dipole

Examples of dipole 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.
  • Ion-dipole bonding is also stronger than hydrogen bonding.
  • 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

  • Dipole-dipole interactions are intermolecular attractions that result from two permanent dipoles interacting.
  • Dipole-dipole forces: electrostatic interactions of permanent dipoles in molecules; includes hydrogen bonding.
  • Dipole-dipole interactions are electrostatic interactions between the permanent dipoles of different molecules.
  • Dipoles may form associations with other dipoles, induced dipoles or ions.
  • An important type of dipole-dipole forces are hydrogen bonds.

• 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.
  • This torque rotates the dipole to align it with the field.
  • Relate the electric dipole moment to the polarity in a system

• Dipole Moment

  • A dipole exists when a molecule has areas of asymmetrical positive and negative charge.
  • The bond dipole moment uses the idea of the electric dipole moment to measure a chemical bond's polarity within a molecule.
  • Debye was the first to extensively study molecular dipoles.
  • Molecules with only two atoms contain only one (single or multiple) bond, so the bond dipole moment is the molecular dipole moment.
  • To calculate the dipole for the entire molecule, add all the individual dipoles of the individual bonds as their vector.

• Bond Polarity

  • Dipoles are conventionally represented as arrows pointing in the direction of the negative end.
  • 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.

• Dispersion Force

  • Temporary dipoles are created when electrons, which are in constant movement around the nucleus, spontaneously come into close proximity.
  • This uneven distribution of electrons can make one side of the atom more negatively charged than the other, thus creating a temporary dipole, even on a non-polar molecule.
  • These intermolecular forces are also sometimes called "induced dipole-induced dipole" or "momentary dipole" forces.
  • Although charges are usually distributed evenly between atoms in non-polar molecules, spontaneous dipoles can still occur.
  • If there are no dipoles, what would make the nitrogen atoms stick together to form a liquid?

• The Effect of Intermolecular Forces

  • 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.
  • More electrons means that when two gas molecules collide or converge, the electron clouds around each nucleus can repel one another, thereby creating an "instantaneous dipole" (a separation of charge resulting in a partial positive and partial negative charge across the molecule).
  • The dipoles can then induce further dipoles in neighboring molecules, and the unlike charges between molecules can attract one another.

• A Physical Aside: Multipole Radiation

  • It is possible to calculate the radiation field to higher order in $L/(c\tau)$.This is necessary if the dipole moment vanishes, for example.
  • where $k\equiv\omega/c$$n=0$ gives the dipole radiation, $n=1$ gives the quadrupole radiation and so on.

• Selection Rules

  • We can determine the selection rules for dipole emission by examining the definition of the dipole matrix element
  • First let's calculate the dipole matrix element after a parity transformation that takes ${\bf r} \rightarrow -{\bf r}$.
  • The first condition holds because the dipole operator does not couple to the spin of the electrons and the final condition exists because a photon carries away one unit of angular momentum.
  • On the other hand transitions that don't follow these rules can proceed through magnetic dipole or higher order multipole interactions.

• Polarization

  • This separation creates a dipole moment, as shown in .
  • On the molecular level, polarization can occur with both dipoles and ions.
  • One example of a dipole molecule is water, (H2O), which has a bent shape (the H-O-H angle is 104.45°) and in which the oxygen pulls electron density away from the H atoms, leaving the H relatively positive and the O relatively negative, as shown in .
  • Water is an example of a dipole molecule, which has a bent shape (the H-O-H angle is 104.45°) and in which the oxygen pulls electron density away from the H atoms, leaving the H relatively positive and the O relatively negative.
  • The atom's dipole moment is represented by M.