Van der Waals forces

(noun)

The sum of the attractive or repulsive forces between molecules (or between parts of the same molecule) other than those due to covalent bonds, or the electrostatic interaction of ions with one another, with neutral molecules, or with charged molecules.

Related Terms

  • dipole
  • dispersion forces
  • nonpolar
  • polar
  • London dispersion forces

Examples of Van der Waals forces in the following topics:

  • Dispersion Force

    • London dispersion forces are part of the van der Waals forces, or weak intermolecular attractions.
    • Van der Waals forces help explain how nitrogen can be liquefied.
    • London dispersion forces allow otherwise non-polar molecules to have attractive forces.
    • There are two kinds of attractive forces shown in this model: Coulomb forces (the attraction between ions) and Van der Waals forces (an additional attractive force between all atoms).
    • How does changing the Van der Waals attraction or charging the atoms affect the melting and boiling point of the substance?
  • Introduction to Intermolecular Forces

    • All atoms and molecules have a weak attraction for one another, known as van der Waals attraction.
    • This attractive force has its origin in the electrostatic attraction of the electrons of one molecule or atom for the nuclei of another.
    • If there were no van der Waals forces, all matter would exist in a gaseous state, and life as we know it would not be possible.
    • It should be noted that there are also smaller repulsive forces between molecules that increase rapidly at very small intermolecular distances.
  • Hydrogen Bonding and Van der Waals Forces

    • Hydrogen bonds and van der Waals interactions are two types of weak bonds that are necessary to the basic building blocks of life.
    • Two weak bonds that occur frequently are hydrogen bonds and van der Waals interactions.
    • Like hydrogen bonds, van der Waals interactions are weak attractions or interactions between molecules.
    • Van der Waals attractions can occur between any two or more molecules and are dependent on slight fluctuations of the electron densities, which are not always symmetrical around an atom.
    • Explore how Van der Waals attractions and temperature affect intermolecular interactions.
  • Molecular Crystals

    • Molecules held together by van der Waals forces form molecular solids.
    • Liquids and solids composed of molecules are held together by van der Waals (or intermolecular) forces, and many of their properties reflect this weak binding.
    • Because dispersion forces and the other van der Waals forces increase with the number of atoms, large molecules are generally less volatile, and have higher melting points than smaller ones.
    • There are two kinds of attractive forces shown in this model: Coulomb forces (the attraction between ions) and Van der Waals forces (an additional attractive force between all atoms).
    • How does changing the Van der Waals attraction or charging the atoms affect the melting and boiling point of the substance?
  • Friction: Static

    • When surface area is below the micrometer range, Van der Waals' forces, electrostatic interactions and hydrogen bonding can cause two materials to adhere to one another.
    • Like kinetic friction, the force of static friction is given by a coefficient multiplied by the normal force.
    • As with all frictional forces, the force of friction can never exceed the force applied.
    • Thus the force of static friction will vary between 0 and $_sF_n$ depending on the strength of the applied force.
    • Any force larger than that overcomes the force of static friction and causes sliding to occur.
  • The Effect of Intermolecular Forces

    • Intermolecular forces describe the attraction and repulsion between particles.
    • To correct for intermolecular forces between gas particles, J.D. van der Waals introduced a new term into the Ideal Gas Equation in 1873.
    • By adding the term n2a/V2 to pressure, van der Waals corrected for the slight reduction in pressure due to the interaction between gas particles:
    • In the term above, a is a constant specific to each gas and V is the volume. van der Waals also corrected the volume term by subtracting out the excluded volume of the gas.
    • The full van der Waals equation of state is written as:
  • Van der Waals Equation

    • Derived by Johannes Diderik van der Waals in 1873, the van der Waals equation modifies the Ideal Gas Law; it predicts the properties of real gases by describing particles of non-zero volume governed by pairwise attractive forces.
    • Isotherm (plots of pressure versus volume at constant temperature) can be produced using the van der Waals model.
    • Notice that the van der Waals equation becomes the Ideal Gas Law as these two correction terms approach zero.
    • The van der Waals model offers a reasonable approximation for real gases at moderately high pressures.
    • Distinguish the van der Waals equation from the Ideal Gas Law.
  • The Effect of the Finite Volume

    • At low temperatures where the contribution of intermolecular forces becomes significant
    • The van der Waals equation modifies the ideal gas law to correct for this excluded volume, and is written as follows:
    • Demonstrate an understanding of the van der Waals equation for non-ideal gases.
  • Real Gases

    • The model also fails for most heavy gases (including many refrigerants) and for gases with strong intermolecular forces (such as water vapor).
    • a is an empirically determined factor that corrects for the intermolecular forces between gas particles; it is specific for each gas
    • It is almost always more accurate than the van der Waals equation and frequently more accurate than some equations with more than two parameters.
    • Note that a and b here are defined differently than in the van der Waals equation.
    • However, these systems are used less frequently than are the van der Waals and Redlich-Kwong models.
  • Covalent Bonds and Other Bonds and Interactions

    • Two types of weak bonds that frequently occur are hydrogen bonds and van der Waals interactions.
    • Individual hydrogen bonds are weak and easily broken; however, they occur in very large numbers in water and in organic polymers, and the additive force can be very strong.
    • Like hydrogen bonds, van der Waals interactions are weak interactions between molecules.
    • Van der Waals attractions can occur between any two or more molecules and are dependent on slight fluctuations of the electron densities, which can lead to slight temporary dipoles around a molecule.
Subjects
  • Accounting
  • Algebra
  • Art History
  • Biology
  • Business
  • Calculus
  • Chemistry
  • Communications
  • Economics
  • Finance
  • Management
  • Marketing
  • Microbiology
  • Physics
  • Physiology
  • Political Science
  • Psychology
  • Sociology
  • Statistics
  • U.S. History
  • World History
  • Writing

Except where noted, content and user contributions on this site are licensed under CC BY-SA 4.0 with attribution required.