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Polarity of Bonds

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Polarity of Bonds - Lesson Summary

A covalent molecule with two oppositely charged poles is called a dipole. In such covalent bond there exists partial charge separation between the atoms of the molecule so it is called as polar covalent bond and the molecule is called as polar covalent molecule.

Charge separation between the atoms of the molecule creates polarity in these molecules.

There should be electronegativity difference between the atoms in polar covalent molecule.

Higher the electronegativity difference between the atoms of the molecule, higher will be the charge separation between the atoms of the molecule.

The crossed arrow above a Lewis structure indicates the direction of electron shift.

Dipole moment is defined as: "The product of the magnitude of the charge and the distance between the centers of the positive and negative charges."

μ = Q × r

Q = Charge in coulombs
r = Distance in meters

Dipole moment is a vector quantity, because it has both magnitude and direction.

The tendency of an anion to get polarized by a cation is called "polarisability".

If the extent of polarization is small, then the bond is more ionic in nature, but if the extent of polarization is more, then the bond is more covalent in nature.

These will be certain amount of ionic character present in polar covalent bond because of electronegativity difference.


Applications of dipole moment:

(i) Ionic character can be calculated using the value of dipole moment.

% of ionic character =

=100* (Experimental value of dipole moment/Theoretical value of 100% ionized molecule)

(ii) Geometry of the molecule can be predicted using the dipole moment.

(iii) Dipole moment is helpful in predicting nature of the molecule. Weather it is polar or non-polar in nature.

Ex:

(a) In BeCl₂ (linear molecule), the dipole moment gets zero, because of equal distribution of net charge on both sides which is neutralized to zero. So, it is non-polar molecule.

Similarly in Carbon dioxide molecule also the dipole moment gets neutralized to zero.

(b) In water molecule the dipole moment shifts towards oxygen (because of more electronegativity).

Therefore water is a polar molecule.

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