London Dispersion Forces

Definition

London dispersion forces are weak, temporary attractive forces that occur between all atoms and molecules due to the momentary distribution of electrons. These forces arise from the formation of instantaneous dipoles that can induce dipoles in neighboring particles, leading to an attraction. They are essential for understanding various physical properties and behaviors of substances, especially in relation to intermolecular forces and crystal structures.

5 Must Know Facts For Your Next Test

1. London dispersion forces are present in all molecules, regardless of their polarity, making them a universal force.
2. These forces increase with the size of the molecules and their surface area; larger molecules have more electrons and can create stronger temporary dipoles.
3. In nonpolar substances, London dispersion forces are often the only type of intermolecular force present.
4. London dispersion forces are weaker than hydrogen bonds and dipole-dipole interactions but play a significant role in the physical properties of noble gases and hydrocarbons.
5. When considering crystal structures, London dispersion forces can influence packing efficiency and overall stability of the structure.

Review Questions

• How do London dispersion forces compare to other types of intermolecular forces in terms of strength and significance?
  • London dispersion forces are generally the weakest type of intermolecular force compared to dipole-dipole interactions and hydrogen bonding. While they may not be as strong, they are critical in understanding how nonpolar substances behave and interact with each other. Additionally, their strength increases with molecular size, affecting physical properties like boiling and melting points.
• Discuss how London dispersion forces contribute to the properties of nonpolar substances.
  • In nonpolar substances, London dispersion forces are the primary form of intermolecular attraction. They allow these molecules to exhibit cohesive properties, contributing to characteristics like boiling points and solubility in various solvents. For example, larger nonpolar hydrocarbons experience stronger London dispersion forces due to increased electron cloud size, resulting in higher boiling points compared to smaller nonpolar molecules.
• Evaluate the role of London dispersion forces in determining the crystal structure stability of certain materials.
  • London dispersion forces play a crucial role in stabilizing crystal structures, particularly for substances composed of nonpolar molecules or atoms, such as noble gases or hydrocarbons. The cumulative effect of these weak forces can lead to significant stabilization within a crystal lattice. As molecular size increases, the strength of London dispersion forces also increases, affecting how tightly molecules pack together and ultimately influencing the overall stability and physical properties of the material.

Related terms

Dipole-Dipole Interactions:

Attractive forces between polar molecules that occur when the positive end of one molecule is attracted to the negative end of another.

Hydrogen Bonding: A specific type of strong dipole-dipole interaction that occurs when hydrogen is bonded to highly electronegative elements like nitrogen, oxygen, or fluorine.

Intermolecular Forces: Forces that act between molecules, influencing physical properties like boiling point, melting point, and solubility.