Question

Calculate the percentage ionic character of the HCl molecule. The bond length is 1.275$A{}^{\circ }$ and the observed dipole moment is 1.03 D.

Answer 1

Hint: For calculation of ionic character in a molecule, we need to determine the dipole moment within the molecule. The dipole moment is the physical property which is a measure of the polarity of a chemical bond between two atoms in a molecule. The higher the electronegativity difference between the two atoms, the more will be the ionic character to the bond and vice versa.

Complete answer:
- The dipole moment is the mathematical product of the total amount of positive charge or negative charge and the distance between the center of the charge distribution.
-For calculating the percent ionic character in a molecule, we need to follow the steps below-
(a) We start by calculating the dipole moment by taking the product of the magnitude of charge and separation between charges, i.e
     $$\mu =q\times r$$
where $\mu$ is the dipole moment
             q is the separated charge
             r is the distance between them
     Here, q= $1.6\times {10}^{-19}C$ ; r= $$1.275A{}^{\circ }\times {10}^{-10}m$$
So, dipole moment ($\mu$ ) $=1.6\times {10}^{-19}\times 1.275\times {10}^{-10}m$
                                            $=2.04\times {10}^{-29}cm$
(b) Now, we have to convert the centimeter into the standard unit of dipole moment, i.e Debye.
We know that, $1D=3.335\times {10}^{-30}cm$
                                 $$={\displaystyle \frac{2.04\times {10}^{-29}}{(3.335}}$$ $$={\displaystyle \frac{2.04\times {10}^{-29}}{\begin{array}{rl}& 3.335\times {10}^{-30}\\ & ={\displaystyle \frac{20.4}{3.335}}\\ & =6.1169D\end{array}}}$$
(c) Now, percentage ionic character $$={\displaystyle \frac{\exp value}{theoreticalvalue}}\times 100$$
                                                                 $$={\displaystyle \frac{1.03D}{6.1169D}}\times 100$$
                                                                  $=16.83$

Note: For calculating the dipole moment you need to remember the charge of an electron i.e,$1.6\times {10}^{-19}$ . For the calculation of percentage ionic character, remember the conversion units i.e,$1D=3.335\times {10}^{-30}cm$ .