Alkanes
Chemistry: Edexcel IGCSE, topic 15.2.2
Alkanes
Hydrocarbons are organic compounds made of carbon and hydrogen. Hydrocarbons are the dominant compounds in crude oil. Most of these hydrocarbons are alkanes.
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Alkane structure
- In alkanes, carbon atoms bond to four atoms (hydrogen or carbon).
- We call them saturated hydrocarbons as all their bonds with other atoms are single bonds.
Alkane uses
- Alkanes have quite low reactivity, but they combust quite well.
- This makes them useful as fuels.
General formula
- Alkanes have the general formula CnH(2n+2)
- E.g. if a hydrocarbon contained 7 carbon atoms, the number of hydrogen atoms would be (2 x 7) + 2 = 16
- So, the formula for the hydrocarbon shown in the image would be C7H16
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Reaction with chlorine
- Although alkanes are quite unreactive, they will react with chlorine in the presence of UV light. The UV light activates the chlorine molecule, which starts the reaction.
- The overall reaction is a substitution reaction, as one hydrogen atom on the hydrocarbon is replaced by chlorine.
- The products formed are a chloroalkane and hydrogen chloride.
Test yourself on Alkanes
What is the molecular formula of an alkane with 10 carbon atoms?
If an alkane contains 21 carbon atoms, what will its formula be?
What two elements are hydrocarbons made from?
What products are formed when chlorine reacts with an alkane?