2. Physical trends in homologous series

Homologous Series

A series of organic compounds with the same functional group and similar chemical properties but different physical properties.

Why do members of the same homologous series have similar chemical properties?

Because they have the same functional group, which determines the types of characteristic reactions they undergo.

How do physical properties change in a homologous series?

Physical properties such as melting and boiling points change gradually as the carbon chain increases by CH₂, altering intermolecular forces.

Why does the boiling point increase with increasing molar mass in a homologous series?

Due to stronger London (dispersion) forces as the carbon chain length increases.

Why is the trend in melting points less predictable than boiling points in a homologous series?

Because melting points are affected by factors such as molecular symmetry and packing in the solid state, making the trend less smooth.

How can boiling points of successive members of a homologous series be measured?

Using a simple distillation apparatus and a temperature probe.

What type of intermolecular force is responsible for the trend in boiling points?

London (dispersion) forces, which exist between all molecules and become stronger as the molecule's size increases.

How does fractional distillation separate hydrocarbons in crude oil?

Hydrocarbons condense at different temperatures based on their boiling points. Long-chain hydrocarbons condense lower in the column, while short-chain hydrocarbons condense higher where it is cooler.

Fractional Distillation

A process that separates components in a mixture based on differences in their boiling points.

Crude Oil Refining

The separation of hydrocarbons in crude oil using fractional distillation, where long-chain hydrocarbons condense at the bottom and short-chain hydrocarbons condense at the top of the column.

London (Dispersion) Forces

Weak intermolecular forces present in all molecules, increasing in strength with larger molecular size.