Homologous Series
A homologous series is a family of organic compounds with the same functional group and the same general formula, where successive members differ by a CH2 group.
Practice This ConceptMain explanation
Teacher explanation
Members of a homologous series have similar chemical properties because they share the same functional group. Their physical properties show a gradual change as molecular mass increases. This idea helps students organise carbon compounds into families instead of learning them as isolated names.
Example
Methanol, ethanol, and propanol form a homologous series because each has the -OH group and each next member differs by CH2.
Simple analogy
Same group, same family, one CH2 more each step.
Common confusion
Students often think any group of carbon compounds is a homologous series. The same functional group and a fixed difference of CH2 are both required.
Exam tip
When comparing two compounds, check the functional group first and then see whether the formulas differ by CH2.
Answer writing and exam use
1-mark use
Write the exact meaning of homologous series in one clean line.
2-mark use
Define homologous series and add one example or condition.
3-mark use
Explain homologous series, show the method or example, and mention the common mistake.
Practice this concept with focused MCQs
Open the concept quiz intro first, review the test details, and then start a focused MCQ set from this concept only. Instant score and answer review are live now.
Help improve this page
Found something confusing, incorrect, or missing?