Bond Polarity

Bond Polarity is used to describe the sharing of electrons between atoms in covalent bonding.  A polar covalent bond is a bond in which there is unequal sharing of electrons between atoms while a nonpolar covalent bond has equal sharing of electrons between atoms.

How can we distinguish between polar and nonpolar bond?

Electronegativity is a property of the elements used to determine if the sharing of electrons between atoms in covalent bonding is equal or not equal.  Electronegativity is defined as the ability of an atom in a molecule to attract electrons to itself.  The greater the electronegativity value the greater its ability to attracts electrons to itself.

The difference in electronegativity between atoms in a molecule is used to predict the sharing of electrons.  Consider the example below:

Example 1.

Compound   :         F₂

Electronegativity difference :     4.0 - 4.0  =  0

Type of Bond :    Nonpolar covalent bond



Example 2

Compound   :  HF

Electronegativity difference :  4.0 -  2.1 =  1.9

Type of Bond    :   Polar covalent bond



Example 3.

Compound   :    LiF

Electronegativity Difference:  4.0 - 1.0  = 3.0

Type of Bond  :    Ionic Bond



The three examples above show how the type of bond be identified.  In example 1,  the difference between the electronegativity of two F atoms is 0, which is an indication that the sharing of electrons between atoms are equal.  Therefore, a nonpolar covalent bond results when the electronegativity difference between atoms is from 0 to 0.4.  In this difference of electronegativity still shows that the sharing of electrons is equal between atoms.

In example 2, we can see that the difference of electronegativity values between atoms is 1.9, this shows that the sharing of electrons is not equal.  Therefore, a polar covalent bond results when the electronegativity difference between atoms ranges from 0.5 to 1.9.   At this difference the sharing of electrons between atoms resulted in unequal sharing.

In example 3, the difference of electronegativity values between atoms is 3.0 which means that there is a big difference of electronegativity which resulted the transfer of electrons between one atom to another atom.  Therefore, Ionic bond exist when the electronegativity difference is from 2.0 above.