Chemistry: Chemical Bonding: Dipole Moment: Carbon Dioxide and Water (For CBSE, ICSE, IAS, NET, NRA 2022)

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Dipole Moment

  • The charge separation in covalent bond results in the formation of an electrical dipole.
  • Each electrical dipole is characterized by dipole moment
  • Dipole moment (µ) = Magnitude of charge (Q) x Distance of separation (r)
  • It is measured by unit Debye which is represented by symbol D.
  • The SI unit of dipole moment is coulomb meter (Cm) .
  • The 2 units are related as .
  • The dipole moment depends upon the difference in electro negatives of 2 bonded atoms.
  • The dipole moment is vector quantity because it has both direction and magnitude.
  • The symbol is used to represent the dipole moment
  • The tail in the symbol points to the positive center and head pointing towards negative center.
  • By adding and subtracting dipole moment vectors, dipole moment of a molecule can be calculated. Some examples are shown below:

Carbon Dioxide

  • It is a linear triatomic molecule.
  • The C = O bond is polar and oxygen atom which have negative end of the bond dipole.
  • The dipole moments of C = O bonds have the same magnitude but in opposite directions, so they cancel each other, so, the net dipole moment of CO2 is zero.
Carbon Dioxide

Water

Diplole Moment: Water
  • Water is a non-linear and it has 2 atomic molecules.
  • Each H – O bond is a polar covalent bond and has a dipole moment.
  • The dipole moments of both the bonds are equal in magnitude, but due to non-linear shape, they do not cancel each other.
  • The net dipole moment of H2O molecule is 1.85 D (or 6.17 × 10 – 30 cm)

Boron Trifluoride, BF3

The net dipole moment of BF3 is zero due to its symmetrical planar structure.

Boron Trifluoride

Ammonia, NH3

  • NH3 has a pyramidal structure
  • It has three N – H bonds which are unsymmetrical in nature.
  • In each N – H bond, nitrogen is the negative center and hydrogen is the positive center.
  • It has an orbital dipole moment in which the electron pair is at the negative center.
  • The net dipole moment of NH3 is 1.47 D (4.90 × 10 – 30 Cm) .
Dipole Moment: Ammonia

Carbon Tetrachloride, CCl4

It has a net zero dipole moment due to its symmetrical tetrahedral shape.

Carbon Tetrachloride

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