Fun Fact: Ever wondered how petroleum refineries separate various hydrocarbons? They use a technique called fractional distillation, and it’s all about boiling points!

A homologous series is a group of organic compounds that share a common functional group. Each member of a homologous series differs from the next by an increment of CH2 (a carbon atom and two hydrogen atoms).

The functional group in an organic compound determines the type of characteristic reactions the compound can undergo. All members of a homologous series have similar chemical properties due to their shared functional group.

• Boiling Points: Boiling points of straight-chain alkanes in a homologous series increase as the number of carbon atoms in the chain increases. The correlation between carbon chain length and boiling point is quite consistent.
  • Reason: As the carbon chain length increases, the London (dispersion) forces between molecules become stronger, leading to higher boiling points.
  • Real-world example: Let's consider crude oil, which is a mixture of hydrocarbons with varying carbon chain lengths. In the petrochemical industry, fractional distillation is used to separate these hydrocarbons based on their boiling points. The oil is vaporized, and as the vapor rises through a column, it cools, and compounds with different boiling points condense at different levels.
• Melting Points: Melting points also increase with increasing molar mass, but the trend is not as smooth as boiling points. Therefore, predicting melting points is less certain.
• Density and Viscosity: Both density and viscosity of members of a homologous series increase with carbon chain length.