | Pentane | C5H12 | five-carbon chain |
| 6 | Hexane | C6H14 | six-carbon chain |
| 7 | Heptane | C7H16 | seven-carbon chain |
| 8 | Octane | C8H18 | eight-carbon chain |
Students do not need advanced structure drawing conventions here. What matters is being able to represent simple straight-chain alkanes clearly and connect name, carbon number and formula.
When students represent simple alkanes, they should focus on the carbon chain and the idea that hydrogen atoms complete the structure. A simple Stage 5 representation might show a straight chain of carbon atoms with enough hydrogens attached to satisfy the formula. This is enough for naming and recognition at this level.
This lesson is not just a naming exercise. Students need these names and formulas so they can talk clearly about hydrocarbon fuels, crude oil fractions and later polymer-related ideas. If the naming pattern is secure, later lessons become easier to interpret and compare.
Wrong: The formula of an alkane tells you how many molecules are joined together.
Right: The molecular formula shows the number of each type of atom in one molecule, not how many molecules are joined.
Wrong: Alkane names are random words with no pattern.
Right: Alkane names follow a systematic pattern linked to the number of carbon atoms: meth- (1), eth- (2), prop- (3), but- (4), pent- (5), hex- (6), hept- (7), oct- (8).
Right: Simple structural representations help connect name to formula and are a useful Stage 5 skill for understanding carbon chains.
Right: C2H6 has two carbon atoms and six hydrogen atoms. The subscript after each symbol tells you how many of that element are in the molecule.
Select the correct IUPAC name for each alkane formula.
CH₄
C₃H₈
C₄H₁₀
Simple alkanes are named in a carbon-number sequence: methane, ethane, propane, butane, pentane, hexane, heptane and octane.
Students should recognise the names, formulas and simple straight-chain representations of alkanes from `C1` to `C8`.
Simple structures help connect the name of an alkane to its carbon chain and molecular formula.
This naming system supports later lessons on combustion, crude-oil products and polymers.
Match each formula to its alkane name: `CH4`, `C3H8`, `C5H12`, `C8H18`.
Explain how the alkane name tells you something about the structure.
Claim: State what the alkane name tells you about the structure.
Evidence: Use examples from the lesson such as methane, propane or octane.
Reasoning: Explain how the carbon-number prefix system creates a predictable pattern.
1. Which is the correct IUPAC name for `C2H6`?
2. Which formula matches `octane`?
3. Which alkane has five carbon atoms?
4. Why are simple structural representations useful in this unit?
5. Which statement best matches the correct Stage 5 scope?
Name the alkane with formula `C4H10` and explain what the name tells you. 1 mark for identifying butane. 1 mark for stating that "but-" means four carbons. 1 mark for linking the name to the formula C4H10.
How would you distinguish `hexane` from `heptane` using name, formula and carbon number. 1 mark for stating hexane has six carbons and formula C6H14. 1 mark for stating heptane has seven carbons and formula C7H16. 1 mark for explaining the name difference (hex- vs hept-). 1 mark for linking the formula difference to carbon number.
Why is it better to learn the alkane naming system as a pattern rather than as unrelated words? 1 mark for stating the naming system follows a pattern. 1 mark for giving an example of the pattern. 1 mark for explaining that patterns are easier to remember. 1 mark for linking this to later topics such as fuels or combustion.
Return to the opening question. Can you now explain what naming pattern the simple alkane family follows?
1: C. `C2H6` is ethane.
2: A. `octane` has formula `C8H18`.
3: D. `pentane` has five carbon atoms.
4: B. Simple structures help connect names, formulas and carbon chains.
5: A. That statement matches the correct Stage 5 scope.
Sample answer: The alkane with formula `C4H10` is butane. The name tells me that the molecule has a four-carbon chain because the prefix `but-` is linked to four carbons in the alkane sequence.
1 mark for identifying butane. 1 mark for stating that "but-" means four carbons. 1 mark for linking the name to the formula C4H10.
Sample answer: Hexane has six carbon atoms and formula `C6H14`. Heptane has seven carbon atoms and formula `C7H16`. They differ because the name, carbon number and formula all shift together in the alkane pattern.
1 mark for stating hexane has six carbons and formula C6H14. 1 mark for stating heptane has seven carbons and formula C7H16. 1 mark for explaining the name difference (hex- vs hept-). 1 mark for linking the formula difference to carbon number.
Sample answer: It is better because a pattern is easier to remember and use than unrelated words. The pattern helps with naming, matching formulas and understanding carbon-chain length. This matters later because students need to talk clearly about fuels, crude-oil products and organic materials.
1 mark for stating the naming system follows a pattern. 1 mark for giving an example of the pattern. 1 mark for explaining that patterns are easier to remember. 1 mark for linking this to later topics such as fuels or combustion.
Simple alkanes follow an IUPAC naming pattern from methane through octane.
Students should recognise the names and formulas of simple alkanes from `C1` to `C8`.
Simple structural representations help connect carbon number, formula and name.
Next lesson applies hydrocarbon knowledge to combustion.