Polar Covalent bond
and Partial ionic Character/Factors affecting The Strength of Ionic
Character
Since two atoms of
different elements do not have exactly the same attraction for electrons in a bond, all bonds between unlike atoms are polar to some extent. Polar
covalent bond is not a pure covalent
bond but it has partial ionic character.
The amount of ionic character in polar bond indicates the extent of shifting the electron pair (i.e. extent of charge separation).
Ionic character of covalent bond mainly depends upon electronegativity difference between the two bonded atoms. . Greater is the electronegativity difference between the bonded atoms, greater will be the magnitude of ionic character in the covalent bond. The difference in the electronegativity of the two bonded atoms primarily determines the extent of the ionic character of a covalent bond. However size of the atom and bond length also influence the bond strength.
The
electronegativities of some common elements in their relative order are given
below:
H (2.1) <
I (2.4) < C & S (2.5) < Br (2.8) < Cl & N (3.0) < O (3.5)
< F (4.0)
HF is 43%
ionic while HCl is 17% ionic.
When the difference of EN of the two atoms is almost same then relative size of atoms decide the strength of ionic character.
A graph showing the % age ionic character and difference in electronegativity between the two atoms is shown below:
Calculation of
Percentage Ionic Character
several empirical equations have been proposed to calculate the percentage
ionic character in the bond. It is important to note that no bond (even ionic)
in chemistry is 100% ionic. The following methods have been proposed for this
purpose:
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