PERCENTAGE OF IONIC CHARACTER

Every ionic compound having some percentage of covalent character according to Fajan’s rule. The percentage of ionic character in a compound having some covalent character can be calculated by the following equation.

The percent ionic character = Observed dipole moment/Calculated dipole moment assuming 100% ionic bond × 100

Example: Dipole moment of KCl is 3.336 × 10–29 coulomb metre which indicates that it is highly polar molecule. The interatomic distance between k+ and Cl is 2.6 ×10–10 m. Calculate the dipole moment of KCl molecule if there were opposite charges of one fundamental unit located at each nucleus. Calculate the percentage ionic character of KCl.

Solution: Dipole moment μ = e × d coulomb metre

             For KCl d = 2.6 × 10–10 m

             For complete separation of unit charge

             e = 1.602 × 10–19 C

             Hence μ = 1.602 × 10–19 × 2.6 × 10–10 = 4.1652 × 10–29 Cm

             μKCl = 3.336 × 10–29 Cm

             ∴ % ionic character of KCl = 3.336×10–29/4.165×10–29  = 80.09%

Example. Calculate the % of ionic character of a bond having length = 0.83 Å and 1.82 D as it’s observed dipole moment.

Solution: Tocalculate μ considering 100% ionic bond

              = 4.8 × 10–10 × 0.83 × 10–8esu cm

              = 4.8 × 0.83 × 10–18 esu cm = 3.984 D

              ∴ % ionic character = 1.82/3.984 × 100 = 45.68

The example given above is of a very familiar compound called HF. The % ionic character is nearly 43.25%, so the % covalent character is (100 – 43.25) = 56.75%. But from the octet rule HF should have been a purely covalent compound but actually it has some amount of ionic character in it, which is due to the electronegativity difference of H and F. Similarly knowing the bond length and observed dipole moment of HCl, the % ionic character can be known. It was found that HCl has 17% ionic character. Thus it can be clearly seen that although we call HCl and HF as covalent compounds but it has got appreciable amount of ionic character. So from now onwards we should call a compound having more of ionic less of covalent and vice versa rather than fully ionic or covalent.

Related Resources
Hydrogen Bonding

HYDROGEN BONDING Introduction: An atom of hydrogen...

Dipole Moment

DIPOLE MOMENT Difference in polarities of bonds is...

Application of Molecular to Homonuclear Diatomic Molecules

Application of MOT to homonuclear diatomic...

Solutions to Miscellaneous Exercises

ANSWER TO MISCELLANEOUS EXERCISES Exercise 1: The...

Rule for Determination of Total Number of Hybrid Orbitals

Rule for determination of total number of hybrid...

Formation of Ionic Bond

Energy Change During the Formation of Ionic Bond...

Valence Shell Electron Pair Repulsion Theory

VALENCE SHELL ELECTRON PAIR REPULSION (VSEPR)...

Determination of Lattice Energy

Determination of Lattice Energy The direct...

Solved Examples based on Hybridization

Solved Examples Based on Hybridization Example 8:...

Effect of Hydrogen Bonding

Effect of Hydrogen Bonding Hydrogen bonding has...

Co-ordinate Covalency

CO-ORDINATE COVALENCY A covalent bond results from...

Molecular Orbitals of Some Diatomic Heteronuclei Molecules

M.O. of Some Diatomic Heteronuclei Molecules The...

Examples Based on Bond Angle

Solved Examples Example: Why the bond angle of H...

Miscellaneous Exercises of Chemical Bonding

MISCELLANEOUS EXERCISES Exercise 1: Compare the...

Hybridization

HYBRIDIZATION The tetravalency shown by carbon is...

Maximum Covalency

Maximum Covalency Elements which have vacant...

Molecular Orbital Theory

MOLECULAR ORBITAL THEORY In Molecular Orbital...

Factors Governing Polarization and Polarisability

FACTORS GOVERNING POLARIZATION AND POLARISABILITY...

Origin of Intermolecular Forces

Origin of Intermolecular Forces: Intermolecular...

Electrovalency

ELECTROVALENCY This type of valency involves...

Indroduction to Chemical Bonding

INTRODUCTION A molecule is formed if it is more...

Importance of Hydrogen Bonding in Biological Systems

Importance of Hydrogen Bonding in Biological...

Covalency

COVALENCY This type of valency involves sharing of...

Regular Geometry and Irregular Geometry

Regular Geometry Molecules in which the central...

Examples of Hybridization

Examples of Hybridization We have already...

Bond Characteristics

BOND CHARACTERISTICS 1. Bond Length: The distance...

Characteristics of Ionic Compounds

Characteristics of ionic compounds : The following...

Calculation of Bond Moments

Calculation of Resultant Bond Moments Let AB and...

Solved Problems of Chemical Bonding

SOLVED PROBLEMS Board Type Questions Prob 2....

Resonance

RESONANCE There may be many molecules and ions for...

Rules for Writing Resonating Structures

Rules for Writing Resonating Structures Only...