Homolog
Definition and meaning of Homolog in chemistry.
A homolog is a member of a specific family of organic chemical compounds. This family is called a homologous series and shares a general molecular formula. Each member in the group differs from the next by a constant repeating unit.
In more detail
Every homolog in a series contains the same functional group of atoms. This common group gives all members very similar chemical behaviors and reactions. The main difference between successive homologs is a single CH2 unit.
Adding this unit increases the molecular mass by fourteen atomic mass units. As the carbon chain grows longer, the physical properties of the compounds shift. For instance, the boiling point increases because the molecules have more surface area.
This extra surface area creates stronger attractive forces between the neighboring molecules. These attractive forces require more heat energy to break during boiling. Chemists can predict the traits of heavy homologs by studying the lighter ones.
Students sometimes confuse homologs with isomers, but their molecular formulas are different. Isomers have the exact same formula but different shapes, while homologs differ in size. This clear pattern helps us organize millions of unique organic molecules. It makes learning organic chemistry much simpler for students and researchers.
Key facts
| Field | Organic Chemistry |
|---|---|
| Constant Unit Difference | CH2 group |
| Mass Increase Per Step | Approximately 14 atomic mass units |
| Shared Feature | Same functional group |
| Physical Properties | Change gradually as chain length increases |
| Chemical Behavior | Highly similar across the series |
Methane, CH4, and ethane, C2H6, are two homologs in the alkane series. Both of these compounds are simple hydrocarbons that contain only single bonds. The formula for ethane has exactly one more carbon and two more hydrogens. This difference represents the standard CH2 group that defines the series. Propane, C3H8, is the next homolog because it adds another CH2 unit. All three gases burn easily in oxygen to produce carbon dioxide and water. Methane boils at a much lower temperature than ethane because it is smaller. This boiling point difference shows how the physical properties change down the series.
Frequently asked questions
Are homologs chemically identical?
No, homologs are not identical, but they have very similar chemical properties. Their reaction rates can change slightly as the molecules get larger and heavier.
How do homologs differ from isomers?
Homologs have different molecular formulas that change by a constant CH2 unit. Isomers share the exact same formula but have different shapes or connections.
Why do boiling points rise in a homologous series?
Larger homologs have more electrons and a greater surface area for contact. This creates stronger intermolecular forces that require more heat energy to break.