London Dispersion Forces

Definition

London dispersion forces are weak intermolecular forces that arise from temporary dipoles created when electrons in a molecule are distributed unevenly. These forces are present in all molecules, whether polar or nonpolar, and play a crucial role in determining the physical properties of substances, especially those with larger atoms or molecules where these fluctuations in electron density are more pronounced.

5 Must Know Facts For Your Next Test

1. London dispersion forces increase with larger molecular size and greater surface area, leading to stronger attractions between larger molecules.
2. These forces are the weakest type of intermolecular force but are significant in nonpolar substances like noble gases and hydrocarbons.
3. Even though they are weak, London dispersion forces can accumulate and become substantial enough to affect the boiling points of nonpolar compounds.
4. London dispersion forces are a result of instantaneous dipoles that form due to fluctuations in electron distribution around a nucleus.
5. All molecules, including nonpolar ones, exhibit London dispersion forces, which makes them essential for understanding molecular interactions.

Review Questions

• How do London dispersion forces compare to other types of intermolecular forces in terms of strength and importance?
  • London dispersion forces are the weakest intermolecular forces compared to dipole-dipole interactions and hydrogen bonds. While they may be minor individually, their cumulative effect can significantly influence the physical properties of larger molecules. Understanding these forces is essential for explaining why nonpolar substances can still exhibit unique behaviors despite lacking stronger intermolecular attractions.
• Discuss how molecular size affects the strength of London dispersion forces and provide examples.
  • The strength of London dispersion forces increases with molecular size because larger molecules have more electrons and a greater surface area, allowing for more significant fluctuations in electron density. For example, larger hydrocarbons like octane exhibit stronger London dispersion forces compared to smaller hydrocarbons like methane. This results in higher boiling points for larger molecules due to the increased attraction between them.
• Evaluate the role of London dispersion forces in the physical properties of nonpolar substances and their significance in various applications.
  • London dispersion forces play a critical role in determining the physical properties of nonpolar substances, such as boiling points and solubility. In many applications, like cryogenics or material science, understanding these forces helps predict how nonpolar gases behave at different temperatures and pressures. This evaluation is essential for designing systems that involve nonpolar materials, ensuring efficiency and safety in their usage across various fields.

Related terms

Intermolecular Forces:

Forces that occur between molecules, influencing their physical properties and behavior, including boiling points and melting points.

Polar Molecules: Molecules that have a net dipole moment due to the presence of polar bonds, resulting in an uneven distribution of electron density.

Dipole-Dipole Interactions: Attractive forces between the positive end of one polar molecule and the negative end of another, which are generally stronger than London dispersion forces.