Homologous Series (Cambridge O Level Chemistry)

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Last updated

2 November 2023

This is a series or family of organic compounds that have similar features and chemical properties due to them having the same functional group
The functional group is a group of atoms which are bonded in a specific arrangement that is responsible for the characteristic reactions of each member of a homologous series

homologous-series-table

Make sure you can identify the functional group for each homologous series.

This type of formula tells you the composition of any member of a whole homologous series of organic compound
For example, all of the alkanes have the general formula C_nH_2n+2, where n represents the number of carbon atoms
This tells you that however many carbon atoms there are in the alkane, doubling this number and adding two will give you the number of hydrogen atoms present in the alkane
General formulae can be used to work out the formula of a compound from different homologous series if the number of carbon atoms present is known

What is the formula of an alcohol that contains 5 carbon atoms?

Answer

A compound has the formula C₁₂H₂₄. To which homologous series does this compound belong to?

Answer

There are 12 carbon atoms, so n = 12
There are twice the number of hydrogen atoms than carbon atoms = 2n
Therefore the general formula of the compound is C_nH_2n which means this compound is an alkene