London Dispersion Forces

Definition

London dispersion forces are a type of intermolecular force that arises from the temporary, spontaneous polarization of atoms or molecules. These forces are the weakest of the intermolecular forces, but they play a crucial role in the properties and behavior of many substances, including liquids, gases, and the noble gases.

5 Must Know Facts For Your Next Test

1. London dispersion forces arise from the temporary, spontaneous polarization of atoms or molecules due to the uneven distribution of electrons.
2. These forces are the weakest of the intermolecular forces, but they are responsible for the liquefaction of gases and the condensation of vapors.
3. London dispersion forces play a crucial role in the properties and behavior of many substances, including the noble gases, which have no permanent dipole moments.
4. The strength of London dispersion forces is directly proportional to the size and polarizability of the atoms or molecules involved.
5. London dispersion forces contribute to the surface tension and viscosity of liquids, as well as the solubility of non-polar substances in non-polar solvents.

Review Questions

• Explain how London dispersion forces arise and their relationship to the properties of substances.
  • London dispersion forces arise from the temporary, spontaneous polarization of atoms or molecules due to the uneven distribution of electrons. This temporary polarization creates a slight separation of charge, which leads to attractive forces between neighboring atoms or molecules. The strength of these forces is directly proportional to the size and polarizability of the particles involved. London dispersion forces are the weakest of the intermolecular forces, but they play a crucial role in the properties and behavior of many substances, including the liquefaction of gases, the condensation of vapors, and the solubility of non-polar substances in non-polar solvents.
• Describe the role of London dispersion forces in the properties of liquids and the noble gases.
  • London dispersion forces contribute to the physical properties of liquids, such as surface tension and viscosity. The strength of these forces determines the cohesion between molecules, which affects the ease with which the molecules can move past one another. Additionally, London dispersion forces are responsible for the liquefaction of gases and the condensation of vapors, as they hold the molecules together in the liquid state. In the case of the noble gases, which have no permanent dipole moments, London dispersion forces are the primary intermolecular force that determines their physical properties, such as their relatively low boiling points compared to other elements.
• Analyze the relationship between the size and polarizability of atoms or molecules and the strength of London dispersion forces.
  • The strength of London dispersion forces is directly proportional to the size and polarizability of the atoms or molecules involved. Larger atoms or molecules have a greater number of electrons, which increases the likelihood of temporary, spontaneous polarization. This, in turn, leads to stronger attractive forces between neighboring particles. Similarly, more polarizable atoms or molecules, which can more easily develop a temporary dipole moment, will experience stronger London dispersion forces. The relationship between size, polarizability, and the strength of London dispersion forces is crucial in understanding the physical properties and behavior of a wide range of substances, from liquids and gases to the noble gases.

Related terms

Intermolecular Forces:

Intermolecular forces are the attractive or repulsive forces that exist between molecules, which determine the physical properties of a substance.

Polarization:

Polarization is the process by which an atom or molecule develops a slight separation of charge, resulting in a temporary or permanent dipole moment.

van der Waals Forces:

van der Waals forces are a group of intermolecular forces that include London dispersion forces, dipole-dipole interactions, and dipole-induced dipole interactions.