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 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.

• The Shape of Molecules

  • One way in which the shapes of molecules manifest themselves experimentally is through molecular dipole moments.
  • A molecule which has one or more polar covalent bonds may have a dipole moment as a result of the accumulated bond dipoles.
  • Since there are two O-H bonds in water, their bond dipoles will interact and may result in a molecular dipole which can be measured.
  • The bond dipoles are colored magenta and the resulting molecular dipole is colored blue.
  • In the linear configuration (bond angle 180º) the bond dipoles cancel, and the molecular dipole is zero.

• 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+.

• Bond Polarity

  • In chemistry, bond polarity is the separation of electric charge along a bond, leading to a molecule or its chemical groups having an electric dipole or dipole moment.
  • The unequal sharing of electrons within a bond leads to the formation of an electric dipole (a separation of positive and negative electric charge).

• Hydrogen Bonding

  • The exceptionally strong dipole-dipole attractions that cause this behavior are called the hydrogen bond.
  • Hydrogen forms polar covalent bonds to more electronegative atoms such as oxygen, and because a hydrogen atom is quite small, the positive end of the bond dipole (the hydrogen) can approach neighboring nucleophilic or basic sites more closely than can other polar bonds.
  • Coulombic forces are inversely proportional to the sixth power of the distance between dipoles, making these interactions relatively strong, although they are still weak (ca. 4 to 5 kcal per mole) compared with most covalent bonds.