Polar bond

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In chemistry, a polar bond is a type of bond between two atoms in which electrons are shared unequally. Because of this, one end of the bond has a fractional negative charge and the other a positive charge.

  • Non-polar bonds occur when the difference in electronegativity between the two atoms is less than 0.4
  • Polar bonds occur when the difference in electronegativity between the two atoms is between 0.4 and 2.0
  • Ionic bonds occur when the difference in electronegativity between the two atoms is greater than 2.0
Water has two polar O-H bonds in a bent geometry

If the bond dipole moments of the molecule do not cancel, the molecule is polar. For example, the water molecule (H2O) contains two polar O-H bonds in a bent (nonlinear) geometry. The bond dipole moments which do not cancel, so that the molecule forms a molecular dipole with its negative pole at the oxygen and its positive pole midway between the two hydrogen atoms. In the figure each bond joins the central O atom with a negative charge (red) to an H atom with a positive charge (blue).

Carbon dioxide has two polar C-O bonds in a linear geometry

However not every molecule with polar bonds is a polar molecule. Carbon dioxide (CO2) has two polar C-O bonds, but the geometry of CO2 is linear so that the two bond dipole moments cancel and there is no net molecular dipole moment; the molecule is non-polar.

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