van der Waals interactions

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.