What is a homologous series? Give its features, and write the names and formulas of the first three members of the alcohol series.

1. 1 · Define in one line. A homologous series is a series of carbon compounds with the same functional group, in which each member differs from the next by -CH₂-.
2. 2 · Give the features.
   • The same general formula and similar chemical properties.
   • The molecular mass rises by 14 u at each step.
   • Physical properties, such as melting and boiling points, change gradually.
3. 3 · Write the example. Methanol CH₃OH, ethanol C₂H₅OH, propanol C₃H₇OH: each has the -OH group, and each differs from the next by -CH₂-.
4. 4 · Link to real life. Ethanol, the second member, is used in hand sanitisers and medicines.
5. 5 · Close in one line. So knowing one member helps you predict the chemistry of the whole series.

Scoring tip: Write the three formulas one below the other, so the -CH₂- difference is easy to see.