Dispersion Forces

Definition

Dispersion forces, also known as London dispersion forces, are a type of intermolecular force that arises from the temporary, fluctuating dipoles that can form in all atoms and molecules. These forces play a crucial role in the structure and general properties of nonmetals.

5 Must Know Facts For Your Next Test

1. Dispersion forces are present in all atoms and molecules, even those without permanent dipole moments, such as noble gases and nonpolar molecules.
2. The strength of dispersion forces increases with the size and polarizability of the atoms or molecules involved, as larger and more polarizable species can form stronger temporary dipoles.
3. Dispersion forces are responsible for the condensation of nonpolar gases, such as the liquefaction of oxygen and nitrogen, and the relatively high boiling points of nonpolar substances, such as methane and carbon dioxide.
4. Dispersion forces are the dominant intermolecular force in nonpolar substances and play a significant role in the physical properties of nonmetals, such as their melting and boiling points, surface tension, and viscosity.
5. The ability of dispersion forces to hold molecules together is the reason why nonpolar substances, such as waxes and oils, can form thin, cohesive films on surfaces.

Review Questions

• Explain how dispersion forces arise and their relationship to the structure and properties of nonmetals.
  • Dispersion forces arise from the temporary, fluctuating dipoles that can form in all atoms and molecules, even those without permanent dipole moments, such as noble gases and nonpolar molecules. The strength of these forces increases with the size and polarizability of the atoms or molecules involved, as larger and more polarizable species can form stronger temporary dipoles. Dispersion forces are the dominant intermolecular force in nonpolar substances and play a significant role in the physical properties of nonmetals, such as their melting and boiling points, surface tension, and viscosity. For example, the ability of dispersion forces to hold molecules together is the reason why nonpolar substances, such as waxes and oils, can form thin, cohesive films on surfaces.
• Describe the relationship between polarizability and the strength of dispersion forces, and explain how this affects the properties of nonmetals.
  • The strength of dispersion forces is directly related to the polarizability of the atoms or molecules involved. Larger and more polarizable species, such as heavier atoms or larger molecules, can form stronger temporary dipoles, resulting in stronger dispersion forces. This relationship between polarizability and dispersion force strength is crucial in understanding the physical properties of nonmetals. For instance, the relatively high boiling points of nonpolar substances, such as methane and carbon dioxide, are due to the strong dispersion forces that hold these molecules together. Similarly, the condensation of nonpolar gases, such as the liquefaction of oxygen and nitrogen, is driven by the attractive dispersion forces between the molecules. The ability of dispersion forces to influence these macroscopic properties of nonmetals is a direct consequence of their dependence on the polarizability of the constituent atoms and molecules.
• Evaluate the role of dispersion forces in the structure and general properties of nonmetals, and explain how this knowledge can be applied to predict and understand the behavior of these substances.
  • Dispersion forces play a fundamental role in the structure and general properties of nonmetals. As the dominant intermolecular force in nonpolar substances, dispersion forces are responsible for the cohesion and physical characteristics of these materials. By understanding the relationship between polarizability and the strength of dispersion forces, one can predict and explain a wide range of properties exhibited by nonmetals. For example, the high boiling points and condensation behavior of nonpolar gases, the ability of nonpolar substances to form thin, cohesive films, and the viscosity and surface tension of nonmetals can all be attributed to the attractive dispersion forces between their constituent atoms and molecules. This knowledge can be applied to understand the behavior of nonmetals in various contexts, from the liquefaction and storage of gases to the design of surface coatings and lubricants. By leveraging the principles governing dispersion forces, chemists and materials scientists can gain valuable insights into the structure-property relationships of nonmetals and utilize this information to develop novel applications and technologies.

Related terms

Intermolecular Forces:

Intermolecular forces are the attractive or repulsive forces between molecules, which determine the physical properties of a substance, such as boiling point, melting point, and surface tension.

Dipole Moments: A dipole moment is a measure of the separation of positive and negative electrical charges within a molecule, and it is a key factor in determining the strength of intermolecular forces, including dispersion forces.

Polarizability: Polarizability is the ability of a molecule or atom to have its electron cloud distorted by an external electric field, which is a crucial factor in the strength of dispersion forces.