Chemical Bonding - Result Question 3
####3. The intermolecular interaction that is dependent on the inverse cube of distance between the molecules is (2015 Main)
(a) ion-ion interaction
(b) ion-dipole interaction
(c) London force
(d) hydrogen bond
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Answer:
Correct Answer: 3. (b)
Solution:
- Ion-ion interaction is dependent on the square of distance, i.e. ion-ion interaction $\propto \frac{1}{r^{2}}$
Similarly, ion-dipole interaction $\propto \frac{1}{r^{3}}$
London force $\propto \frac{1}{r^{6}}$ and dipole-dipole interaction $\propto \frac{1}{r^{3}}$
Superficially it seems as both ion-dipole interaction and hydrogen bonding vary with the inverse cube of distance between the molecules but when we look at the exact expressions of field (force) created in two situations, it comes as
$$ |E| \text { or }|F|=\frac{2|P|}{4 \pi \in r^{3}} $$
(In case of ion-dipole interaction) and $F=\frac{2 q^{2} r-4 q^{2} a}{4 \pi \in _0 r^{3}}$
(In case of dipole-dipole interaction)
From the above, it is clear that the ion-dipole interaction is the better answer as compared to dipole-dipole interaction, i.e. hydrogen bonding.
