Permanent and Temporary Dipoles

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Permanent and Temporary Dipoles

Dipoles:

  • A molecule with a positive end and a negative end
  • When a molecule has a dipole it is called polarised
  • There are several ways a molecule can become polarised

Permanent Dipoles:

  • Permanent dipoles occur when a molecule has two atoms bonded together which have substantially different electro negatively, so that one atom attracts the shared electrons  much more than the other
  • Hydrogen chloride has a permanent dipole, because chlorine is much more electronegative than hydrogen, and so attracts the shared electrons more
  • Molecules with a permanent dipole are called polar molecules

Instantaneous Dipoles:

  • Some molecules do not possess a permanent dipole, because the atoms that are bonded together have the same, or very similar, electro negatively, so that the electrons are evenly shared
  • Even though the molecule doesn’t have a permanent dipole, a temporary, or instantaneous dipole can arise
  • Left on its own, this dipole only lasts for an instant before the swirling electron cloud changes its position, cancelling pout or even reversing the dipole
  • However, if there are other molecules nearby, the instantaneous dipole may affect them and produce induced dipoles
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Induces Dipoles:

  • If an unpolarised molecule finds itself next to a dipole, the unpolarised molecule may get a dipole induced in it
  • The dipole attracts or repels electrons in the charge cloud of the unpolarised molecule, inducing a dipole in it
  • A dipole can also be induced by the effect of an instantaneous dipole – this makes it possible for a whole series of dipoles to be set up in a substance that contains no permanent dipoles

Dipoles and Intermolecular Forces:

  • If a molecular substance contains dipoles, they can attract each other
  • All intermolecular forces ...

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