Question

The percent ionic character in HCl is 18.08. the observed dipole moment is 1.08 D. Find the internuclear distance in HCl?

Answer 1

Hint: Molecules like H-X having two polar ends are known as dipoles are polar molecules. The measure of polarity in a polar compound is given by its dipole moment.


Step by step answer: Dipole moment is defined as the product of the net positive or negative charge and distance between the two charged ends, i.e. the dipole length.
Dipole moment$\mu = e \times d$(where e is electric charge and d is the distance between the charges)
It is measured in debye unit(D). Let us now understand the concept of percentage ionic character, every ionic compound has 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)$ \times 100$
In the given compound of HCl we have been asked to find “d” internuclear distance in HCl. Therefore we will put the given values in the equation above which will be
Let the calculated dipole moment be x
$
  18.08 = \dfrac{{1.08}}{x} \times 100 \\
 \Rightarrow x = \dfrac{{108}}{{18.08}} = \dfrac{{10800}}{{1808}} = 5.97D \\
 $
We know that 1D=3.336$ \times {10^{ - 30}}coloumb - metre$
so,
5.97D=5.97*3.336$ \times {10^{ - 30}}coloumb - metre$=$19.9 \times {10^{ - 30}}C - m = 0.0199 \times {10^{ - 27}}C - cm$
x=$\mu $=$e \times d$
$d = \dfrac{\mu }{e} = \dfrac{{0.0199 \times {{10}^{ - 27}}}}{{1.602 \times {{10}^{ - 19}}}} = 0.0124 \times {10^{ - 19}}m$
Further dipole moment is a vector quantity and is depicted by a small arrow with tail on the positive centre and head pointing towards the negative centre.

Note: The existence of a hundred percent ionic or covalent bond represents an ideal situation. In reality no bond or compound is either completely covalent or ionic.In the case of polyatomic molecules the dipole moment not only depends upon the individual dipole moments of bond but on spatial arrangement as well.