ion-dipole forces

Examples of ion-dipole forces in the following topics:

• Ion-Dipole Force

  • The ion-dipole force is an intermolecular attraction between an ion and a polar molecule.
  • 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.
  • Ion-dipole forces are generated between polar water molecules and a sodium ion.

• 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.

• 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.

• 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).

• Dipole Moments

  • The electric dipole moment is a measure of polarity in a system.
  • There are many different types of dipole moments, including electric dipole moments, magnetic dipole moments, and topological dipole moments.
  • Among the subset of electric dipole moments are transition dipole moments, molecular dipole moments , bond dipole moments, and electron electric dipole moments.
  • It is essentially interchangeable with the "radius" variable in many other equations (such as those determining gravitational and electrostatic forces), except that it includes the factor of direction.
  • All dipoles will experience a torsional force, or torque, when they are placed in external electric fields.

• Bond Polarity

  • A polar molecule acts as an electric dipole which can interact with electric fields that are created artificially, or that arise from interactions with nearby ions or other polar molecules.
  • The Debye unit, D, is commonly used to express dipole moments.
  • In molecules containing more than one polar bond, the molecular dipole moment is just the vector addition of the individual bond dipole moments.
  • The bond dipoles add up to create a molecular dipole (indicated by the green arrow).
  • The net, molecular dipole moment of CO2 is therefore zero, and the molecule is nonpolar.

• 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–.

• Introduction to Bonding

  • They are related to weaker intermolecular forces, such as dipole-dipole interactions, the London dispersion forces, and hydrogen bonding.
  • The weaker forces will be discussed in a later concept.
  • Chemical bonds are the forces of attraction that tie atoms together.
  • Once the electrons have been transferred to the non-metal, both the metal and the non-metal are considered to be ions.
  • The two oppositely charged ions attract each other to form an ionic compound.