Chemistry (AS Level)·Hydrocarbons · NSSCAS 4.2.1
Alkanes
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Alkanes are the simplest organic family and the fuels we burn every day. Learn to read and use their general, structural, displayed and skeletal formulae, to name straight and branched alkanes up to six carbons, and to deduce a molecular formula from a drawing. Understand why alkanes are so unreactive, then work through their two real reactions — combustion, and free-radical substitution with chlorine or bromine — building the initiation, propagation and termination steps one at a time. Finally see how crude oil and cracking supply the hydrocarbons we use.
What you'll learn in this lesson
By the end you should be able to (NSSCAS Chemistry (AS Level) 4.2.1):
- Interpret and use the general (CₙH₂ₙ₊₂), structural, displayed and skeletal formulae of the alkanes
- Use systematic nomenclature to name alkanes up to six carbons, including branched examples such as 2,2-dimethylhexane
- Deduce the molecular formula of an alkane from its structural, displayed or skeletal formula
- Explain the general unreactivity of alkanes, including towards polar reagents (strong, non-polar C–C and C–H bonds)
- Describe the combustion of alkanes (complete and incomplete), using ethane
- Describe the substitution of ethane by chlorine and by bromine
- Describe the free-radical substitution mechanism: initiation (homolytic fission by UV), propagation and termination
- Explain the use of crude oil as a source of both aliphatic and aromatic hydrocarbons
- Explain that cracking breaks larger hydrocarbons into more useful smaller alkanes and alkenes of lower Mr
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