ion-induced dipole force

Examples of ion-induced dipole force in the following topics:

• Ion-Dipole Force

  • Ion-dipole and ion-induced dipole forces operate much like dipole-dipole and induced dipole-dipole interactions.
  • However, ion-dipole forces involve ions instead of solely polar molecules.
  • Ion-dipole forces are stronger than dipole interactions because the charge of any ion is much greater than the charge of a dipole; the strength of the ion-dipole force is proportionate to ion charge.
  • An ion-induced dipole force occurs when an ion interacts with a non-polar molecule.
  • Like a dipole-induced dipole force, the charge of the ion causes a distortion of the electron cloud in the non-polar molecule, causing a temporary partial charge.

• Dipole-Dipole Force

  • Intermolecular forces are the forces of attraction or repulsion which act between neighboring particles (atoms, molecules, or ions).
  • Ion-dipole forces: electrostatic interaction involving a partially charged dipole of one molecule and a fully charged ion.
  • Instantaneous dipole-induced dipole forces or London dispersion forces: forces caused by correlated movements of the electrons in interacting molecules, which are the weakest of intermolecular forces and are categorized as van der Waals forces.
  • Dipoles may form associations with other dipoles, induced dipoles or ions.
  • An important type of dipole-dipole forces are hydrogen bonds.

• The Effect of Intermolecular Forces

  • At high pressures and low temperatures, intermolecular forces between gas particles can cause significant deviation from ideal behavior.
  • Intermolecular forces describe the attraction and repulsion between particles.
  • When the weight of individual gas molecules becomes significant, London dispersion forces, or instantaneous dipole forces, tend to increase, because as molecular weight increases, the number of electrons within each gas molecule tends to increase as well.
  • The dipoles can then induce further dipoles in neighboring molecules, and the unlike charges between molecules can attract one another.
  • At high pressures and low temperatures, these attractive forces can become significant.

• Dispersion Force

  • These intermolecular forces are also sometimes called "induced dipole-induced dipole" or "momentary dipole" forces.
  • London dispersion forces are part of the van der Waals forces, or weak intermolecular attractions.
  • If there are no dipoles, what would make the nitrogen atoms stick together to form a liquid?
  • 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).

• Polarization

  • Different materials will react differently to an induced field, depending on their dielectric constant.
  • This separation creates a dipole moment, as shown in .
  • On the molecular level, polarization can occur with both dipoles and ions.
  • Ions are still free from one another and will naturally move at random.
  • The atom's dipole moment is represented by M.

• Intermolecular Forces and Solutions

  • Many intermolecular forces can contribute to solvation, including hydrogen bonding, dipole-dipole forces, and Van Der Waals forces.
  • Another common example of these forces at work is an ion-dipole interaction, which arises when water solvates ions in solution.
  • The positive ion, Na+, is surrounded by water molecules that have the negative dipoles of the water, or the oxygen, pointing towards the cation.
  • In this case, the anion Cl- is solvated by the positive dipoles of water, which are represented by hyrogen atoms.
  • Notice the negative dipole or the oxygen molecules are 'facing' the Na+.

• Solutions and Heats of Hydration

  • Since the coulombic forces that bind ions and highly polar molecules into solids are quite strong, we might expect these solids to be insoluble in most solvents.
  • The electrically-charged ions undergo ion-dipole interactions with water to overcome strong coulombic attraction, and this produces an aqueous solution.
  • This dipole arises from the disparity in electronegativity present in the O-H bonds within the water molecule.
  • As a consequence, ions in aqueous solutions are always hydrated; that is, they are quite tightly bound to water molecules through ion-dipole interactions.
  • The relative strengths of these two intermolecular forces is apparent: ion-dipole interactions are stronger than hydrogen bond interactions.

• Ferromagnetism

  • Ferromagnetism is the strongest type—it is the only type that creates forces strong enough to be felt, and is responsible for the common phenomena of magnetism encountered in everyday life.
  • This induced magnetization can be made permanent if the material is heated and then cooled, or simply tapped in the presence of other magnets, as shown in .
  • Ferromagnetism arises from the fundamental property of an electron; it also carries charge to have a dipole moment.
  • This dipole moment comes from the more fundamental property of the electron—its quantum mechanical spin.
  • Not only do ferromagnetic materials respond strongly to magnets (the way iron is attracted to magnets), they can also be magnetized themselves—that is, they can be induced to be magnetic or made into permanent magnets.

• Paramagnetism and Diamagnetism

  • The magnetic moment induced by the applied field is linear in the field strength; it is also rather weak.
  • Constituent atoms or molecules of paramagnetic materials have permanent magnetic moments (dipoles), even in the absence of an applied field.
  • Even in the presence of the field there is only a small induced magnetization because only a small fraction of the spins will be oriented by the field.
  • For example, the Lorentz force on electrons causes them to circulate around forming eddy currents.
  • The eddy currents then produce an induced magnetic field opposite the applied field, resisting the conductor's motion.

• Solvent Effects

  • The first is the ability of solvent molecules to orient themselves between ions so as to attenuate the electrostatic force one ion exerts on the other.
  • High dielectric constant solvents such as water (ε=80), dimethyl sulfoxide (ε=48) & N,N-dimethylformamide (ε=39), usually have polar functional groups, and often high dipole moments.
  • The water dipoles are drawn as red arrows, and partial charges are noted.
  • Additional water molecules are oriented in secondary and tertiary layers about the ions.
  • Because of their greater charge density, small ions and highly charged ions, such as F– and Ca2+, require greater solvation than large or singly charged ions, such as Na+ or Cl–.