Alkanes and alkenes

Part of Edexcel C2 topic Synthesis. Basic info about alkanes and alkenes.

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Hydrocarbon = an organic compound containing only hydrogen and carbon

When there is more than one carbon atom, they are joined by single covalent bonds


Each carbon atom has formed the maximum number of bonds - it is saturated

This is known as an alkane

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Types of alkane

The simplest alkane is methane which is made up of 1 carbon atom and 4 hydrogen atoms. Its formula is CH4


The next 3 alkanes are:

Ethane - C2H6

Propane - C3H8

Butane - C4H10

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Alkenes are similar to alkanes but differ in the fact that two of the carbon atoms are joined by a double covalent bond


The carbon atoms have not formed the maximum number of bonds (as the double bond can open up to join to more atoms) - they are unsaturated


To work out if a hydrocarbon is an alkane or an alkene, add bromine water. Alkenes will make the bromine water go colourless, but alkanes have no effect and the bromine water will stay brown/orange

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Types of alkene

The simplest alkene is ethene which is made up of 2 carbon atoms and 4 hydrogen atoms. Its formula is C2H4


The next 2 alkenes are:

Propene - C3H6

Butene - C4H8


There is no alkene with only one carbon atom as an alkene always has a double bond between 2 carbon atoms

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Alkane and alkene names

You can work out the number of carbon atoms in an alkane or alkene by looking at the beginning of its name

Meth = 1

Eth = 2

Prop = 3

But = 4                             etc.

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Alkane and alkene formulas

You can use these simple formulas to work out the formula of an alkane or alkene:

Alkane - There is twice the number of hydrogen atoms as carbon atoms plus two more. E.g. if there are 4 carbon atoms there are 10 hydrogen atoms.

Use: CnH2n+2                     (where n = any number)


Alkene - There are twice the number of hydrogen atoms as carbon atoms

Use: CnH2n                         (where n = any number)

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