Physical Properties of Alkanes
Learn about the trends in boiling points, melting points, density, and solubility of alkanes based on molecular size and branching.
What is Physical Properties of Alkanes?
Weak, short-range electrostatic attractive forces between uncharged molecules, arising from the temporary changes in the electron distribution within the molecules.
Key points
- Explain the trend in boiling points and melting points of alkanes.
- Describe the effect of branching on the boiling points of alkanes.
- Relate the density of alkanes to their molecular structure.
- Predict the solubility of alkanes in different solvents.
Common exam trap
Assuming boiling point increases indefinitely with branching.
Definitions
- Term
Van der Waals forces
- Meaning
Weak, short-range electrostatic attractive forces between uncharged molecules, arising from the temporary changes in the electron distribution within the molecules.
- Term
London Dispersion Forces
- Meaning
A type of van der Waals force that arises from temporary, instantaneous dipoles in molecules, which induce dipoles in neighboring molecules, leading to a weak attraction.
- Term
Homologous Series
- Meaning
A series of organic compounds with the same functional group and general formula, in which successive members differ by CH2 group.
- Term
Isomers
- Meaning
Molecules with the same molecular formula but different structural formulas, leading to different physical and chemical properties.
Learning objectives
Explain the trend in boiling points and melting points of alkanes.
Describe the effect of branching on the boiling points of alkanes.
Relate the density of alkanes to their molecular structure.
Predict the solubility of alkanes in different solvents.
Prerequisites
Structure of Alkanes (Homologous Series)
Intermolecular Forces (Van der Waals forces, London Dispersion Forces)
Molecular Weight and its relation to size
Common mistakes
Assuming boiling point increases indefinitely with branching.
Confusing solubility trends (polar vs. nonpolar).
Overlooking the effect of molecular weight on density.
Incorrectly predicting the state (gas, liquid, solid) based on carbon number.
Keywords
Alkanes
Physical Properties
Boiling Point
Melting Point
Density
Solubility
Van der Waals Forces
London Dispersion Forces
Branching
Isomers
Homologous Series
Nonpolar
Practice preview
Which of the following alkanes has the highest boiling point?…
easy
The density of alkanes generally:…
easy
Alkanes are generally:…
easy