van der Waals interactions

(noun)

A weak force of attraction between electrically neutral molecules that collide with or pass very close to each other. The van der Waals force is caused by temporary attractions between electron-rich regions of one molecule and electron-poor regions of another.

Related Terms

  • lectronegativity
  • Electronegativi
  • hydrogen bond
  • electronegativity
  • Electronegativity
  • Hydrogen bonds

Examples of van der Waals interactions in the following topics:

  • 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.
  • Covalent Bonds and Other Bonds and Interactions

    • Two types of weak bonds that frequently occur are hydrogen bonds and van der Waals interactions.
    • The weak interaction between the δ+ charge of a hydrogen atom from one molecule and the δ- charge of a more electronegative atom is called a hydrogen bond.
    • 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.
    • In this interactive, you can explore how different types of molecules interact with each other based on their bonds.
  • 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.
    • Also, as one moves down a column in the periodic table, the outer electrons are more loosely bound to the nucleus, increasing the polarisability of the atom, and thus its propensity to van der Waals-type interactions.
    • 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

    • 020), we must also concern ourselves with interactions between molecules, as well as with their individual structures.
    • Indeed, many of the physical characteristics of compounds that are used to identify them (e.g. boiling points, melting points and solubilities) are due to intermolecular interactions.
    • All atoms and molecules have a weak attraction for one another, known as van der Waals attraction.
    • 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.
  • The Effect of Intermolecular Forces

    • The Ideal Gas Law does not account for these interactions.
    • 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.
  • 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.
    • 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?
  • The Effect of the Finite Volume

    • Ideal gases are assumed to be composed of point masses whose interactions are restricted to perfectly elastic collisions; in other words, a gas particles' volume is considered negligible compared to the container's total volume.
    • The van der Waals equation modifies the ideal gas law to correct for this excluded volume, and is written as follows:
    • Ideal gases are assumed to be composed of point masses that interact via elastic collisions.
    • Demonstrate an understanding of the van der Waals equation for non-ideal gases.
  • Real Gases

    • The Ideal Gas Law assumes that a gas is composed of randomly moving, non-interacting point particles.
    • 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.
  • Reaction Rates and Kinetics

    • When they are crowded together, van der Waals repulsions produce an unfavorable steric hindrance.
    • In many reactions atomic or molecular orbitals interact in a manner that has an optimal configurational or geometrical alignment.
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